Gene Summary

Gene:PAK1; p21 protein (Cdc42/Rac)-activated kinase 1
Aliases: PAKalpha
Summary:This gene encodes a family member of serine/threonine p21-activating kinases, known as PAK proteins. These proteins are critical effectors that link RhoGTPases to cytoskeleton reorganization and nuclear signaling, and they serve as targets for the small GTP binding proteins Cdc42 and Rac. This specific family member regulates cell motility and morphology. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Apr 2010]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:serine/threonine-protein kinase PAK 1
Source:NCBIAccessed: 27 February, 2015


What does this gene/protein do?
Show (44)
Pathways:What pathways are this gene/protein implicaed in?
Show (19)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 27 February 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.

  • Neoplasm Invasiveness
  • PAK1 protein, human
  • Neoplasm Proteins
  • MAP Kinase Signaling System
  • rac GTP-Binding Proteins
  • p21-Activated Kinases
  • rho-Associated Kinases
  • Tissue Array Analysis
  • Neoplasm Metastasis
  • Signal Transduction
  • Breast Cancer
  • Mutation
  • CDC42
  • RHOA
  • Cell Movement
  • Neurofibromatosis 2
  • Cancer Gene Expression Regulation
  • Neoplastic Cell Transformation
  • Apoptosis
  • Gene Amplification
  • Ovarian Cancer
  • siRNA
  • Transcription Factors
  • Chromosome 11
  • Cell Proliferation
  • Cyclin D1
  • FISH
  • Staging
  • Enzyme Activation
  • Messenger RNA
  • Phosphorylation
  • Gene Expression Profiling
  • Immunohistochemistry
  • rho GTP-Binding Proteins
  • Drug Resistance
  • Oligonucleotide Array Sequence Analysis
  • Western Blotting
  • Transfection
  • Protein-Serine-Threonine Kinases
Tag cloud generated 27 February, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (2)

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: PAK1 (cancer-related)

Ergun S, Tayeb TS, Arslan A, et al.
The investigation of miR-221-3p and PAK1 gene expressions in breast cancer cell lines.
Gene. 2015; 555(2):377-81 [PubMed] Related Publications
The most common malignancy in women is breast cancer. Drug resistance in the treatment of cancer still remains a major clinical concern. Resistance to tamoxifen is seen in half of the recurrences in breast cancer. The anti-estrogen tamoxifen gains agonistic property by transactivating ERα. PAK1-mediated phosphorylation of serine 305 (S305) of ERα leads to resistance to tamoxifen. In our study, PAK1-induced suggestive tamoxifen resistance was designed. According to our hypothesis, phosphorylation of ERα-S305 by PAK1 may be reversed by PAK1 transcriptional inhibition by miR-221-3p due to miR-221-3p targeting the 3' UTR of PAK1. For this purpose, we used Real-time PCR (qRT-PCR) to measure the expression level of miR-221-3p in ER-positive breast cancer cell lines (ZR-75-1, MCF7) and breast epithelial cell line, hTERT-HME1, as control in the laboratory in our department. The increase in the expression of PAK1 depending on miR-221-3p may be related to ZR-75-1 cell line which has invasive characteristic but other two ER+ cancer cell lines, MCF7 and HCC1500, have milder cancer severity. miR-221-3p may have a role on regulation of PAK1 expression because miR-221-3p expression level decreases while PAK1 expression level increases in SKBR3 cell line. miR-221-3p and PAK1 expressions in MDA-MB-231 cell line are higher than that of hTERT-HME1 cell line. This may mean that miR-221-3p has no regulatory effect on of PAK1 expression in this cell line. According to these results, miR-221-3p may give crucial information about molecular mechanism of the disease upon PAK1 activity or different mechanisms with respect to histopathology and severity of breast cancer.

Cai K, Mulatz K, Ard R, et al.
Increased diacylglycerol kinase ζ expression in human metastatic colon cancer cells augments Rho GTPase activity and contributes to enhanced invasion.
BMC Cancer. 2014; 14:208 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Unraveling the signaling pathways responsible for the establishment of a metastatic phenotype in carcinoma cells is critically important for understanding the pathology of cancer. The acquisition of cell motility is a key property of metastatic tumor cells and is a prerequisite for invasion. Rho GTPases regulate actin cytoskeleton reorganization and the cellular responses required for cell motility and invasion. Diacylglycerol kinase ζ (DGKζ), an enzyme that phosphorylates diacylglycerol to yield phosphatidic acid, regulates the activity of the Rho GTPases Rac1 and RhoA. DGKζ mRNA is highly expressed in several different colon cancer cell lines, as well as in colon cancer tissue relative to normal colonic epithelium, and thus may contribute to the metastatic process.
METHODS: To investigate potential roles of DGKζ in cancer metastasis, a cellular, isogenic model of human colorectal cancer metastatic transition was used. DGKζ protein levels, Rac1 and RhoA activity, and PAK phosphorylation were measured in the non-metastatic SW480 adenocarcinoma cell line and its highly metastatic variant, the SW620 line. The effect of DGKζ silencing on Rho GTPase activity and invasion through Matrigel-coated Transwell inserts was studied in SW620 cells. Invasiveness was also measured in PC-3 prostate cancer and MDA-MB-231 breast cancer cells depleted of DGKζ.
RESULTS: DGKζ protein levels were elevated approximately 3-fold in SW620 cells compared to SW480 cells. There was a concomitant increase in active Rac1 in SW620 cells, as well as substantial increases in the expression and phosphorylation of the Rac1 effector PAK1. Similarly, RhoA activity and expression were increased in SW620 cells. Knockdown of DGKζ expression in SW620 cells by shRNA-mediated silencing significantly reduced Rac1 and RhoA activity and attenuated the invasiveness of SW620 cells in vitro. DGKζ silencing in highly metastatic MDA-MB-231 breast cancer cells and PC-3 prostate cancer cells also significantly attenuated their invasiveness.
CONCLUSION: Elevated DGKζ expression contributes to increased Rho GTPase activation and the enhanced motility of metastatic cancer cells. These findings warrant further investigation of the clinical relevance of DGKζ upregulation in colon and other cancers. Interfering with DGKζ function could provide a means of inhibiting invasion and metastasis.

