Gene Summary

Gene:PPP2CA; protein phosphatase 2, catalytic subunit, alpha isozyme
Aliases: RP-C, PP2Ac, PP2CA, PP2Calpha
Summary:This gene encodes the phosphatase 2A catalytic subunit. Protein phosphatase 2A is one of the four major Ser/Thr phosphatases, and it is implicated in the negative control of cell growth and division. It consists of a common heteromeric core enzyme, which is composed of a catalytic subunit and a constant regulatory subunit, that associates with a variety of regulatory subunits. This gene encodes an alpha isoform of the catalytic subunit. [provided by RefSeq, Jul 2008]
Databases:OMIM, HGNC, GeneCard, Gene
Protein:serine/threonine-protein phosphatase 2A catalytic subunit alpha isoform
Source:NCBIAccessed: 25 June, 2015


What does this gene/protein do?
Show (42)
Pathways:What pathways are this gene/protein implicaed in?
Show (18)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 25 June 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Transfection
  • Cell Proliferation
  • Wilms Tumour
  • BAD
  • ral GTP-Binding Proteins
  • DNA Sequence Analysis
  • Sequence Deletion
  • Up-Regulation
  • Phosphoprotein Phosphatases
  • Base Sequence
  • Phosphorylation
  • Signal Transduction
  • Down-Regulation
  • Gene Expression Profiling
  • Breast Cancer
  • Succinate Dehydrogenase
  • Proteins
  • Neoplastic Cell Transformation
  • Protein Phosphatase 2
  • Western Blotting
  • Cancer Gene Expression Regulation
  • Cervical Cancer
  • siRNA
  • Tandem Repeat Sequences
  • Receptor, erbB-2
  • Molecular Sequence Data
  • Viral Proteins
  • p53 Protein
  • Proto-Oncogene Proteins
  • Spindle Apparatus
  • Chromosome 5
  • Mutation
  • Tumor Suppressor Proteins
  • Vitamin D3 24-Hydroxylase
  • Apoptosis
  • Proteolysis
  • RNA Interference
  • Lung Cancer
  • Skin Cancer
Tag cloud generated 25 June, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: PPP2CA (cancer-related)

Yu N, Kakunda M, Pham V, et al.
HSP105 recruits protein phosphatase 2A to dephosphorylate β-catenin.
Mol Cell Biol. 2015; 35(8):1390-400 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
The Wnt/β-catenin pathway causes accumulation of β-catenin in the cytoplasm and its subsequent translocation into the nucleus to initiate the transcription of the target genes. Without Wnt stimulation, β-catenin forms a complex with axin (axis inhibitor), adenomatous polyposis coli (APC), casein kinase 1α (CK1α), and glycogen synthase kinase 3β (GSK3β) and undergoes phosphorylation-dependent ubiquitination. Phosphatases, such as protein phosphatase 2A (PP2A), interestingly, also are components of this degradation complex; therefore, a balance must be reached between phosphorylation and dephosphorylation. How this balance is regulated is largely unknown. Here we show that a heat shock protein, HSP105, is a previously unidentified component of the β-catenin degradation complex. HSP105 is required for Wnt signaling, since depletion of HSP105 compromises β-catenin accumulation and target gene transcription upon Wnt stimulation. Mechanistically, HSP105 depletion disrupts the integration of PP2A into the β-catenin degradation complex, favoring the hyperphosphorylation and degradation of β-catenin. HSP105 is overexpressed in many types of tumors, correlating with increased nuclear β-catenin protein levels and Wnt target gene upregulation. Furthermore, overexpression of HSP105 is a prognostic biomarker that correlates with poor overall survival in breast cancer patients as well as melanoma patients participating in the BRIM2 clinical study.

Liu F, Ji F, Ji Y, et al.
Dissecting the mechanism of colorectal tumorigenesis based on RNA-sequencing data.
Exp Mol Pathol. 2015; 98(2):246-53 [PubMed] Related Publications
OBJECTIVE: This study aimed to identify the differentially expressed genes (DEGs), mutated genes and fusion genes in colorectal cancer.
MATERIALS AND METHODS: RNA-sequencing data (ID: SRP009386) from cancerous, paracancerous non-tumor and distant normal tissue from one Chinese patient with stage III colorectal cancer were downloaded from Sequence Read Archive. Quality control was checked using FastQC, followed by sequence alignment against the hg19 reference genome using TopHat v1.3.3. The expression levels were quantified using Cufflinks, followed by DEGs screening using NOISeq. Enrichment analysis was performed using DAVID. Transcription factors were screened using TRANSFA. Mutated loci were identified using SAMTools and VCFTools. Gene fusion events were detected by TopHat-fusion.
RESULTS: In total 2440, 1887 and 834 DEGs were respectively detected in cancerous vs. normal tissue, cancerous vs. paracancerous tissue and paracancerous vs. normal tissue. The up-regulated genes from cancerous and paracancerous tissue compared with normal tissue were enriched in "extracellular matrix receptor interaction" and "focal adhesion pathway" as well as some biological processes except for "negative regulation of programmed cell death" uniquely presenting in cancer. Dysregulated transcription factors including SOX4, BCL6, CEBPB and MSX2 were enriched in the unique biological process. Trp53 was identified with one mutated locus 7577142 (C → T) on chromosome 17. BCL6 also experienced missense mutation. Additionally, COL1A1-PPP2R2C and EXPH5-COL1A2 were observed fusion genes in cancer tissue.
CONCLUSIONS: The unique biological process in cancer tissue may be the cause for colorectal carcinogenesis. The screened transcription factors, mutated genes and fusion genes may contribute to the progression of colorectal cancer.

Wu Y, Gu TT, Zheng PS
CIP2A cooperates with H-Ras to promote epithelial-mesenchymal transition in cervical-cancer progression.
Cancer Lett. 2015; 356(2 Pt B):646-55 [PubMed] Related Publications
The oncoprotein Cancerous Inhibitor of PP2A (CIP2A) has been reported to interact with Protein phosphatase 2 (PP2A) to stabilize c-Myc and prevent its degradation, and high expression levels of CIP2A have been proved to be related to poor clinical outcomes in multiple cancers. Here, we not only proved that the expression of CIP2A is positively correlated with lymph-node metastasis and cervical-cancer progression, but also revealed a close correlation between the protein's expression and the expression levels of two core epithelial-to-mesenchymal transition (EMT) markers, Vimentin and Snail. In addition, we manipulated CIP2A expression to regulate EMT conversion and employed a pull-down assay, mass-spectrometric (MS) peptide sequencing, as well as bilateral co-immunoprecipitation to identify potentially interacting proteins in cervical-cancer cells. In this study, we proposed and successfully proved, for the first time, that CIP2A physically associates with H-Ras, which leads to the activation of the MEK/ERK signaling pathway and promotes EMT and cervical-cancer progression. Based on our observations and prior findings that CIP2A participates in c-Myc regulation, we conjecture that CIP2A may be a potentially promising molecular target for the adoptive therapy of human cancer.

