Gene Summary

Gene:SKIL; SKI-like proto-oncogene
Aliases: SNO, SnoA, SnoI, SnoN
Summary:The protein encoded by this gene is a component of the SMAD pathway, which regulates cell growth and differentiation through transforming growth factor-beta (TGFB). In the absence of ligand, the encoded protein binds to the promoter region of TGFB-responsive genes and recruits a nuclear repressor complex. TGFB signaling causes SMAD3 to enter the nucleus and degrade this protein, allowing these genes to be activated. Four transcript variants encoding three different isoforms have been found for this gene. [provided by RefSeq, Oct 2011]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:ski-like protein
Source:NCBIAccessed: 25 June, 2015


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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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.

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: SKIL (cancer-related)

Moir-Meyer GL, Pearson JF, Lose F, et al.
Rare germline copy number deletions of likely functional importance are implicated in endometrial cancer predisposition.
Hum Genet. 2015; 134(3):269-78 [PubMed] Related Publications
Endometrial cancer is the most common invasive gynaecological cancer in women, and relatively little is known about inherited risk factors for this disease. This is the first genome-wide study to explore the role of common and rare germline copy number variants (CNVs) in predisposition to endometrial cancer. CNVs were called from germline DNA of 1,209 endometrioid endometrial cancer cases and 528 cancer-unaffected female controls. Overall CNV load of deletions or DNA gains did not differ significantly between cases and controls (P > 0.05), but cases presented with an excess of rare germline deletions overlapping likely functional genomic regions including genes (P = 8 × 10(-10)), CpG islands (P = 1 × 10(-7)) and sno/miRNAs regions (P = 3 × 10(-9)). On average, at least one additional gene and two additional CpG islands were disrupted by rare deletions in cases compared to controls. The most pronounced difference was that over 30 sno/miRNAs were disrupted by rare deletions in cases for every single disruption event in controls. A total of 13 DNA repair genes were disrupted by rare deletions in 19/1,209 cases (1.6%) compared to one gene in 1/528 controls (0.2%; P = 0.007), and this increased DNA repair gene loss in cases persisted after excluding five individuals carrying CNVs disrupting mismatch repair genes MLH1, MSH2 and MSH6 (P = 0.03). There were 34 miRNA regions deleted in at least one case but not in controls, the most frequent of which encompassed hsa-mir-661 and hsa-mir-203. Our study implicates rare germline deletions of functional and regulatory regions as possible mechanisms conferring endometrial cancer risk, and has identified specific regulatory elements as candidates for further investigation.

Park MA, Choi KC
Effects of 4-nonylphenol and bisphenol A on stimulation of cell growth via disruption of the transforming growth factor-β signaling pathway in ovarian cancer models.
Chem Res Toxicol. 2014; 27(1):119-28 [PubMed] Related Publications
Transforming growth factor β (TGF-β) signaling pathway is a major pathway in cellular processes such as cell growth, apoptosis, and cellular homeostasis. The signaling pathway activated by 17β-estadiol (E2) appeared to inhibit the TGF-β signaling pathway by cross-talk with the TGF-β components in estrogen receptor (ER) positive cells. In this study, we examined the inhibitory effects of endocrine disrupting chemicals (EDCs), including 4-nonylphenol (NP), 4-otylphenol (OP), bisphenol A (BPA), and benzophenon-1 (BP-1), in the TGF-β signaling pathway in BG-1 ovarian cancer cells expressing estrogen receptors (ERs). The transcriptional and translational levels of TGF-β related genes were examined by reverse transcription-PCR (RT-PCR), Western blot analysis, and xenograft mouse models of ovarian cancer cells. As a result, treatment with NP, OP, and BPA induced the expressions of SnoN, a TGF-β pathway inhibitor, and c-Fos, a TGF-β target transcription factor. Treatment with NP, BPA, and BP-1 resulted in decreased phosphorylation of Smad3, a downstream target of TGF-β. These results indicate that NP and BPA may stimulate the proliferation of BG-1 cells via inhibition of the TGF-β signaling pathway. In a xenograft mouse model, transplanted BG-1 ovarian cancer cells showed significantly decreased phosphorylation of Smad3 and increased expression of SnoN in the ovarian tumor masses following treatment with E2, NP, or BPA. In parallel with an in vitro model, the expressions of these TGF-β signaling pathway were similarly regulated by NP or BPA in a xenograft mouse model. These results support the fact that the existence of an unproven relationship between EDCs/ER-α and TGF-β signaling pathway and a further study are required in order to verify more profound and distinct mechanism(s) for the disturbance of the TGF-β signaling pathway by diverse EDCs.