Chen QY, Zheng Y, Jiao DM, et al.
Curcumin inhibits lung cancer cell migration and invasion through Rac1-dependent signaling pathway.
J Nutr Biochem. 2014; 25(2):177-85 [PubMed] Related Publications
Curcumin, a natural and crystalline compound isolated from the plant Curcuma longa with low toxicity in normal cells, has been shown to protect against carcinogenesis and prevent tumor development. However, little is known about antimetastasis effects and mechanism of curcumin in lung cancer. Rac1 is an important small Rho GTPases family protein and has been widely implicated in cytoskeleton rearrangements and cancer cell migration, invasion and metastasis. In this study, we examined the influence of curcumin on in vitro invasiveness of human lung cancer cells and the expressions of Rac1. The results indicate that curcumin at 10 μM slightly reduced the proliferation of 801D lung cancer cells but showed an obvious inhibitory effect on epidermal growth factor or transforming growth factor β1-induced lung cancer cell migration and invasion. Meanwhile, we demonstrated that the suppression of invasiveness correlated with inhibition of Rac1/PAK1 signaling pathways and matrix metalloproteinase (MMP) 2 and 9 protein expression by combining curcumin treatment with the methods of Rac1 gene silence and overexpression in lung cancer cells. Laser confocal microscope also showed that Rac1-regulated actin cytoskeleton rearrangement may be involved in anti-invasion effect of curcumin on lung cancer cell. At last, through xenograft experiments, we confirmed the connection between Rac1 and the growth and metastasis inhibitory effect of curcumin in vivo. In summary, these data demonstrated that low-toxic levels of curcumin could efficiently inhibit migration and invasion of lung cancer cells through inhibition of Rac1/PAK1 signaling pathway and MMP-2 and MMP-9 expression, which provided a novel insight into the molecular mechanism of curcumin against lung cancer.

Xu J, Jia L, Ma H, et al.
Axl gene knockdown inhibits the metastasis properties of hepatocellular carcinoma via PI3K/Akt-PAK1 signal pathway.
Tumour Biol. 2014; 35(4):3809-17 [PubMed] Related Publications
The objective of this study is to clarify the possible role and mechanism of Axl in the tumorigenicity and metastasis process of hepatocellular carcinoma. The mRNA and protein expression levels of Axl in MHCC97-H and MHCC97-L cell lines were evaluated by real-time PCR and Western blot analysis. The key factor of phosphatidylinositol-3-kinase (PI3K)/Akt-p21-activated kinases-1 (PAK1) signaling pathway was studied after Axl expression was downregulated by shRNA. Finally, we analyzed the expression status of Axl protein expression in hepatocellular carcinoma tissues and its relationship with the prognosis of hepatocellular carcinoma. Axl was observed to be higher expressed in MHCC97-H cell lines compared to MHCC97-L cell lines. The downregulation of Axl in MHCC97-H cell lines resulted in the inhibition of the invasion ability of MHCC97-H cells both in vitro and in vivo. Interestingly, blocking PI3K/Akt signaling pathway by LY294002 or Akt siRNA could remarkably inhibit the PAK1 activation and cell invasion. Finally, the Axl protein expression was positively correlated with differentiation, lymph node metastasis, and clinical stage in patients with hepatocellular carcinoma patients (all P < 0.01). These findings suggest that Axl can also regulate the metastasis process of hepatocellular carcinoma and may serve as a new prognostic marker and therapeutic target for treating hepatocellular carcinoma metastasis.

Li Z, Zou X, Xie L, et al.
Prognostic importance and therapeutic implications of PAK1, a drugable protein kinase, in gastroesophageal junction adenocarcinoma.
PLoS One. 2013; 8(11):e80665 [PubMed] Free Access to Full Article Related Publications
Gastroesophageal junction (GEJ) adenocarcinoma is a lethal cancer with rising incidence, yet the molecular biomarkers that have strong prognostic impact and also hold great therapeutic promise remain elusive. We used a data mining approach and identified the p21 protein-activated kinase 1 (PAK1), an oncogene and drugable protein kinase, to be among the most promising targets for GEJ adenocarcinoma. Immunoblot analysis and data mining demonstrated that PAK1 protein and mRNA were upregulated in cancer tissues compared to the noncancerous tissues. Immunohistochemistry revealed PAK1 overexpression in 72.6% of primary GEJ adenocarcinomas (n = 113). A step-wise increase in PAK1 levels was noted from paired normal epithelium, to atypical hyperplasia and adenocarcinoma. PAK1 overexpression in tumor was associated with lymph node (LN) metastasis (P<0.001), advanced tumor stage (P<0.001), large tumor size (P = 0.006), residual surgical margin (P = 0.033), and unfavorable overall survival (P<0.001). Multivariate analysis showed PAK1 overexpression is an independent high-risk prognostic predictor (P<0.001). Collectively, PAK1 is overexpressed during tumorigenic progression and its upregulation correlates with malignant properties mainly relevant to invasion and metastasis. PAK1 expression could serve as a prognostic predictor that holds therapeutic promise for GEJ adenocarcinoma.

Balbin OA, Prensner JR, Sahu A, et al.
Reconstructing targetable pathways in lung cancer by integrating diverse omics data.
Nat Commun. 2013; 4:2617 [PubMed] Free Access to Full Article Related Publications
Global 'multi-omics' profiling of cancer cells harbours the potential for characterizing the signalling networks associated with specific oncogenes. Here we profile the transcriptome, proteome and phosphoproteome in a panel of non-small cell lung cancer (NSCLC) cell lines in order to reconstruct targetable networks associated with KRAS dependency. We develop a two-step bioinformatics strategy addressing the challenge of integrating these disparate data sets. We first define an 'abundance-score' combining transcript, protein and phospho-protein abundances to nominate differentially abundant proteins and then use the Prize Collecting Steiner Tree algorithm to identify functional sub-networks. We identify three modules centred on KRAS and MET, LCK and PAK1 and β-Catenin. We validate activation of these proteins in KRAS-dependent (KRAS-Dep) cells and perform functional studies defining LCK as a critical gene for cell proliferation in KRAS-Dep but not KRAS-independent NSCLCs. These results suggest that LCK is a potential druggable target protein in KRAS-Dep lung cancers.