Yuan J, Han B, Hu H, et al.
CUL4B activates Wnt/β-catenin signalling in hepatocellular carcinoma by repressing Wnt antagonists.
J Pathol. 2015; 235(5):784-95 [PubMed] Related Publications
Activation of Wnt/β-catenin signalling is frequently observed in many types of cancer including hepatocellular carcinoma (HCC). We recently reported that cullin 4B (CUL4B), a scaffold protein that assembles CRL4B ubiquitin ligase complexes, is overexpressed in many types of solid tumours and contributes to epigenetic silencing of tumour suppressors. In this study, we characterized the function of CUL4B in HCC and investigated whether CUL4B is involved in the regulation of Wnt/β-catenin signalling. CUL4B and β-catenin were frequently up-regulated and positively correlated in HCC tissues. CUL4B activated Wnt/β-catenin signalling by protecting β-catenin from GSK3-mediated degradation, achieved through CUL4B-mediated epigenetic silencing of Wnt pathway antagonists. Knockdown of CUL4B resulted in the up-regulation of Wnt signal antagonists such as DKK1 and PPP2R2B. Simultaneous knockdown of PPP2R2B partially reversed the down-regulation of β-catenin signalling caused by CUL4B depletion. Furthermore, CRL4B promoted the recruitment and/or retention of PRC2 at the promoters of Wnt antagonists and CUL4B knockdown decreased the retention of PRC2 components as well as H3K27me3. Knockdown of CUL4B reduced the proliferation, colony formation, and invasiveness of HCC cells in vitro and inhibited tumour growth in vivo, and these effects were attenuated by introduction of exogenous β-catenin or simultaneous knockdown of PPP2R2B. Conversely, ectopic expression of CUL4B enhanced the proliferation and invasiveness of HCC cells. We conclude that CUL4B can up-regulate Wnt/β-catenin signalling in human HCC through transcriptionally repressing Wnt antagonists and thus contributes to the malignancy of HCC.

Chun YJ
Knockdown of clusterin expression increases the in vitro sensitivity of human prostate cancer cells to paclitaxel.
J Toxicol Environ Health A. 2014; 77(22-24):1443-50 [PubMed] Related Publications
Clusterin/apolipoprotein J is a secreted heterodimeric glycoprotein that is implicated in several pathophysiological processes, including tissue remodeling, reproduction, lipid transport, and apoptosis. Although previous studies demonstrated that clusterin is able to protect against apoptosis, the role of the clusterin in cellular proliferation remains elusive. To determine whether clusterin plays an important role in cellular proliferation, the function of clusterin was examined using a small interfering RNA (siRNA) in PC3 human prostate cancer cells. Transient transfection with clusterin siRNA resulted in significant suppression of clusterin mRNA and protein expression. Clusterin knockdown resulted in a decrease in protein expression of phospho-Akt and an increase in expression of proteins phosphatase type 2AC (PP2AC) and phosphorylation of p38. However, treatment with PP2AC siRNA exerted minimal effects on clusterin expression. Interestingly, clusterin mRNA expression was reduced in paclitaxel-treated cells, and the cytotoxic effect of paclitaxel was more potent when cells were incubated with clusterin siRNA. In addition, co-treatment with paclitaxel and clusterin siRNA significantly enhanced PP2AC levels. Taken together, these results indicate that clusterin plays a crucial role in PC3 cell proliferation and that clusterin depletion may contribute to enhanced sensitivity of PC3 cells to anticancer agents such as paclitaxel.

Inoue D, Kitaura J, Matsui H, et al.
SETBP1 mutations drive leukemic transformation in ASXL1-mutated MDS.
Leukemia. 2015; 29(4):847-57 [PubMed] Related Publications
Mutations in ASXL1 are frequent in patients with myelodysplastic syndrome (MDS) and are associated with adverse survival, yet the molecular pathogenesis of ASXL1 mutations (ASXL1-MT) is not fully understood. Recently, it has been found that deletion of Asxl1 or expression of C-terminal-truncating ASXL1-MTs inhibit myeloid differentiation and induce MDS-like disease in mice. Here, we find that SET-binding protein 1 (SETBP1) mutations (SETBP1-MT) are enriched among ASXL1-mutated MDS patients and associated with increased incidence of leukemic transformation, as well as shorter survival, suggesting that SETBP1-MT play a critical role in leukemic transformation of MDS. We identify that SETBP1-MT inhibit ubiquitination and subsequent degradation of SETBP1, resulting in increased expression. Expression of SETBP1-MT, in turn, inhibited protein phosphatase 2A activity, leading to Akt activation and enhanced expression of posterior Hoxa genes in ASXL1-mutant cells. Biologically, SETBP1-MT augmented ASXL1-MT-induced differentiation block, inhibited apoptosis and enhanced myeloid colony output. SETBP1-MT collaborated with ASXL1-MT in inducing acute myeloid leukemia in vivo. The combination of ASXL1-MT and SETBP1-MT activated a stem cell signature and repressed the tumor growth factor-β signaling pathway, in contrast to the ASXL1-MT-induced MDS model. These data reveal that SETBP1-MT are critical drivers of ASXL1-mutated MDS and identify several deregulated pathways as potential therapeutic targets in high-risk MDS.

Li J, Yang XF, Ren XH, et al.
Stable SET knockdown in breast cell carcinoma inhibits cell migration and invasion.
Biochem Biophys Res Commun. 2014; 453(1):7-12 [PubMed] Related Publications
Breast cancer is the most malignant tumor for women, however, the mechanisms underlying this devastating disease remain unclear. SET is an endogenous inhibitor of protein phosphatase 2A (PP2A) and involved in many physiological and pathological processes. SET could promote the occurrence of tumor through inhibiting PP2A. In this study, we explore the role of SET in the migration and invasion of breast cancer cells MDA-MB-231 and ZR-75-30. The stable suppression of SET expression through lentivirus-mediated RNA interference (RNAi) was shown to inhibit the growth, migration and invasion of breast cancer cells. Knockdown of SET increases the activity and expression of PP2Ac and decrease the expression of matrix metalloproteinase 9 (MMP-9). These data demonstrate that SET may be involved in the pathogenic processes of breast cancer, indicating that SET can serve as a potential therapeutic target for the treatment of breast cancer.