Ronchetti D, Mosca L, Cutrona G, et al.
Small nucleolar RNAs as new biomarkers in chronic lymphocytic leukemia.
BMC Med Genomics. 2013; 6:27 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Small nucleolar RNAs (snoRNAs) and small Cajal body-specific RNAs are non-coding RNAs involved in the maturation of other RNA molecules. Alterations of sno/scaRNA expression may play a role in cancerogenesis. This study elucidates the patterns of sno/scaRNA expression in 211 chronic lymphocytic leukemia (CLL) patients (Binet stage A) also in comparison with those of different normal B-cell subsets.
METHODS: The patterns of sno/scaRNA expression in highly purified CD19+ B-cells of 211 CLL patients and in 18 normal B-cell samples--6 from peripheral blood, and 12 from tonsils (4 germinal center, 2 marginal zone, 3 switched memory and 3 naïve B-cells)--were analyzed on the Affymetrix GeneChip® Human Gene 1.0 ST array.
RESULTS: CLLs display a sno/scaRNAs expression profile similar to normal memory, naïve and marginal-zone B-cells, with the exception of a few down-regulated transcripts (SNORA31, -6, -62, and -71C). Our analyses also suggest some heterogeneity in the pattern of sno/scaRNAs expression which is apparently unrelated to the major biological (ZAP-70 and CD38), molecular (IGHV mutation) and cytogenetic markers. Moreover, we found that SNORA70F was significantly down-regulated in poor prognostic subgroups and this phenomenon was associated with the down-regulation of its host gene COBLL1. Finally, we generated an independent model based on SNORA74A and SNORD116-18 expression, which appears to distinguish two different prognostic CLL groups.
CONCLUSIONS: These data extend the view of sno/scaRNAs deregulation in cancer and may contribute to discover novel biomarkers associated with the disease and potentially useful to predict the clinical outcome of early stage CLL patients.

Hagerstrand D, Tong A, Schumacher SE, et al.
Systematic interrogation of 3q26 identifies TLOC1 and SKIL as cancer drivers.
Cancer Discov. 2013; 3(9):1044-57 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: 3q26 is frequently amplified in several cancer types with a common amplified region containing 20 genes. To identify cancer driver genes in this region, we interrogated the function of each of these genes by loss- and gain-of-function genetic screens. Specifically, we found that TLOC1 (SEC62) was selectively required for the proliferation of cell lines with 3q26 amplification. Increased TLOC1 expression induced anchorage-independent growth, and a second 3q26 gene, SKIL (SNON), facilitated cell invasion in immortalized human mammary epithelial cells. Expression of both TLOC1 and SKIL induced subcutaneous tumor growth. Proteomic studies showed that TLOC1 binds to DDX3X, which is essential for TLOC1-induced transformation and affected protein translation. SKIL induced invasion through upregulation of SLUG (SNAI2) expression. Together, these studies identify TLOC1 and SKIL as driver genes at 3q26 and more broadly suggest that cooperating genes may be coamplified in other regions with somatic copy number gain.
SIGNIFICANCE: These studies identify TLOC1 and SKIL as driver genes in 3q26. These observations provide evidence that regions of somatic copy number gain may harbor cooperating genes of different but complementary functions.

Kodigepalli KM, Anur P, Spellman P, et al.
Phospholipid Scramblase 1, an interferon-regulated gene located at 3q23, is regulated by SnoN/SkiL in ovarian cancer cells.
Mol Cancer. 2013; 12:32 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Treatment of advanced stage ovarian cancer continues to be challenging due to acquired drug resistance and lack of early stage biomarkers. Genes identified to be aberrantly expressed at the 3q26.2 locus (i.e. SnoN/SkiL) have been implicated in ovarian cancer pathophysiology. We have previously shown that SnoN expression is increased in advanced stage ovarian cancers and alters cellular response to arsenic trioxide (As2O3).
FINDINGS: We now demonstrate increased DNA copy number levels (TCGA data) of phospholipid scramblase 1 (PLSCR1, located at 3q23) whose transcript expression in ovarian cell lines is highly correlated with SnoN mRNA. Interestingly, SnoN can modulate PLSCR1 mRNA levels in the absence/presence of interferon (IFN-2α). Both IFN-2α and As2O3 treatment can modulate PLSCR1 mRNA levels in ovarian carcinoma cells. However, SnoN siRNA does not lead to altered PLSCR1 protein implicating other events needed to modulate its protein levels. In addition, we report that PLSCR1 can modulate aspects of the As2O3 cellular response.
CONCLUSIONS: Our findings warrant further investigation into the role of PLSCR1 in ovarian cancer development and chemoresistance.