Licciulli S, Maksimoska J, Zhou C, et al.
FRAX597, a small molecule inhibitor of the p21-activated kinases, inhibits tumorigenesis of neurofibromatosis type 2 (NF2)-associated Schwannomas.
J Biol Chem. 2013; 288(40):29105-14 [PubMed] Free Access to Full Article Related Publications
The p21-activated kinases (PAKs) are immediate downstream effectors of the Rac/Cdc42 small G-proteins and implicated in promoting tumorigenesis in various types of cancer including breast and lung carcinomas. Recent studies have established a requirement for the PAKs in the pathogenesis of Neurofibromatosis type 2 (NF2), a dominantly inherited cancer disorder caused by mutations at the NF2 gene locus. Merlin, the protein product of the NF2 gene, has been shown to negatively regulate signaling through the PAKs and the tumor suppressive functions of Merlin are mediated, at least in part, through inhibition of the PAKs. Knockdown of PAK1 and PAK2 expression, through RNAi-based approaches, impairs the proliferation of NF2-null schwannoma cells in culture and inhibits their ability to form tumors in vivo. These data implicate the PAKs as potential therapeutic targets. High-throughput screening of a library of small molecules combined with a structure-activity relationship approach resulted in the identification of FRAX597, a small-molecule pyridopyrimidinone, as a potent inhibitor of the group I PAKs. Crystallographic characterization of the FRAX597/PAK1 complex identifies a phenyl ring that traverses the gatekeeper residue and positions the thiazole in the back cavity of the ATP binding site, a site rarely targeted by kinase inhibitors. FRAX597 inhibits the proliferation of NF2-deficient schwannoma cells in culture and displayed potent anti-tumor activity in vivo, impairing schwannoma development in an orthotopic model of NF2. These studies identify a novel class of orally available ATP-competitive Group I PAK inhibitors with significant potential for the treatment of NF2 and other cancers.

Liu KH, Huynh N, Patel O, et al.
P21-activated kinase 1 promotes colorectal cancer survival by up-regulation of hypoxia-inducible factor-1α.
Cancer Lett. 2013; 340(1):22-9 [PubMed] Related Publications
P21 activated kinase 1 (PAK1) enhances colorectal cancer (CRC) progression by stimulating Wnt/β-catenin and Ras oncogene, which promote CRC survival via stimulation of hypoxia-inducible factor 1α (HIF-1α). The aim of this study was to assess the mechanism involved in the stimulation by PAK1 of CRC survival. PAK1 promoted CRC cell survival by up-regulation of HIF-1α. PAK1 was over-expressed and hyper-activated in tumors of ApcΔ(14/+) mice, which was correlated with over-expression of HIF-1α and β-catenin. Inhibition of PAK1 decreased tumor growth and the expression of HIF-1α and β-catenin in tumors of ApcΔ(14/+) mice, and suppressed xenograft tumor survival in SCID mice. These findings indicate that PAK1 stimulates CRC survival by up-regulation of HIF-1α.

Rider L, Oladimeji P, Diakonova M
PAK1 regulates breast cancer cell invasion through secretion of matrix metalloproteinases in response to prolactin and three-dimensional collagen IV.
Mol Endocrinol. 2013; 27(7):1048-64 [PubMed] Free Access to Full Article Related Publications
p21-Activated serine-threonine kinase (PAK1) is implicated in breast cancer. We have shown previously that PAK1 is tyrosyl phosphorylated by prolactin (PRL)-activated Janus tyrosine kinase (JAK2). Although a role for both PRL and PAK1 in breast cancer is widely acknowledged, the mechanism remains poorly understood. In the present study, PRL-activated PAK1 stimulates the invasion of TMX2-28 human breast cancer cells through Matrigel. Three-dimensional (3D) collagen IV stimulates the secretion of the matrix proteases, metalloproteinase (MMP)-1 and -3 that is further enhanced by the PRL-dependent tyrosyl phosphorylation of PAK1. 3D collagen IV also stimulates the expression and secretion of MMP-2, but in contrast to MMP-1 and -3, PRL/PAK1 signaling down-regulates MMP-2 expression and secretion. In contrast, MMP-9 expression and secretion are stimulated by 3D collagen I, not collagen IV, and are not affected by PRL but are down-regulated by PAK1. MMP-1 and -3 are required and MMP-2 contributes to PRL-dependent invasion. ERK1/2 signaling appears to be required for the enhanced expression and secretion of MMP-1 and -3 and enhanced PRL-dependent invasion. p38 MAPK and c-Jun N-terminal kinase 1/2 pathways participate in production of MMP-1 and -3 as well as in PRL/PAK1-dependent cell invasion. Together, these data illustrate the complex interaction between the substratum and PRL/PAK1 signaling in human breast cancer cells and suggest a pivotal role for PRL-dependent PAK1 tyrosyl phosphorylation in MMP secretion.

Ghasemi R, Ghaffari SH, Momeny M, et al.
Multitargeting and antimetastatic potentials of silibinin in human HepG-2 and PLC/PRF/5 hepatoma cells.
Nutr Cancer. 2013; 65(4):590-9 [PubMed] Related Publications
Hepatocellular carcinoma (HCC) is the most common sort of primary liver malignancy with poor prognosis. This study aimed at examining the effects of silibinin (a putative antimetastatic agent) on some transcriptional markers mechanistically related to HCC recurrence and metastasis in HepG-2 [hepatitis B virus (HBV)-negative and P53 intact) and PLC/PRF/5 (HBV-positive and P53 mutated) cells. The expression of 27 genes in response to silibinin was evaluated by real-time RT-PCR. The MMP gelatinolytic assay and microculture tetrazolium test (MTT) were tested. Silibinin was capable of suppressing the transcriptional levels of ANGPT2, ATP6L, CAP2, CCR6, CCR7, CLDN-10, cortactin, CXCR4, GLI2, HK2, ID1, KIAA0101, mortalin, PAK1, RHOA, SPINK1, and STMN1 as well as the enzymatic activity of MMP-2 but promoted the transcripts of CREB3L3, DDX3X, and PROX1 in both cells. Some significant differences between the cells in response to silibinin were detected that might be related to the differences of the cells in terms of HBV infection and/or P53 mutation, suggesting the possible influence of silibinin on HCC through biological functions of these 2 prognostic factors. In conclusion, our findings suggest that silibinin could potentially function as a multitargeting antimetastatic agent and might provide new insights for HCC therapy particularly for HBV-related and/or P53-mutated HCCs.