Tan X, Chen M
MYLK and MYL9 expression in non-small cell lung cancer identified by bioinformatics analysis of public expression data.
Tumour Biol. 2014; 35(12):12189-200 [PubMed] Related Publications
Gene expression microarrays are widely used to investigate molecular targets in cancers, including lung cancer. In this study, we analyzed online non-small cell lung cancer (NSCLC) microarray databases, to screen the key genes and pathways related to NSCLC by bioinformatics analyses. And then, the expression levels of two selected genes in the down-regulated co-pathways, myosin light chain kinase (MYLK) and myosin regulatory light chain 9 (MYL9), were determined in tumor, paired paraneoplastic, and normal lung tissues. First, gene set enrichment analysis and meta-analysis were conducted to identify key genes and pathways that contribute to NSCLC carcinogenesis. Second, using the total RNA and protein extracted from lung cancer tissues (n = 240), adjacent non-cancer tissues (n = 240), and normal lung tissues (n = 300), we examined the MYLK and MYL9 expression levels by quantitative real-time PCR and Western blot. Finally, we explored the correlations between mRNA and protein expressions of these two genes and the clinicopathological parameters of NSCLC. Fifteen up-regulated and nine down-regulated co-pathways were observed. A number of differentially expressed genes (CALM1, THBS1, CSF3, BMP2, IL6ST, MYLK, ROCK2, IL3RA, MYL9, PPP2CA, CSF2RB, CNAQ, GRIA2, IL10RA, IL10RB, IL11RA, LIFR, PLCB4, and RAC3) were identified (P < 0.01) in the down-regulated co-pathways. The expression levels of MYLK and MYL9, which act downstream of the vascular smooth muscle contraction signal pathway and focal adhesion pathway, were significantly lower in cancer tissue than those in the paraneoplastic and normal tissues (P < 0.05). Moreover, the expression levels of these two genes in stages III and IV NSCLC were significantly increased, when compared to stages I and II, and expressions levels in NSCLC with lymphatic metastasis were higher than that without lymphatic metastasis (P < 0.05). Additionally, significant lower expression levels of the two genes were found in smokers than in nonsmokers (P < 0.05). In contrast, gender, differentiated degrees, and pathohistological type appeared to have no impact on these gene expressions (P > 0.05). These findings suggested that low MYLK and MYL9 expressions might be associated with the development of NSCLC. These genes may be also relevant to NSCLC metastasis. Future investigations with large sample sizes needed to verify these findings.

Qiu M, Liu L, Chen L, et al.
microRNA-183 plays as oncogenes by increasing cell proliferation, migration and invasion via targeting protein phosphatase 2A in renal cancer cells.
Biochem Biophys Res Commun. 2014; 452(1):163-9 [PubMed] Related Publications
The aim of this study was to investigate the function of miR-183 in renal cancer cells and the mechanisms miR-183 regulates this process. In this study, level of miR-183 in clinical renal cancer specimens was detected by quantitative real-time PCR. miR-183 was up- and down-regulated in two renal cancer cell lines ACHN and A498, respectively, and cell proliferation, Caspase 3/7 activity, colony formation, in vitro migration and invasion were measured; and then the mechanisms of miR-183 regulating was analyzed. We found that miR-183 was up-regulated in renal cancer tissues; inhibition of endogenous miR-183 suppressed in vitro cell proliferation, colony formation, migration, and invasion and stimulated Caspase 3/7 activity; up-regulated miR-183 increased cell growth and metastasis and suppressed Caspase 3/7 activity. We also found that miR-183 directly targeted tumor suppressor, specifically the 3'UTR of three subunits of protein phosphatase 2A (PP2A-Cα, PP2A-Cβ, and PP2A-B56-γ) transcripts, inhibiting their expression and regulated the downstream regulators p21, p27, MMP2/3/7 and TIMP1/2/3/4. These results revealed the oncogenes role of miR-183 in renal cancer cells via direct targeting protein phosphatase 2A.

Low IC, Loh T, Huang Y, et al.
Ser70 phosphorylation of Bcl-2 by selective tyrosine nitration of PP2A-B56δ stabilizes its antiapoptotic activity.
Blood. 2014; 124(14):2223-34 [PubMed] Related Publications
Bcl-2 is frequently overexpressed in hematopoietic malignancies, and selective phosphorylation at ser70 enhances its antiapoptotic activity. Phospho-ser70 is dephosphorylated by specific heterotrimers of protein phosphatase 2A (PP2A). We report here that a mild pro-oxidant intracellular milieu induced by either pharmacological inhibition or genetic knockdown of superoxide dismutase 1 (SOD1) inhibits the functional holoenzyme assembly of PP2A and prevents Bcl-2 ser70 dephosphorylation. This redox-dependent regulation of Bcl-2 phosphorylation is due to nitrosative modification of B56δ, which we identify as the regulatory subunit mediating PP2A-dependent Bcl-2 dephosphorylation. Redox inhibition of PP2A results from peroxynitrite-mediated nitration of a conserved tyrosine residue within B56δ (B56δ(Y289)). Although nitrated B56δ(Y289) binds efficiently to ser70-phosphorylated Bcl-2, this specific modification inhibits the recruitment of the PP2A catalytic core (A and C subunits). Furthermore, inhibition of B56δ(Y289) nitration restores PP2A holoenzyme assembly, thereby permitting S70 dephosphorylation of Bcl-2 and inhibiting its antiapoptotic activity. More important, in primary cells derived from clinical lymphomas, Bcl-2 phosphorylation at S70 directly correlates with B56δ nitration and repression of SOD1, but inversely correlates with B56δ interaction with the PP2A-C catalytic subunit. These data underscore the role of a pro-oxidant milieu in chemoresistance of hematopoietic and other cancers via selective targeting of tumor suppressors such as PP2A.

Yu HC, Hung MH, Chen YL, et al.
Erlotinib derivative inhibits hepatocellular carcinoma by targeting CIP2A to reactivate protein phosphatase 2A.
Cell Death Dis. 2014; 5:e1359 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
Protein phosphatase 2A (PP2A) is a tumor suppressor, which is functionally defective in various cancers. Previously, we found that PP2A activity determined the anticancer effect of bortezomib and erlotinib in hepatocellular carcinoma (HCC) cells. Here, we tested a novel erlotinib derivative, TD52, in four HCC cell lines, PLC5, Huh-7, Hep3B and Sk-Hep1. Using MTT and flow cytometry, we showed that TD52 had more potent apoptotic effects than erlotinib in HCC cells. TD52-induced apoptosis was associated with dose- and time- dependent reactivation of PP2A and downregulation of cancerous inhibitor of protein phosphatase 2A (CIP2A) and p-Akt. Inhibition of PP2A or ectopic expression of CIP2A or Akt in PLC5 cells abolished the effects of TD52. Furthermore, we demonstrated that TD52 affected the binding of Elk-1 to the proximal promoter of the CIP2A gene, thus downregulating transcription of CIP2A. Importantly, TD52-induced tumor inhibition was associated with reactivation of PP2A and downregulation of CIP2A and p-Akt in vivo. In conclusion, we found that enhancement of PP2A activity by inhibition of CIP2A determines the apoptotic effect induced by TD52. Our findings disclose the therapeutic mechanism of this novel targeted agent, and suggest the therapeutic potential and feasibility of developing PP2A enhancers as a novel anticancer strategy.