Nallar SC, Kalvakolanu DV
Regulation of snoRNAs in cancer: close encounters with interferon.
J Interferon Cytokine Res. 2013; 33(4):189-98 [PubMed] Free Access to Full Article Related Publications
The interferon (IFN) family of cytokines regulates many cellular processes, such as transcription, translation, post-translational modifications, and protein degradation. IFNs induce growth inhibition and/or cell death, depending on the cell type, by employing different proteins. This review describes a novel growth-suppressive pathway employed by IFNs that affects rRNA levels. Maturation of rRNA involves numerous noncoding small regulatory RNA-guided processes. These regulatory RNAs, called small nucleolar RNA (snoRNAs), function as a ribonucleoprotein particle (RNP) in the nucleolus. The biogenesis of snoRNPs is dependent on core protein and assembly factors. Our laboratory recently isolated a growth-suppressive protein gene associated with retinoid-IFN-induced mortality (GRIM)-1 using a genetic screen. IFN-inducible GRIM-1 (SHQ1) is an assembly factor that controls one arm of the snoRNP machinery. GRIM-1 inhibits sno/scaRNP formation to induce growth suppression via reduction in mature rRNA levels. Loss of GRIM-1 observed in certain cancers implicates it to be a novel tumor suppressor. Certain snoRNAs have been reported to act as either oncogenes or tumor suppressors in vitro. Recent studies have shown that certain sno/scaRNAs are further processed into micro RNA-like molecules to control translation of protein-coding RNAs. We present a model as to how these small regulatory RNAs influence cell growth and a potential role for GRIM-1 in this process.

Briones-Orta MA, Levy L, Madsen CD, et al.
Arkadia regulates tumor metastasis by modulation of the TGF-β pathway.
Cancer Res. 2013; 73(6):1800-10 [PubMed] Free Access to Full Article Related Publications
TGF-β can act as a tumor suppressor at early stages of cancer progression and as a tumor promoter at later stages. The E3 ubiquitin ligase Arkadia (RNF111) is a critical component of the TGF-β signaling pathway, being required for a subset of responses, those mediated by Smad3-Smad4 complexes. It acts by mediating ligand-induced degradation of Ski and SnoN (SKIL), which are 2 potent transcriptional repressors. Here, we investigate the role of Arkadia in cancer using model systems to address both potential tumor-suppressive and tumor-promoting roles. Stable reexpression of Arkadia in lung carcinoma NCI-H460 cells, which we show contain a hemizygous nonsense mutation in the Arkadia/RNF111 gene, efficiently restored TGF-β-induced Smad3-dependent transcription, and substantially decreased the ability of these cells to grow in soft agar in vitro. However, it had no effect on tumor growth in vivo in mouse models. Moreover, loss of Arkadia in cancer cell lines and human tumors is rare, arguing against a prominent tumor-suppressive role. In contrast, we have uncovered a potent tumor-promoting function for Arkadia. Using 3 different cancer cell lines whose tumorigenic properties are driven by TGF-β signaling, we show that loss of Arkadia function, either by overexpression of dominant negative Arkadia or by siRNA-induced knockdown, substantially inhibited lung colonization in tail vein injection experiments in immunodeficient mice. Our findings indicate that Arkadia is not critical for regulating tumor growth per se, but is required for the early stages of cancer cell colonization at the sites of metastasis.