Malet-Engra G, Viaud J, Ysebaert L, et al.
CIP4 controls CCL19-driven cell steering and chemotaxis in chronic lymphocytic leukemia.
Cancer Res. 2013; 73(11):3412-24 [PubMed] Related Publications
Solid tumor dissemination relies on the reprogramming of molecular pathways controlling chemotaxis. Whether the motility of nonsolid tumors such as leukemia depends on the deregulated expression of molecules decoding chemotactic signals remains an open question. We identify here the membrane remodeling F-BAR adapter protein Cdc42-interacting protein 4 (CIP4) as a key regulator of chemotaxis in chronic lymphocytic leukemia (CLL). CIP4 is expressed at abnormally high levels in CLL cells, where it is required for CCL19-induced chemotaxis. Upon CCL19 stimulation of CLL cells, CIP4 associates with GTP-bound Cdc42 and is recruited to the rear of the lamellipodium and along microspikes radiating through the lamellipodium. Consistent with its cellular distribution, CIP4 removal impairs both the assembly of the polarized lamellipodium and directional migration along a diffusible CCL19 gradient. Furthermore, CIP4 depletion results in decreased activation of WASP, but increased activation of PAK1 and p38 mitogen-activated protein kinase (MAPK). Notably, p38 MAPK inhibition results in impaired lamellipodium assembly and loss of directional migration. This suggests that CIP4 modulates both the WASP and p38 MAPK pathways to promote lamellipodium assembly and chemotaxis. Overall, our study reveals a critical role of CIP4 in mediating chemotaxis of CLL cells by controlling the dynamics of microspike-containing protrusions and cell steering.

Dart AE, Wells CM
P21-activated kinase 4--not just one of the PAK.
Eur J Cell Biol. 2013 Apr-May; 92(4-5):129-38 [PubMed] Related Publications
P21-activated kinase 4 (PAK4) is a member of the p21-activated kinase (PAK) family. Historically much of the attention has been directed towards founding family member PAK1 but the focus is now shifting towards PAK4. It is a pluripotent serine/threonine kinase traditionally recognised as a downstream effector of the Rho-family GTPases. However, emerging research over the last few years has revealed that this kinase is much more than that. New findings have shed light on the molecular mechanism of PAK4 activation and how this kinase is critical for early development. Moreover, the number of PAK4 substrates and binding partners is rapidly expanding highlighting the increasing amount of cellular functions controlled by PAK4. We propose that PAK4 should be considered a signalling integrator regulating numerous fundamental cellular processes, including actin cytoskeletal dynamics, cell morphology and motility, cell survival, embryonic development, immune defence and oncogenic transformation. This review will outline our current understanding of PAK4 biology.

Arias-Romero LE, Villamar-Cruz O, Huang M, et al.
Pak1 kinase links ErbB2 to β-catenin in transformation of breast epithelial cells.
Cancer Res. 2013; 73(12):3671-82 [PubMed] Free Access to Full Article Related Publications
p21-Activated kinase-1 (Pak1) is frequently upregulated in human breast cancer and is required for transformation of mammary epithelial cells by ErbB2. Here, we show that loss of Pak1, but not the closely related Pak2, leads to diminished expression of β-catenin and its target genes. In MMTV-ErbB2 transgenic mice, loss of Pak1 prolonged survival, and mammary tissues of such mice showed loss of β-catenin. Expression of a β-catenin mutant bearing a phospho-mimetic mutation at Ser 675, a specific Pak1 phosphorylation site, restored transformation to ErbB2-positive, Pak1-deficient mammary epithelial cells. Mice bearing xenografts of ErbB2-positive breast cancer cells showed tumor regression when treated with small-molecule inhibitors of Pak or β-catenin, and combined inhibition by both agents was synergistic. These data delineate a signaling pathway from ErbB2 to Pak to β-catenin that is required for efficient transformation of mammary epithelial cells, and suggest new therapeutic strategies in ErbB2-positive breast cancer.

Ong CC, Jubb AM, Jakubiak D, et al.
P21-activated kinase 1 (PAK1) as a therapeutic target in BRAF wild-type melanoma.
J Natl Cancer Inst. 2013; 105(9):606-7 [PubMed] Related Publications
BACKGROUND: Although remarkable clinical response rates in melanoma have been observed using vemurafenib or dabrafenib in patients with tumors carrying oncogenic mutations in BRAF, a substantial unmet medical need remains for the subset of patients with wild-type BRAF tumors.
METHODS: To investigate the role of p21-activated kinases (PAKs) in melanoma, we determined PAK1 genomic copy number and protein expression for a panel of human melanoma tissues. PAK1 was inhibited in vitro and in vivo using RNA interference or PF-3758309 inhibitor treatment in a panel of melanoma cell lines with known BRAF and RAS (rat sarcoma) genotype to better understand its role in melanoma cell proliferation and migration. Tumorigenesis was assessed in vivo in female NCR nude mice and analyzed with cubic spline regression and area under the curve analyses. All statistical tests were two-sided.
RESULTS: Strong cytoplasmic PAK1 protein expression was prevalent in melanomas (27%) and negatively associated with activating mutation of the BRAF oncogene (P < .001). Focal copy number gain of PAK1 at 11q13 was also observed in 9% of melanomas (n = 87; copy number ≥ 2.5) and was mutually exclusive with BRAF mutation (P < .005). Selective PAK1 inhibition attenuated signaling through mitogen-activated protein kinase (MAPK) as well as cytoskeleton-regulating pathways to modulate the proliferation and migration of BRAF wild-type melanoma cells. Treatment of BRAF wild-type melanomas with PF-3758309 PAK inhibitor decreased tumor growth for SK-MEL23 and 537MEL xenografts (91% and 63% inhibition, respectively; P < .001) and MAPK pathway activation in vivo.
CONCLUSIONS: Taken together, our results provide evidence for a functional role of PAK1 in BRAF wild-type melanoma and therapeutic use of PAK inhibitors in this indication.