Wen X, Zhu J, Dong L, Chen Y
The role of c2orf68 and PI3K/Akt/mTOR pathway in human colorectal cancer.
Med Oncol. 2014; 31(8):92 [PubMed] Related Publications
The aim of the research is to determine whether c2orf68 gene plays a role in the carcinogenesis of human colorectal cancer and to study the function of c2orf68 belonging to the UPF0561 family. The mRNA expression levels of c2orf68 were examined in 30 pairs of human colorectal adenocarcinoma tissues and adjacent normal colorectal tissues by qRT-PCR. The SW480 and SW620 cell lines were transfected with siRNA against the c2orf68 gene and set gene. The expressed mRNA levels of Akt, PI3K, Bax, Bcl-2, caspase3, c-Myc, cyclinD1, pp2a and set were determined by qRT-PCR, and the protein levels of C2ORF68, c-Myc, PP2A and SET were examined by Western blot. Cell proliferation was tested by MTT assay, and apoptosis and cell cycle were studied by flow cytometry. Cancer metastasis assay was performed by transwell chamber. The c2orf68 mRNA expression was down-regulated in 63.33 % of the cancer samples, and a positive correlation was found between the mRNA expression of c-Myc and pp2a that of c2orf68. Meanwhile, there was a negative correlation between the mRNA expression of c2orf68 and set. The c2orf68 mRNA was significantly down-regulated in SW480(-c2orf68) and SW620(-c2orf68) cells. The inhibitory rate in the two cell lines was, respectively, 65.2 and 71.6 % by qRT-PCR. A 22.7 % inhibition on cell proliferation in SW480(-c2orf68) cells and a 21.2 % inhibition in SW620(-c2orf68) cells were observed using the MTT assay. Flow cytometry analysis indicates that the cell apoptosis rate was 21.42 % in SW480(-c2orf68) cells and 17.78 % in SW620(-c2orf68) cells, whereas the percentage of G1 phase cells was 61.8 and 58.6 % in SW480(-c2orf68) and SW620(-c2orf68) cells, respectively. In addition, the mRNA expression of set and Bax was up-regulated after c2orf68 interfered in SW480(-c2orf68) and SW620(-c2orf68) cells, whereas that of Bcl-2, c-Myc, cyclinD1, caspase3 and pp2a was down-regulated. Consistent with the mRNA results, the protein expression of C2ORF68, PP2A and c-Myc was down-regulated, whereas that of SET was up-regulated. Our data thus suggest that c2orf68 promotes carcinogenesis through the regulation of mammalian target of rapamycin signaling pathway.

De P, Carlson J, Leyland-Jones B, Dey N
Oncogenic nexus of cancerous inhibitor of protein phosphatase 2A (CIP2A): an oncoprotein with many hands.
Oncotarget. 2014; 5(13):4581-602 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
Oncoprotein CIP2A a Cancerous Inhibitor of PP2A forms an "oncogenic nexus" by virtue of its control on PP2A and MYC stabilization in cancer cells. The expression and prognostic function of CIP2A in different solid tumors including colorectal carcinoma, head and neck cancers, gastric cancers, lung carcinoma, cholangiocarcinoma, esophageal cancers, pancreatic carcinoma, brain cancers, breast carcinoma, bladder cancers, ovarian carcinoma, renal cell carcinomas, tongue cancers, cervical carcinoma, prostate cancers, and oral carcinoma as well as a number of hematological malignancies are just beginning to emerge. Herein, we reviewed the recent progress in our understanding of (1) how an "oncogenic nexus" of CIP2A participates in the tumorigenic transformation of cells and (2) how we can prospect/view the clinical relevance of CIP2A in the context of cancer therapy. The review will try to understand the role of CIP2A (a) as a biomarker in cancers and evaluate the prognostic value of CIP2A in different cancers (b) as a therapeutic target in cancers and (c) in drug response and developing chemo-resistance in cancers.

McDermott MS, Browne BC, Conlon NT, et al.
PP2A inhibition overcomes acquired resistance to HER2 targeted therapy.
Mol Cancer. 2014; 13:157 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
BACKGROUND: HER2 targeted therapies including trastuzumab and more recently lapatinib have significantly improved the prognosis for HER2 positive breast cancer patients. However, resistance to these agents is a significant clinical problem. Although several mechanisms have been proposed for resistance to trastuzumab, the mechanisms of lapatinib resistance remain largely unknown. In this study we generated new models of acquired resistance to HER2 targeted therapy and investigated mechanisms of resistance using phospho-proteomic profiling.
RESULTS: Long-term continuous exposure of SKBR3 cells to low dose lapatinib established a cell line, SKBR3-L, which is resistant to both lapatinib and trastuzumab. Phospho-proteomic profiling and immunoblotting revealed significant alterations in phospho-proteins involved in key signaling pathways and molecular events. In particular, phosphorylation of eukaryotic elongation factor 2 (eEF2), which inactivates eEF2, was significantly decreased in SKBR3-L cells compared to the parental SKBR3 cells. SKBR3-L cells exhibited significantly increased activity of protein phosphatase 2A (PP2A), a phosphatase that dephosphorylates eEF2. SKBR3-L cells showed increased sensitivity to PP2A inhibition, with okadaic acid, compared to SKBR3 cells. PP2A inhibition significantly enhanced response to lapatinib in both the SKBR3 and SKBR3-L cells. Furthermore, treatment of SKBR3 parental cells with the PP2A activator, FTY720, decreased sensitivity to lapatinib. The alteration in eEF2 phosphorylation, PP2A activity and sensitivity to okadaic acid were also observed in a second HER2 positive cell line model of acquired lapatinib resistance, HCC1954-L.
CONCLUSIONS: Our data suggests that decreased eEF2 phosphorylation, mediated by increased PP2A activity, contributes to resistance to HER2 inhibition and may provide novel targets for therapeutic intervention in HER2 positive breast cancer which is resistant to HER2 targeted therapies.