Wang W, Liu C, Wang Y, Cao L
Effects of the downregulation of SnoN expression on HepG2 cell proliferation and apoptosis.
Mol Med Rep. 2013; 7(4):1324-8 [PubMed] Related Publications
Ski‑novel protein (SnoN) is a proto‑oncogene that belongs to the Ski protein family and is involved in regulating processes such as cell proliferation and apoptosis. To investigate the role of SnoN in the proliferation and apoptosis of HepG2 cells, we downregulated its expression by the use of small interfering RNA (siRNA). Three fragments predicted to have RNAi capacity were designed and synthesized as the target siRNAs (siRNA‑A, ‑B and ‑C). Following transfection, inhibition efficiency was detected by reverse transcription PCR (RT‑PCR) and western blot analysis. The siRNA with the optimal inhibition efficiency was used for the cell proliferation and apoptosis analysis. Cell proliferation was analyzed by the Cell Counting Kit‑8 (CCK‑8) and cell apoptosis was investigated by flow cytometry. In our study, all three siRNAs efficiently inhibited SnoN expression, and siRNA‑C demonstrated the optimal inhibition efficiency. We found that following downregulation of SnoN expression, HepG2 cell proliferation was significantly inhibited (P<0.05), while HepG2 cell apoptosis was significantly increased (P<0.05). SnoN‑specific siRNA is capable of effectively inhibiting the expression of SnoN in human HepG2 cells, and the downregulation of SnoN expression induces growth inhibition and apoptosis.

Jahchan NS, Ouyang G, Luo K
Expression profiles of SnoN in normal and cancerous human tissues support its tumor suppressor role in human cancer.
PLoS One. 2013; 8(2):e55794 [PubMed] Free Access to Full Article Related Publications
SnoN is a negative regulator of TGF-β signaling and also an activator of the tumor suppressor p53 in response to cellular stress. Its role in human cancer is complex and controversial with both pro-oncogenic and anti-oncogenic activities reported. To clarify its role in human cancer and provide clinical relevance to its signaling activities, we examined SnoN expression in normal and cancerous human esophageal, ovarian, pancreatic and breast tissues. In normal tissues, SnoN is expressed in both the epithelium and the surrounding stroma at a moderate level and is predominantly cytoplasmic. SnoN levels in all tumor epithelia examined are lower than or similar to that in the matched normal samples, consistent with its anti-tumorigenic activity in epithelial cells. In contrast, SnoN expression in the stroma is highly upregulated in the infiltrating inflammatory cells in high-grade esophageal and ovarian tumor samples, suggesting that SnoN may potentially promote malignant progression through modulating the tumor microenvironment in these tumor types. The overall levels of SnoN expression in these cancer tissues do not correlate with the p53 status. However, in human cancer cell lines with amplification of the snoN gene, a strong correlation between increased SnoN copy number and inactivation of p53 was detected, suggesting that the tumor suppressor SnoN-p53 pathway must be inactivated, either through downregulation of SnoN or inactivation of p53, in order to allow cancer cell to proliferate and survive. These data strongly suggest that SnoN can function as a tumor suppressor at early stages of tumorigenesis in human cancer tissues.

Kodigepalli KM, Dutta PS, Bauckman KA, Nanjundan M
SnoN/SkiL expression is modulated via arsenic trioxide-induced activation of the PI3K/AKT pathway in ovarian cancer cells.
FEBS Lett. 2013; 587(1):5-16 [PubMed] Free Access to Full Article Related Publications
SnoN/SkiL (TGFβ regulator) is dysregulated in ovarian cancer, a disease associated with acquired drug-resistance. Arsenic trioxide (As₂O₃, used in treating APL) induces SnoN to oppose the apoptotic response in ovarian cancer cells. We now report that As₂O₃ increases phosphorylation of EGFR/p66ShcA and EGFR degradation. As₂O₃ activates Src(Y416) whose activity (inhibited by PP2) modulates EGFR activation, its interaction with Shc/Grb2, and p-AKT. Inhibition of PI3K reduces SnoN and cell survival. Although EGFR or MAPK1 siRNA did not alter SnoN expression, As₂O₃-induced cleaved PARP was reduced together with increased XIAP. Collectively, As₂O₃ mediates an initial rise in pY-Src(416) to regulate the PI3K/AKT pathway which increases SnoN and cell survival; these early events may counter the cell death response associated with increased pY-EGFR/MAPK activation.