Chen L, Liu H, Liu J, et al.
Klotho endows hepatoma cells with resistance to anoikis via VEGFR2/PAK1 activation in hepatocellular carcinoma.
PLoS One. 2013; 8(3):e58413 [PubMed] Free Access to Full Article Related Publications
Klotho was originally characterized as an aging suppressor gene that predisposed Klotho-deficient mice to premature aging-like syndrome. Although Klotho was recently reported to exhibit tumor suppressive properties during various malignant transformations, the functional role and molecular mechanism of Klotho in hepatocarcinogenesis remains poorly understood. In our present study, immunohistochemical Klotho staining levels in a clinical follow-up of 52 hepatoma patients were significantly associated with liver cirrhosis, tumor multiplicity and venous invasion. The overall survival rate of hepatoma patients with high Klotho expression was significantly lower than those patients with low Klotho expression. Moreover, Klotho overexpression increased cellular migration, anchorage-independent growth, and anoikis resistance in hepatoma cells. Klotho overexpression elevated p21-activated kinase 1 (PAK1) expression and shRNA-mediated PAK1 knockdown and kinase activity inhibition with kinase dead mutant PAK1 K299R coexpression or allosteric inhibitor IPA3 treatment reversed anoikis resistance in Klotho-overexpressed hepatoma cells. More importantly, the pivotal significance of upregulated VEGFR2 protein levels mediated by Klotho expression was confirmed by VEGFR2 inhibitor Axitinib and blocking antibody treatment in hepatoma cells. Axitinib treatment sensitized anoikis was reversed by constitutive active mutant PAK1 T423E coexpression in Klotho-overexpressed hepatoma cells. Conversely, knockdown of Klotho reduced VEGFR2/PAK1 dependent anoikis resistance, which could be reversed by PAK1 T423E. These results revealed a novel oncogenic function of Klotho in promoting anoikis resistance via activating VEGFR2/PAK1 signaling, thus facilitating tumor migration and invasion during hepatoma progression, which could provide a putative molecular mechanism for tumor metastasis.

Hu X, Guo J, Zheng L, et al.
The heterochronic microRNA let-7 inhibits cell motility by regulating the genes in the actin cytoskeleton pathway in breast cancer.
Mol Cancer Res. 2013; 11(3):240-50 [PubMed] Free Access to Full Article Related Publications
The heterochronic gene let-7 serves as a tumor suppressor microRNA by targeting various oncogenic pathways in cancer cells. Considerable evidence indicates that reduced expression of let-7 might be associated with poor clinical outcome in patients with cancer. Here, we report that the expression levels of three let-7 family members, let-7a, let-7b, and let-7g, were significantly decreased in the patients with breast cancer with lymph node metastasis compared with those without lymph node metastasis. Enforced expression of let-7b significantly inhibits breast cancer cell motility and affects actin dynamics. Using bioinformatic and experimental approaches, four genes in the actin cytoskeleton pathway, including PAK1, DIAPH2, RDX, and ITGB8, were identified as let-7 direct targets. Blocking the expression of PAK1, DIAPH2, and RDX significantly inhibits breast cancer cell migration induced by let-7b repression. Our results indicate that reconstitution of let-7 expression in tumor cells could provide a novel therapeutic strategy for the treatment of metastatic disease.

Lu W, Qu JJ, Li BL, et al.
Overexpression of p21-activated kinase 1 promotes endometrial cancer progression.
Oncol Rep. 2013; 29(4):1547-55 [PubMed] Related Publications
Endometrial cancer (EC) is the most common gynecologic malignancy, but the molecular events involved in the development and progression of EC remain unclear. P21-activated kinase 1 (Pak1) plays important roles in cell motility and survival. This study investigated the clinical significance of Pak1 expression and its functional roles in EC. The expression of Pak1 in clinical samples and EC cell lines was evaluated. The effects of Pak1 on EC cell functions were determined by either overexpressing it via plasmid transfection or depleting its expression using short hairpin RNA (shRNA) in human EC cell lines. Pak1 was overexpressed in clinical samples of EC compared with normal endometrium. High Pak1 expression in EC was positively correlated with lymph node metastasis, advanced disease stage and poor histological differentiation. Pak1 over-expression was also observed in multiple human EC cell lines. In EC cell lines, Pak1 overexpression promoted cell proliferation, migration, invasion and anchorage-independent growth in vitro. Conversely, shRNA-mediated stable knockdown of Pak1 reduced cell proliferation, migration, invasion and anchorage-independent growth. In addition, ectopic Pak1 overexpression protected EC cells from apoptosis, along with decreased caspase-3 activation. These results suggest that Pak1 plays important roles at multiple stages of EC progression.

Sun D, Yu F, Ma Y, et al.
MicroRNA-31 activates the RAS pathway and functions as an oncogenic MicroRNA in human colorectal cancer by repressing RAS p21 GTPase activating protein 1 (RASA1).
J Biol Chem. 2013; 288(13):9508-18 [PubMed] Free Access to Full Article Related Publications
MicroRNAs (miRNAs) are known to play a vital role in colorectal cancer. We found a widespread disruption in miRNA expression during colorectal tumorigenesis using microarray and quantitative RT-PCR analysis; of the 161 miRNAs altered in colorectal cancer compared with normal adjacent tissue samples, miR-31 was the most significantly dysregulated. We identified candidate targets of miR-31 using bioinformatics approaches and validated RAS p21 GTPase activating protein 1 (RASA1) as a direct target. First, we found an inverse correlation between miR-31 and RASA1 protein levels in vivo. Second, in vitro evidence demonstrated that RASA1 expression was significantly decreased by treatment with pre-miR-31-LV, whereas anti-miR-31-LV treatment increased RASA1 protein levels. Third, a luciferase reporter assay confirmed that miR-31 directly recognizes a specific location within the 3'-untranslated region of RASA1 transcripts. Furthermore, the biological consequences of miR-31 targeting RASA1 were examined by the cell proliferation assay in vitro and by the immunodeficient mouse xenograft tumor model in vivo. Taken together, our results demonstrate for the first time that miR-31 plays a significant role in activating the RAS signaling pathway through the inhibition of RASA1 translation, thereby improving colorectal cancer cell growth and stimulating tumorigenesis.