Mei Z, He Y, Feng J, et al.
MicroRNA-141 promotes the proliferation of non-small cell lung cancer cells by regulating expression of PHLPP1 and PHLPP2.
FEBS Lett. 2014; 588(17):3055-61 [PubMed] Related Publications
The dysregulation of microRNAs (miRNAs) is crucially implicated in the development of various cancers. In this study, we explored the biological role of miR-141 in non-small cell lung cancer (NSCLC). miR-141 expression was significantly up-regulated in NSCLC tissues, and its overexpression accelerated NSCLC cell proliferation in vitro and tumor growth in vivo. We subsequently identified the antagonists of PI3K/AKT signaling, PH domain leucine-rich-repeats protein phosphatase 1 (PHLPP1) and PHLPP2, as direct targets of miR-141. Re-introduction of PHLPP1 and PHLPP2 abrogated miR-141-induced proliferation of NSCLC cells. Together, the results of this study suggest that miR-141 and its targets PHLPP1 and PHLPP2 play critical roles in NSCLC tumorigenesis, and provide potential therapeutic targets for NSCLC treatment.

Nifoussi SK, Ratcliffe NR, Ornstein DL, et al.
Inhibition of protein phosphatase 2A (PP2A) prevents Mcl-1 protein dephosphorylation at the Thr-163/Ser-159 phosphodegron, dramatically reducing expression in Mcl-1-amplified lymphoma cells.
J Biol Chem. 2014; 289(32):21950-9 [PubMed] Article available free on PMC after 08/08/2015 Related Publications
Abundant, sustained expression of prosurvival Mcl-1 is an important determinant of viability and drug resistance in cancer cells. The Mcl-1 protein contains PEST sequences (enriched in proline, glutamic acid, serine, and threonine) and is normally subject to rapid turnover via multiple different pathways. One of these pathways involves a phosphodegron in the PEST region, where Thr-163 phosphorylation primes for Ser-159 phosphorylation by glycogen synthase kinase-3. Turnover via this phosphodegron-targeted pathway is reduced in Mcl-1-overexpressing BL41-3 Burkitt lymphoma and other cancer cells; turnover is further slowed in the presence of phorbol ester-induced ERK activation, resulting in Mcl-1 stabilization and an exacerbation of chemoresistance. The present studies focused on Mcl-1 dephosphorylation, which was also found to profoundly influence turnover. Exposure of BL41-3 cells to an inhibitor of protein phosphatase 2A (PP2A), okadaic acid, resulted in a rapid increase in phosphorylation at Thr-163 and Ser-159, along with a precipitous decrease in Mcl-1 expression. The decline in Mcl-1 expression preceded the appearance of cell death markers and was not slowed in the presence of phorbol ester. Upon exposure to calyculin A, which also potently inhibits PP2A, versus tautomycin, which does not, only the former increased Thr-163/Ser-159 phosphorylation and decreased Mcl-1 expression. Mcl-1 co-immunoprecipitated with PP2A upon transfection into CHO cells, and PP2A/Aα knockdown recapitulated the increase in Mcl-1 phosphorylation and decrease in expression. In sum, inhibition of PP2A prevents Mcl-1 dephosphorylation and results in rapid loss of this prosurvival protein in chemoresistant cancer cells.

Janghorban M, Farrell AS, Allen-Petersen BL, et al.
Targeting c-MYC by antagonizing PP2A inhibitors in breast cancer.
Proc Natl Acad Sci U S A. 2014; 111(25):9157-62 [PubMed] Article available free on PMC after 08/08/2015 Related Publications
The transcription factor c-MYC is stabilized and activated by phosphorylation at serine 62 (S62) in breast cancer. Protein phosphatase 2A (PP2A) is a critical negative regulator of c-MYC through its ability to dephosphorylate S62. By inactivating c-MYC and other key signaling pathways, PP2A plays an important tumor suppressor function. Two endogenous inhibitors of PP2A, I2PP2A, Inhibitor-2 of PP2A (SET oncoprotein) and cancerous inhibitor of PP2A (CIP2A), inactivate PP2A and are overexpressed in several tumor types. Here we show that SET is overexpressed in about 50-60% and CIP2A in about 90% of breast cancers. Knockdown of SET or CIP2A reduces the tumorigenic potential of breast cancer cell lines both in vitro and in vivo. Treatment of breast cancer cells in vitro or in vivo with OP449, a novel SET antagonist, also decreases the tumorigenic potential of breast cancer cells and induces apoptosis. We show that this is, at least in part, due to decreased S62 phosphorylation of c-MYC and reduced c-MYC activity and target gene expression. Because of the ubiquitous expression and tumor suppressor activity of PP2A in cells, as well as the critical role of c-MYC in human cancer, we propose that activation of PP2A (here accomplished through antagonizing endogenous inhibitors) could be a novel antitumor strategy to posttranslationally target c-MYC in breast cancer.

Wu MY, Xie X, Xu ZK, et al.
PP2A inhibitors suppress migration and growth of PANC-1 pancreatic cancer cells through inhibition on the Wnt/β-catenin pathway by phosphorylation and degradation of β-catenin.
Oncol Rep. 2014; 32(2):513-22 [PubMed] Article available free on PMC after 08/08/2015 Related Publications
Cantharidin is an active constituent of mylabris, a traditional Chinese medicine, and presents strong anticancer activity in various cell lines. Cantharidin is a potent and selective inhibitor of serine/threonine protein phosphatase 2A (PP2A). Our previous studies revealed the prospect of application of cantharidin, as well as other PP2A inhibitors, in the treatment of pancreatic cancer. However, the mechanisms involved in the anticancer effect of PP2A inhibitors have not been fully explored. The Wnt/β‑catenin pathway is involved in cell migration and proliferation and participates in the progression of pancreatic cancer. If β‑catenin is phosphorylated and degraded, the Wnt/β‑catenin pathway is blocked. PP2A dephosphorylates β‑catenin and keeps the Wnt/β‑catenin pathway active. In the present study, we found that PP2A inhibitor treatment induced phosphorylation and degradation of β‑catenin. The suppression on the migration and growth of PANC‑1 pancreatic cancer cells could be attenuated by pretreatment with FH535, a β‑catenin pathway inhibitor. Microarray showed that PP2A inhibitor treatment induced expression changes in 13 of 138 genes downstream of the β‑catenin pathway. Real‑time PCR further confirmed that FH535 attenuated the expression changes induced by PP2A inhibitors in 6 of these 13 candidate genes. These 6 genes, VEGFB, Dkk3, KRT8, NRP1, Cacnalg and WISP2, have been confirmed to participate in the migration and/or growth regulation in previous studies. Thus, the phosphorylation- and degradation-mediated suppression on β‑catenin participates in the cytotoxicity of PP2A inhibitors. Our findings may provide insight into the treatment of pancreatic cancer using a targeting PP2A strategy.