Lee JH, Wittki S, Bräu T, et al.
HIV Nef, paxillin, and Pak1/2 regulate activation and secretion of TACE/ADAM10 proteases.
Mol Cell. 2013; 49(4):668-79 [PubMed] Related Publications
The HIV Nef protein recruits the polycomb protein Eed and mimics an integrin receptor signal for reasons that are not entirely clear. Here we demonstrate that Nef and Eed complex with the integrin effector paxillin to recruit and activate TNFα converting enzyme (TACE alias ADAM 17) and its close relative ADAM10. The activated proteases cleaved proTNFα and were shuttled into extracellular vesicles (EVs). Peripheral blood mononuclear cells that ingested these EVs released TNFα. Analyzing the mechanism, we found that Pak2, an established host cell effector of Nef, phosphorylated paxillin on Ser272/274 to induce TACE-paxillin association and shuttling into EVs via lipid rafts. Conversely, Pak1 phosphorylated paxillin on Ser258, which inhibited TACE association and lipid raft transfer. Interestingly, melanoma cells used an identical mechanism to shuttle predominantly ADAM10 into EVs. We conclude that HIV-1 and cancer cells exploit a paxillin/integrin-controlled mechanism to release TACE/ADAM10-containing vesicles, ensuring better proliferation/growth conditions in their microenvironment.

Walsh K, McKinney MS, Love C, et al.
PAK1 mediates resistance to PI3K inhibition in lymphomas.
Clin Cancer Res. 2013; 19(5):1106-15 [PubMed] Free Access to Full Article Related Publications
PURPOSE: The phosphoinositide 3-kinase (PI3K) pathway is known to play an active role in many malignancies. The role of PI3K inhibition in the treatment of lymphomas has not been fully delineated. We sought to identify a role for therapeutic PI3K inhibition across a range of B-cell lymphomas.
EXPERIMENTAL DESIGN: We selected three small molecule inhibitors to test in a panel of 60 cell lines that comprised diverse lymphoma types. We tested the selective PI3K inhibitor BKM120 and the dual PI3K/mTOR inhibitors BEZ235 and BGT226 in these cell lines. We applied gene expression profiling to better understand the molecular mechanisms associated with responsiveness to these drugs.
RESULTS: We found that higher expression of the PAK1 gene was significantly associated with resistance to all three PI3K inhibitors. Through RNA-interference-mediated knockdown of the PAK1 gene, we showed a dramatic increase in the sensitivity to PI3K inhibition. We further tested a small-molecule inhibitor of PAK1 and found significant synergy between PI3K and PAK1 inhibition.
CONCLUSION: Thus, we show that PI3K inhibition is broadly effective in lymphomas and PAK1 is a key modulator of resistance to PI3K inhibition.

Goc A, Al-Azayzih A, Abdalla M, et al.
P21 activated kinase-1 (Pak1) promotes prostate tumor growth and microinvasion via inhibition of transforming growth factor β expression and enhanced matrix metalloproteinase 9 secretion.
J Biol Chem. 2013; 288(5):3025-35 [PubMed] Free Access to Full Article Related Publications
P21-activated kinases (Paks) are major effectors downstream of the small Rho family of GTPases. Among the six isoforms, Pak1 is the most ubiquitous and the best characterized member. Previous studies have shown that inhibition of Pak6, which is predominantly present in the prostate compared with other tissues, inhibits prostate tumor growth in vivo. Even though Pak1 has been identified in normal prostatic epithelial cells and cancer cells, its specific role in the development of prostate cancer remains unclear. We report here that highly invasive prostate cancer cells express significantly higher levels of Pak1 protein compared with non-invasive prostate cancer cells. Furthermore, prostate tumor tissues and prostate cancer metastasized to lungs showed a higher expression of Pak1 compared with normal tissues. Interestingly, Pak6 protein expression levels did not change with the invasive/metastatic potential of the cancer cells or tumors. Although inhibition of Pak1, and not Pak6, resulted in impaired PC3 cell migration, the effects of Pak1 knockdown on transendothelial migration (microinvasion), tumor growth, and tumor angiogenesis was higher compared with Pak6 knockdown. Finally, gene array data revealed reduced expression of matrix metalloproteinase 9 with the ablation of either Pak1 or Pak6 gene expression in PC3 cells, whereas protein levels of TGFβ was elevated significantly with specific modulation of Pak1 activity or ablation of the Pak1 gene. Our observations suggest that although some level of functional redundancy exists between Pak1 and Pak6 in prostate cancer cells, targeting Pak1 is a potential option for the management of prostate tumor growth, microinvasion, and metastasis.

Tabusa H, Brooks T, Massey AJ
Knockdown of PAK4 or PAK1 inhibits the proliferation of mutant KRAS colon cancer cells independently of RAF/MEK/ERK and PI3K/AKT signaling.
Mol Cancer Res. 2013; 11(2):109-21 [PubMed] Related Publications
The p21-activated kinase (PAK) serine/threonine kinases are important effectors of the small GTPases Rac and Cdc42, and play significant roles in controlling cell growth, motility, and transformation. Knockdown of PAK4 or PAK1 inhibited the proliferation of mutant KRAS or BRAF colon cancer cells in vitro. Dependence on PAK4 or PAK1 protein for colon cancer cell proliferation was independent of PAK4 or PAK1 protein expression levels. Mutant KRAS HCT116 colorectal cells were the most sensitive to PAK4 or PAK1 knockdown resulting in the potent inhibition of anchorage-dependent and -independent proliferation as well as the formation and proliferation of HCT116 colon cancer spheroids. This inhibition of proliferation did not correlate with inhibition of RAF/MEK/ERK or PI3K/AKT signaling. In HCT116 cells, knockdown of PAK4 or PAK1 caused changes to the actin cytoskeleton resulting in reduced basal spread and cell elongation and increased cell rounding. These cytoskeletal rearrangements seemed to be independent of LIMK/cofilin/paxillin phosphorylation. PAK4 or PAK1 knockdown initially induced growth arrest in HCT116 cells followed by cell death at later time points. Inhibition of the antiapoptotic proteins Bcl-2 and Bcl-X(L) with the pharmacologic inhibitor ABT-737 increased effector caspase activation and apoptosis, and reduced cell survival with PAK4 or PAK1 knockdown. These results support a role for the PAKs in the proliferation of mutant KRAS-driven colorectal carcinoma cells via pathways not involving RAF/MEK/ERK and PI3K/AKT signaling.

Zhou Y, Su J, Shi L, et al.
DADS downregulates the Rac1-ROCK1/PAK1-LIMK1-ADF/cofilin signaling pathway, inhibiting cell migration and invasion.
Oncol Rep. 2013; 29(2):605-12 [PubMed] Related Publications
The aim of this study was to explore the molecular mechanisms of the diallyl disulfide (DADS)-mediated downregulation of LIM kinase-1 (LIMK1) and the consequent inhibition of the migration and invasion of human colorectal cancer cells. RNA interference technology was used to establish stable LIMK1-miRNA/SW480 cell lines. The effects of DADS and LIMK1 RNA interference on the migration and invasion of SW480 cells were observed by scratch wound healing assay and Transwell migration assay. The effects of DADS on signaling molecules of the Rac1-Rho kinase (ROCK)1/p21-activated kinase (PAK)1-LIM kinase (LIMK)1-actin depolymerizing factor (ADF)/cofilin pathway in SW480 cells were examined by RT-PCR and western blot analysis. The healing and migration rate of the SW480 cells was significantly reduced and the cell penetrating ability was significantly suppressed (P<0.05) following treatment with DADS (45 mg/l). The immunohistochemistry and western blot analysis results showed that DADS significantly downregulated LIMK1 protein expression and suppressed LIMK1 protein phosphorylation. Furthermore, the RT-PCR and western blot analysis results revealed that DADS suppressed Rac1, ROCK1, PAK1, LIMK1 and destrin mRNA and protein expression, as well as the protein phosphorylation of LIMK1 and cofilin 1. The data demonstrate that LIMK1 expression positively correlates with the SW480 cell migration and invasion ability. DADS downregulates the Rac1-ROCK1/PAK1-LIMK1-ADF/cofilin signaling pathway, suppressing SW480 cell migration and invasion.

Khare V, Lyakhovich A, Dammann K, et al.
Mesalamine modulates intercellular adhesion through inhibition of p-21 activated kinase-1.
Biochem Pharmacol. 2013; 85(2):234-44 [PubMed] Free Access to Full Article Related Publications
Mesalamine (5-ASA) is widely used for the treatment of ulcerative colitis, a remitting condition characterized by chronic inflammation of the colon. Knowledge about the molecular and cellular targets of 5-ASA is limited and a clear understanding of its activity in intestinal homeostasis and interference with neoplastic progression is lacking. We sought to identify molecular pathways interfered by 5-ASA, using CRC cell lines with different genetic background. Microarray was performed for gene expression profile of 5-ASA-treated and untreated cells (HCT116 and HT29). Filtering and analysis of data identified three oncogenic pathways interfered by 5-ASA: MAPK/ERK pathway, cell adhesion and β-catenin/Wnt signaling. PAK1 emerged as a consensus target of 5-ASA, orchestrating these pathways. We further investigated the effect of 5-ASA on cell adhesion. 5-ASA increased cell adhesion which was measured by cell adhesion assay and transcellular-resistance measurement. Moreover, 5-ASA treatment restored membranous expression of adhesion molecules E-cadherin and β-catenin. Role of PAK1 as a mediator of mesalamine activity was validated in vitro and in vivo. Inhibition of PAK1 by RNA interference also increased cell adhesion. PAK1 expression was elevated in APC(min) polyps and 5-ASA treatment reduced its expression. Our data demonstrates novel pharmacological mechanism of mesalamine in modulation of cell adhesion and role of PAK1 in APC(min) polyposis. We propose that inhibition of PAK1 expression by 5-ASA can impede with neoplastic progression in colorectal carcinogenesis. The mechanism of PAK1 inhibition and induction of membranous translocation of adhesion proteins by 5-ASA might be independent of its known anti-inflammatory action.

Habif G, Grasset MF, Kieffer-Jaquinod S, et al.
Phosphoproteome analyses reveal specific implications of Hcls1, p21-activated kinase 1 and Ezrin in proliferation of a myeloid progenitor cell line downstream of wild-type and ITD mutant Fms-like tyrosine kinase 3 receptors.
J Proteomics. 2013; 78:231-44 [PubMed] Related Publications
The tyrosine kinase receptor Flt3 (Fms-like tyrosine kinase 3) is almost always expressed in AML (acute myeloid leukemia) cells, and constitutive activation of Flt3 by ITD (internal tandem duplication) mutations is one of the most common molecular alterations known in AML, especially monocytic AML. Furthermore, Flt3-ligand (FL) was shown as an in vitro growth factor for monocytic precursors, pointing to the important role of Flt3 in the regulation of monocyte/macrophage production. To get a relevant model for studying the molecular mechanisms underlying the physiopathological role of Flt3 on monocytic lineage development, we used the IL-3 dependent murine myeloid progenitors FDC-P1 cell line to generate cells stably co-expressing murine Fms (M-CSF receptor) and human Flt3. Wild type (WT)-Flt3 expressing cells could proliferate in an FL-dependent manner, whereas those expressing Flt3-ITD all survived IL-3 deprivation and showed autonomous proliferation, whereas both types of cells could differentiate to monocytic cells in response to M-CSF. Next, by combining phosphoprotein detection or purification, comparative 2D-PAGE and mass spectrometry sequencing, we sought for downstream mediators of Flt3-WT or Flt3-ITD in FD/Fms cell proliferation. Amongst the differentially expressed and/or phosphorylated proteins, 3 showed a specific implication in FD/Fms cell proliferation: Hcls1 and the Pak1/2 in FL-dependent proliferation of Flt3-WT expressing cells and Ezrin in autonomous proliferation of Flt3-ITD expressing cells.

Chow HY, Jubb AM, Koch JN, et al.
p21-Activated kinase 1 is required for efficient tumor formation and progression in a Ras-mediated skin cancer model.
Cancer Res. 2012; 72(22):5966-75 [PubMed] Free Access to Full Article Related Publications
The RAS genes are the most commonly mutated oncogenes in human cancer and present a particular therapeutic dilemma, as direct targeting of Ras proteins by small molecules has proved difficult. Signaling pathways downstream of Ras, in particular Raf/Mek/Erk and PI3K/Akt/mTOR, are dominated by lipid and protein kinases that provide attractive alternate targets in Ras-driven tumors. As p21-activated kinase 1 (Pak1) has been shown to regulate both these signaling pathways and is itself upregulated in many human cancers, we assessed the role of Pak1 in Ras-driven skin cancer. In human squamous cell carcinoma (SCC), we found a strong positive correlation between advanced stage and grade and PAK1 expression. Using a mouse model of Kras-driven SCC, we showed that deletion of the mouse Pak1 gene led to markedly decreased tumorigenesis and progression, accompanied by near total loss of Erk and Akt activity. Treatment of Kras(G12D) mice with either of two distinct small molecule Pak inhibitors (PF3758309 and FRAX597) caused tumor regression and loss of Erk and Akt activity. Tumor regression was also seen in mice treated with a specific Mek inhibitor, but not with an Akt inhibitor. These findings establish Pak1 as a new target in KRAS-driven tumors and suggest a mechanism of action through the Erk, but not the Akt, signaling pathway.