Lee YH, Morrison BL, Bottaro DP
Synergistic signaling of tumor cell invasiveness by hepatocyte growth factor and hypoxia.
J Biol Chem. 2014; 289(30):20448-61 [PubMed] Article available free on PMC after 25/07/2015 Related Publications
Hepatocyte growth factor (HGF) signaling promotes tumor invasiveness in renal cell carcinoma (RCC) and other cancers. In clear cell RCC, VHL loss generates pseudohypoxia that exacerbates HGF-driven invasion through β-catenin deregulation. Hypoxia also enhances HGF-driven invasiveness by papillary RCC cells, but in the absence of VHL, loss signaling integration involves three parallel routes: 1) hypoxia-induced reactive oxygen species production and decreased DUSP2 expression, leading to enhanced mitogen-activated protein kinase (MAPK) cascade activation; 2) reactive oxygen species-induced diacylglycerol production by phospholipase Cγ, leading to protein kinase C activation and increased protein phosphatase- 2A activity, thereby suppressing HGF-induced Akt activation; and 3) a profound shift from HGF-enhanced, proliferation- oriented metabolism to autophagy-dependent invasion and suppression of proliferation. This tripartite signaling integration was not unique to RCC or HGF; in RCC cells, invasive synergy induced by the combination of hypoxia and epidermal growth factor occurred through the same mechanism, and in estrogen receptor-positive breast cancer cells, this mechanism was suppressed in the absence of estrogen. These results define the molecular basis of growth factor and hypoxia invasive synergy in VHL-competent papillary RCC cells, illustrate the plasticity of invasive and proliferative tumor cell states, and provide signaling profiles by which they may be predicted.

Ruvolo PP, Ruvolo VR, Jacamo R, et al.
The protein phosphatase 2A regulatory subunit B55α is a modulator of signaling and microRNA expression in acute myeloid leukemia cells.
Biochim Biophys Acta. 2014; 1843(9):1969-77 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
We recently discovered that the protein phosphatase 2A (PP2A) B55α subunit (PPP2R2A) is under-expressed in primary blast cells and is unfavorable for remission duration in AML patients. In this study, reverse phase protein analysis (RPPA) of 230 proteins in 511 AML patient samples revealed a strong correlation of B55α with a number of proteins including MYC, PKC α, and SRC. B55α suppression in OCI-AML3 cells by shRNA demonstrated that the B subunit is a PKCα phosphatase. B55α does not target SRC, but rather the kinase suppresses protein expression of the B subunit. Finally, the correlation between B55α and MYC levels reflected a complex stoichiometric competition between B subunits. Loss of B55α in OCI-AML3 cells did not change global PP2A activity and the only isoform that is induced is the one containing B56α. In cells containing B55α shRNA, MYC was suppressed with concomitant induction of the competing B subunit B56α (PPP2R5A). A recent study determined that FTY-720, a drug whose action involves the activation of PP2A, resulted in the induction of B55α In AML cells, and a reduction of the B subunit rendered these cells resistant to FTY-720. Finally, reduction of the B subunit resulted in an increase in the expression of miR-191-5p and a suppression of miR-142-3p. B55α regulation of these miRs was intriguing as high levels of miR-191 portend poor survival in AML, and miR-142-3p is mutated in 2% of AML patient samples. In summary, the suppression of B55α activates signaling pathways that could support leukemia cell survival.

Luo DJ, Feng Q, Wang ZH, et al.
Knockdown of phosphotyrosyl phosphatase activator induces apoptosis via mitochondrial pathway and the attenuation by simultaneous tau hyperphosphorylation.
J Neurochem. 2014; 130(6):816-25 [PubMed] Related Publications
Phosphotyrosyl phosphatase activator (PTPA) is decreased in the brains of Alzheimer's disease (AD) and the AD transgenic mouse models. Here, we investigated whether down-regulation of PTPA affects cell viability and the underlying mechanisms. We found that PTPA was located in the integral membrane of mitochondria, and knockdown of PTPA induced cell apoptosis in HEK293 and N2a cell lines. PTPA knockdown decreased mitochondrial membrane potential and induced Bax translocation into the mitochondria with a simultaneous release of Cyt C, activation of caspase-3, cleavage of poly (DNA ribose) polymerase (PARP), and decrease in Bcl-xl and Bcl-2 protein levels. Over-expression of Protein phosphatase 2A (PP2A) catalytic subunit (PP2AC ) did not rescue the apoptosis induced by PTPA knockdown, and PTPA knockdown did not affect the level of and their phosphorylation of mitogen-activated protein kinases (MAPKs), indicating that PP2A and MAPKs were not involved in the apoptosis induced by PTPA knockdown. In the cells with over-expression of tau, PTPA knockdown induced PP2A inhibition and tau hyperphosphorylation but did not cause significant cell death. These data suggest that PTPA deficit causes apoptotic cell death through mitochondrial pathway and simultaneous tau hyperphosphorylation attenuates the PTPA-induced cell death. Phosphotyrosyl phosphatase activator (PTPA) is decreased in the brains of Alzheimer's disease (AD) and AD transgenic mouse models. Here, we investigated whether down-regulation of PTPA affects cell viability. We found that PTPA located in the integral membrane of mitochondria, and knockdown of PTPA induced cell apoptosis in HEK293 and N2a cell lines by decreasing mitochondrial membrane potential, which leads to translocation of Bax and a simultaneous release of Cyt C. In the cells with tau over-expression, PTPA knockdown inactivated PP2A to phosphorylate tau to avoid cell apoptosis which induced by PTPA knockdown.

Preuss KD, Fadle N, Regitz E, et al.
Inactivation of protein-phosphatase 2A causing hyperphosphorylation of autoantigenic paraprotein targets in MGUS/MM is due to an exchange of its regulatory subunits.
Int J Cancer. 2014; 135(9):2046-53 [PubMed] Related Publications
Hyperphosphorylated paratarg-7 (pP-7) carrier state is the strongest molecularly defined risk factor for monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM). pP-7 is inherited as autosomal-dominant trait and depending on the ethnic background is found in over one-third of MGUS/MM patients. P-7, which is the antigenic paraprotein target in these patients, is hyperphosphorylated at serine17. P-7 hyperphosphorylation can be induced in wild-type P-7 (wtP-7) carriers by PKCζ and reverted by protein-phosphatase 2A (PP2A). Here we show that dephosphorylation of pP-7 is defective in pP-7 carriers due to inactivation of the PP2A by substitution of the regulatory B55δ subunit with B56γ3. In lymphoblastoid cell lines from pP-7 carriers, transfection of recombinant B55δ or treatment with ceramide led to a partial reconstitution of PP2A activity and dephosphorylation of pP-7 to wtP7. Similar results were observed with other previously reported autoantigenic paraproteins targets. In conclusion, the mechanisms responsible for the defective dephosphorylation and maintaining the hyperphosphorylated state of P-7 and other autoantigenic paraprotein targets have been elucidated, facilitating the identification of the genetic basis underlying this phenomenon which is obviously common in the pathogenesis of MGUS/MM/WM and not restricted to pP-7 cases.