Ho H, Aruri J, Kapadia R, et al.
RhoJ regulates melanoma chemoresistance by suppressing pathways that sense DNA damage.
Cancer Res. 2012; 72(21):5516-28 [PubMed] Free Access to Full Article Related Publications
Melanomas resist conventional chemotherapeutics, in part, through intrinsic disrespect of apoptotic checkpoint activation. In this study, using an unbiased genome-wide RNA interference screen, we identified RhoJ and its effector PAK1, as key modulators of melanoma cell sensitivity to DNA damage. We find that RhoJ activates PAK1 in response to drug-induced DNA damage, which then uncouples ATR from its downstream effectors, ultimately resulting in a blunted DNA damage response (DDR). In addition, ATR suppression leads to the decreased phosphorylation of ATF2 and consequent increased expression of the melanocyte survival gene Sox10 resulting in a higher DDR threshold required to engage melanoma cell death. In the setting of normal melanocyte behavior, this regulatory relationship may facilitate appropriate epidermal melanization in response to UV-induced DNA damage. However, pathologic pathway activation during oncogenic transformation produces a tumor that is intrinsically resistant to chemotherapy and has the propensity to accumulate additional mutations. These findings identify DNA damage agents and pharmacologic inhibitors of RhoJ/PAK1 as novel synergistic agents that can be used to treat melanomas that are resistant to conventional chemotherapies.

Kawahara M, Pandolfi A, Bartholdy B, et al.
H2.0-like homeobox regulates early hematopoiesis and promotes acute myeloid leukemia.
Cancer Cell. 2012; 22(2):194-208 [PubMed] Free Access to Full Article Related Publications
Homeobox domain-containing transcription factors are important regulators of hematopoiesis. Here, we report that increased levels of nonclustered H2.0-like homeobox (HLX) lead to loss of functional hematopoietic stem cells and formation of aberrant progenitors with unlimited serial clonogenicity and blocked differentiation. Inhibition of HLX reduces proliferation and clonogenicity of leukemia cells, overcomes the differentiation block, and leads to prolonged survival. HLX regulates a transcriptional program, including PAK1 and BTG1, that controls cellular differentiation and proliferation. HLX is overexpressed in 87% of patients with acute myeloid leukemia (AML) and independently correlates with inferior overall survival (n = 601, p = 2.3 × 10(-6)). Our study identifies HLX as a key regulator in immature hematopoietic and leukemia cells and as a prognostic marker and therapeutic target in AML.

Singhal R, Kandel ES
The response to PAK1 inhibitor IPA3 distinguishes between cancer cells with mutations in BRAF and Ras oncogenes.
Oncotarget. 2012; 3(7):700-8 [PubMed] Free Access to Full Article Related Publications
While new drugs aimed at BRAF-mutated cancers are entering clinical practice, cells and tumors with activating Ras mutations are relatively resistant to those and quite a few other anti-cancer agents. This inspires the effort to reverse this resistance or to uncover new vulnerabilities in such resistant cancers. IPA3 has been originally identified as a small molecule inhibitor of p21-activated protein kinase 1 (PAK1), a candidate therapeutic target in human malignancies. We have tested a battery of melanoma and colon carcinoma cell lines that carry mutations in BRAF, NRAS and KRAS genes and have observed that those with NRAS and KRAS mutations are more sensitive to killing by IPA3. Genetic manipulations suggest that the differential response depends not just on these oncogenes, but also on additional events that were co-selected during tumor evolution. Furthermore, sublethal doses of IPA3 or ectopic expression of dominant-negative PAK1 sensitized Ras-mutated cells to GDC-0897 and AZD6244, which otherwise have reduced efficiency against cells with activated Ras. Dominant-negative PAK1 also reduced the growth of NRAS-mutated cells in confluent cultures, but, unlike IPA3, caused no significant toxicity. Although it remains to be proven that all the effects of IPA3 are exclusively due to inhibition of PAK1, our findings point to the existence of selective vulnerabilities, which are associated with Ras mutations and could be useful for better understanding and treatment of a large subset of tumors.

Rettig M, Trinidad K, Pezeshkpour G, et al.
PAK1 kinase promotes cell motility and invasiveness through CRK-II serine phosphorylation in non-small cell lung cancer cells.
PLoS One. 2012; 7(7):e42012 [PubMed] Free Access to Full Article Related Publications
The role of c-Crk (CRK) in promoting metastasis is well described however the role of CRK phosphorylation and the corresponding signaling events are not well explained. We have observed CRK-II serine 41 phosphorylation is inversely correlated with p120-catenin and E-cadherin expressions in non-small cell lung cancer (NSCLC) cells. Therefore, we investigated the role of CRK-II serine 41 phosphorylation in the down-regulation of p120-catenin, cell motility and cell invasiveness in NSCLC cells. For this purpose, we expressed phosphomimetic and phosphodeficient CRK-II serine 41 mutants in NSCLC cells. NSCLC cells expressing phosphomimetic CRK-II seine 41 mutant showed lower p120-catenin level while CRK-II seine 41 phosphodeficient mutant expression resulted in higher p120-catenin. In addition, A549 cells expressing CRK-II serine 41 phosphomimetic mutant demonstrated more aggressive behavior in wound healing and invasion assays and, on the contrary, expression of phosphodeficient CRK-II serine 41 mutant in A549 cells resulted in reduced cell motility and invasiveness. We also provide evidence that PAK1 mediates CRK-II serine 41 phosphorylation. RNAi mediated silencing of PAK1 increased p120-catenin level in A549 and H157 cells. Furthermore, PAK1 silencing decreased cell motility and invasiveness in A549 cells. These effects were abrogated in A549 cells expressing phosphomimetic CRK-II serine 41. In summary, these data provide evidence for the role of PAK1 in the promotion of cell motility, cell invasiveness and the down regulation of p120-catenin through CRK serine 41 phosphorylation in NSCLC cells.

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