Farrell AS, Allen-Petersen B, Daniel CJ, et al.
Targeting inhibitors of the tumor suppressor PP2A for the treatment of pancreatic cancer.
Mol Cancer Res. 2014; 12(6):924-39 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
UNLABELLED: Pancreatic cancer is a deadly disease that is usually diagnosed in the advanced stages when few effective therapies are available. Given the aggressive clinical course of this disease and lack of good treatment options, the development of new therapeutic agents for the treatment of pancreatic cancer is of the upmost importance. Several pathways that have shown to contribute to pancreatic cancer progression are negatively regulated by the tumor suppressor protein phosphatase 2A (PP2A). Here, the endogenous inhibitors of PP2A, SET (also known as I2PP2A) and cancerous inhibitor of PP2A (CIP2A), were shown to be overexpressed in human pancreatic cancer, contributing to decreased PP2A activity and overexpression and stabilization of the oncoprotein c-Myc, a key PP2A target. Knockdown of SET or CIP2A increases PP2A activity, increases c-Myc degradation, and decreases the tumorigenic potential of pancreatic cancer cell lines both in vitro and in vivo. Moreover, treatment with a novel SET inhibitor, OP449, pharmacologically recapitulates the phenotypes and significantly reduces proliferation and tumorigenic potential of several pancreatic cancer cell lines, with an accompanying attenuation of cell growth and survival signaling. Furthermore, primary cells from patients with pancreatic cancer were sensitive to OP449 treatment, indicating that PP2A-regulated pathways are highly relevant to this deadly disease.
IMPLICATIONS: The PP2A inhibitors SET and CIP2A are overexpressed in human pancreatic cancer and are important for pancreatic cancer cell growth and transformation; thus, antagonizing SET and/or CIP2A may be an innovative approach for the treatment of human pancreatic cancer.

Bhardwaj A, Singh S, Srivastava SK, et al.
Restoration of PPP2CA expression reverses epithelial-to-mesenchymal transition and suppresses prostate tumour growth and metastasis in an orthotopic mouse model.
Br J Cancer. 2014; 110(8):2000-10 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
BACKGROUND: Emergence of castration-resistance in prostate cancer (PCa) is invariably associated with aggressive and metastatic disease. Previously, we reported promotion of castration-resistance upon downregulation of PPP2CA (encoding catalytic subunit of protein phosphatase 2A (PP2A), α-isoform); however, its role in PCa growth and metastasis remained undetermined.
METHODS: PPP2CA was overexpressed/silenced in PCa cells by stable transfection. Gene expression was examined by reverse transcription polymerase chain reaction, immunoblot and immunofluorescence analyses, and transcriptional activity measured by luciferase-based promoter-reporter assay. Effect on PCa phenotype was studied in vitro and in orthotopic mouse model, and immunohistochemical/histological analyses performed to assess proliferation/apoptosis and confirm metastatic lesions.
RESULTS: An inverse association of PPP2CA expression was observed with epithelial-to-mesenchymal transition (EMT) and aggressive PCa phenotype. PPP2CA restoration resulted in decreased nuclear accumulation and transcriptional activity of β-catenin/NF-κB, and restitution of their activity abrogated PPP2CA-induced EMT reversal and suppression of PCa invasiveness. Akt mediated PPP2CA loss-induced nuclear accumulation of β-catenin/NF-κB through inactivation of Gsk3-β and IκB-α, respectively. Animal studies revealed a suppressive effect of PPP2CA expression on PCa growth and metastasis.
CONCLUSIONS: Our findings suggest that PPP2CA downregulation serves as a molecular link between gain of castration-resistance and aggressive PCa phenotype, and its restoration could be an effective preventive/therapeutic approach against the advanced disease.

Gilan O, Diesch J, Amalia M, et al.
PR55α-containing protein phosphatase 2A complexes promote cancer cell migration and invasion through regulation of AP-1 transcriptional activity.
Oncogene. 2015; 34(10):1333-9 [PubMed] Related Publications
The proto-oncogene c-Jun is a component of activator protein-1 (AP-1) transcription factor complexes that regulates processes essential for embryonic development, tissue homeostasis and malignant transformation. Induction of gene expression by c-Jun involves stimulation of its transactivation ability and upregulation of DNA binding capacity. While it is well established that the former requires JNK-mediated phosphorylation of S63/S73, the mechanism(s) through which binding of c-Jun to its endogenous target genes is regulated remains poorly characterized. Here we show that interaction of c-Jun with chromatin is positively regulated by protein phosphatase 2A (PP2A) complexes targeted to c-Jun by the PR55α regulatory subunit. PR55α-PP2A specifically dephosphorylates T239 of c-Jun, promoting its binding to genes regulating tumour cell migration and invasion. PR55α-PP2A also enhanced transcription of these genes, without affecting phosphorylation of c-Jun on S63. These findings suggest a critical role for interplay between JNK and PP2A pathways determining the functional activity of c-Jun/AP-1 in tumour cells.

Kubota D, Yoshida A, Kawai A, Kondo T
Proteomics identified overexpression of SET oncogene product and possible therapeutic utility of protein phosphatase 2A in alveolar soft part sarcoma.
J Proteome Res. 2014; 13(5):2250-61 [PubMed] Related Publications
Alveolar soft part sarcoma (ASPS) is an exceedingly rare sarcoma refractory to standard chemotherapy. Although several molecular targeting drugs have been applied for ASPS, their clinical significance has not yet been established, and novel therapeutic strategies have long been required. The aim of this study was to identify proteins aberrantly regulated in ASPS and to clarify their clinical significance. Protein expression profiling of tumor and nontumor tissues from 12 ASPS patients was performed by 2-D difference gel electrophoresis and mass spectrometry. We found that the expression of 145 proteins differed significantly. Among them, further investigation was focused on the SET protein, which has multifunctional roles in cancers. Immunohistochemistry confirmed overexpression of SET in all 15 ASPS cases examined. Gene silencing of SET significantly decreased cell proliferation, invasion, and migration against a background of induced apoptosis. SET is known to be an inhibitor of phosphatase 2A (PP2A), which functions as a tumor suppressor by inhibiting the signal transduction pathway and inducing apoptosis. We found that a PP2A activator, FTY720, decreased cell proliferation through apoptosis. Together, our findings may suggest the possible contribution of SET to the tumor progression and the utility of FTY720 for treatment of ASPS.

Activation of PP2A by perphenazine induces apoptosis in T-ALL.
Cancer Discov. 2014; 4(3):OF14 [PubMed] Related Publications
Drug repurposing screens identify the antipsychotic agent perphenazine as active against T-ALL.

Cho EA, Kim EJ, Kwak SJ, Juhnn YS
cAMP signaling inhibits radiation-induced ATM phosphorylation leading to the augmentation of apoptosis in human lung cancer cells.
Mol Cancer. 2014; 13:36 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
BACKGROUND: The ataxia-telangiectasia mutated (ATM) protein kinase plays a central role in coordinating the cellular response to radiation-induced DNA damage. cAMP signaling regulates various cellular responses including metabolism and gene expression. This study aimed to investigate the mechanism through which cAMP signaling regulates ATM activation and cellular responses to ionizing radiation in lung cancer cells.
METHODS: Lung cancer cells were transfected with constitutively active stimulatory G protein (GαsQL), and irradiated with γ-rays. The phosphorylation of ATM and protein phosphatase 2A was analyzed by western blotting, and apoptosis was assessed by western blotting, flow cytometry, and TUNNEL staining. The promoter activity of NF-κB was determined by dual luciferase reporter assay. BALB/c mice were treated with forskolin to assess the effect in the lung tissue.
RESULTS: Transient expression of GαsQL significantly inhibited radiation-induced ATM phosphorylation in H1299 human lung cancer cells. Treatment with okadaic acid or knock down of PP2A B56δ subunit abolished the inhibitory effect of Gαs on radiation-induced ATM phosphorylation. Expression of GαsQL increased phosphorylation of the B56δ and PP2A activity, and inhibition of PKA blocked Gαs-induced PP2A activation. GαsQL enhanced radiation-induced cleavage of caspase-3 and PARP and increased the number of early apoptotic cells. The radiation-induced apoptosis was increased by inhibition of NF-κB using PDTC or inhibition of ATM using KU55933 or siRNA against ATM. Pretreatment of BALB/c mice with forskolin stimulated phosphorylation of PP2A B56δ, inhibited the activation of ATM and NF-κB, and augmented radiation-induced apoptosis in the lung tissue. GαsQL expression decreased the nuclear levels of the p50 and p65 subunits and NF-κB-dependent activity after γ-ray irradiation in H1299 cells. Pretreatment with prostaglandin E2 or isoproterenol increased B56δ phosphorylation, decreased radiation-induced ATM phosphorylation and increased apoptosis.
CONCLUSIONS: cAMP signaling inhibits radiation-induced ATM activation by PKA-dependent activation of PP2A, and this signaling mechanism augments radiation-induced apoptosis by reducing ATM-dependent activation of NF-κB in lung cancer cells.

Zou Y, Liu FY, Liu H, et al.
Frequent POLE1 p.S297F mutation in Chinese patients with ovarian endometrioid carcinoma.
Mutat Res. 2014; 761:49-52 [PubMed] Related Publications
The catalytic subunit of DNA polymerase epsilon (POLE1) functions primarily in nuclear DNA replication and repair. Recently, POLE1 mutations were detected frequently in colorectal and endometrial carcinomas while with lower frequency in several other types of cancer, and the p.P286R and p.V411L mutations were the potential mutation hotspots in human cancers. Nevertheless, the mutation frequency of POLE1 in ovarian cancer still remains largely unknown. Here, we screened a total of 251 Chinese samples with distinct subtypes of ovarian carcinoma for the presence of POLE1 hotspot mutations by direct sequencing. A heterozygous somatic POLE1 mutation, p.S297F (c.890C>T), but not p.P286R and p.V411L hotspot mutations observed in other cancer types, was identified in 3 out of 37 (8.1%) patients with ovarian endometrioid carcinoma; this mutation was evolutionarily highly conserved from Homo sapiens to Schizosaccharomyces. Of note, the POLE1 mutation coexisted with mutation in the ovarian cancer-associated PPP2R1A (protein phosphatase 2, regulatory subunit A, α) gene in a 46-year-old patient, who was also diagnosed with ectopic endometriosis in the benign ovary. In addition, a 45-year-old POLE1-mutated ovarian endometrioid carcinoma patient was also diagnosed with uterine leiomyoma while the remaining 52-year-old POLE1-mutated patient showed no additional distinctive clinical manifestation. In contrast to high frequency of POLE1 mutations in ovarian endometrioid carcinoma, no POLE1 mutations were identified in patients with other subtypes of ovarian carcinoma. Our results showed for the first time that the POLE1 p.S297F mutation, but not p.P286R and p.V411L hotspot mutations observed in other cancer types, was frequent in Chinese ovarian endometrioid carcinoma, but absent in other subtypes of ovarian carcinoma. These results implicated that POLE1 p.S297F mutation might be actively involved in the pathogenesis of ovarian endometrioid carcinoma, but might not be actively involved in other subtypes of ovarian carcinoma.

Bera R, Chiou CY, Yu MC, et al.
Functional genomics identified a novel protein tyrosine phosphatase receptor type F-mediated growth inhibition in hepatocarcinogenesis.
Hepatology. 2014; 59(6):2238-50 [PubMed] Related Publications
UNLABELLED: It is unclear how proliferating cells elicit suppression on cell proliferation and how cancer cells evade this growth suppression. Using a loss-of-function screening of the human kinome and phosphatome to identify genes suppressing tumor initiation in human hepatocellular carcinoma (HCC), we identified 19 genes and characterized one of the top-scoring tumor suppressor candidates, protein tyrosine phosphatase receptor type F (PTPRF). We found that PTPRF was induced during cell proliferation by cell-cell contact. Ectopic expression of wild-type PTPRF, but not the phosphatase-inactive mutant, suppressed cell proliferation and colony formation in soft-agar assays. In contrast, PTPRF silencing led to cell hyperproliferation, enhanced tumor colony formation in soft agar, and increased xenograft tumor growth in nude mice. Mechanistically, PTPRF silencing showed aberrant ERK-dependent signaling including the phosphorylation/stabilization of v-myc avian myelocytomatosis viral oncogene homolog (MYC) through the direct activation of v-src avian sarcoma viral oncogene homolog (SRC) and suppression of PP2A. This PTPRF-mediated growth suppression during cell proliferation functioned independently of the Hippo-Yap pathway. Clinically, PTPRF was down-regulated in 42% HCC (37/89), 67% gastric cancer (27/40), and 100% colorectal cancer (40/40). PTPRF up-regulation was found in 24% HCC (21/89) and associated with better clinical outcomes.
CONCLUSION: A novel PTPRF-mediated growth suppression pathway was identified by way of a functional genomics screening in human hepatoma cells. Induction of PTPRF by cell-cell contact during cell proliferation quenched the activated ERK-dependent proliferation signaling to prevent cell hyperproliferation and tumor initiation. PTPRF down-regulation in HCC facilitated tumor development. Our findings shed light on how cancer cells can evade growth suppression and open a new avenue for future development of anticancer therapies.

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Cite this page: Cotterill SJ. PPP2CA, Cancer Genetics Web: http://www.cancer-genetics.org/PPP2CA.htm Accessed:

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