Shinozuka E, Miyashita M, Mizuguchi Y, et al.
SnoN/SKIL modulates proliferation through control of hsa-miR-720 transcription in esophageal cancer cells.
Biochem Biophys Res Commun. 2013; 430(1):101-6 [PubMed] Related Publications
It is now evident that changes in microRNA are involved in cancer progression, but the mechanisms of transcriptional regulation of miRNAs remain unknown. Ski-related novel gene (SnoN/SKIL), a transcription co-factor, acts as a potential key regulator within a complex network of p53 transcriptional repressors. SnoN has pro- and anti-oncogenic functions in the regulation of cell proliferation, senescence, apoptosis, and differentiation. We characterized the roles of SnoN in miRNA transcriptional regulation and its effects on cell proliferation using esophageal squamous cell carcinoma (ESCC) cells. Silencing of SnoN altered a set of miRNA expression profiles in TE-1cells, and the expression levels of miR-720, miR-1274A, and miR-1274B were modulated by SnoN. The expression of these miRNAs resulted in changes to the target protein p63 and a disintegrin and metalloproteinase domain 9 (ADAM9). Furthermore, silencing of SnoN significantly upregulated cell proliferation in TE-1 cells, indicating a potential anti-oncogenic function. These results support our observation that cancer tissues have lower expression levels of SnoN, miR-720, and miR-1274A compared to adjacent normal tissues from ESCC patients. These data demonstrate a novel mechanism of miRNA regulation, leading to changes in cell proliferation.

Elgaaen BV, Olstad OK, Sandvik L, et al.
ZNF385B and VEGFA are strongly differentially expressed in serous ovarian carcinomas and correlate with survival.
PLoS One. 2012; 7(9):e46317 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The oncogenesis of ovarian cancer is poorly understood. The aim of this study was to identify mRNAs differentially expressed between moderately and poorly differentiated (MD/PD) serous ovarian carcinomas (SC), serous ovarian borderline tumours (SBOT) and superficial scrapings from normal ovaries (SNO), and to correlate these mRNAs with clinical parameters including survival.
METHODS: Differences in mRNA expression between MD/PD SC, SBOT and SNO were analyzed by global gene expression profiling (n = 23), validated by RT-qPCR (n = 41) and correlated with clinical parameters.
RESULTS: Thirty mRNAs differentially expressed between MD/PD SC, SBOT and SNO were selected from the global gene expression analyses, and 21 were verified (p<0.01) by RT-qPCR. Of these, 13 mRNAs were differentially expressed in MD/PD SC compared with SNO (p<0.01) and were correlated with clinical parameters. ZNF385B was downregulated (FC = -130.5, p = 1.2×10(-7)) and correlated with overall survival (p = 0.03). VEGFA was upregulated (FC = 6.1, p = 6.0×10(-6)) and correlated with progression-free survival (p = 0.037). Increased levels of TPX2 and FOXM1 mRNAs (FC = 28.5, p = 2.7×10(-10) and FC = 46.2, p = 5.6×10(-4), respectively) correlated with normalization of CA125 (p = 0.03 and p = 0.044, respectively). Furthermore, we present a molecular pathway for MD/PD SC, including VEGFA, FOXM1, TPX2, BIRC5 and TOP2A, all significantly upregulated and directly interacting with TP53.
CONCLUSIONS: We have identified 21 mRNAs differentially expressed (p<0.01) between MD/PD SC, SBOT and SNO. Thirteen were differentially expressed in MD/PD SC, including ZNF385B and VEGFA correlating with survival, and FOXM1 and TPX2 with normalization of CA125. We also present a molecular pathway for MD/PD SC.

Bonni S, Bonni A
SnoN signaling in proliferating cells and postmitotic neurons.
FEBS Lett. 2012; 586(14):1977-83 [PubMed] Free Access to Full Article Related Publications
The transcriptional regulator SnoN plays a fundamental role as a modulator of transforming growth factor beta (TGFβ)-induced signal transduction and biological responses. In recent years, novel functions of SnoN have been discovered in both TGFβ-dependent and TGFβ-independent settings in proliferating cells and postmitotic neurons. Accumulating evidence suggests that SnoN plays a dual role as a corepressor or coactivator of TGFβ-induced transcription. Accordingly, SnoN exerts oncogenic or tumor-suppressive effects in epithelial tissues. At the cellular level, SnoN antagonizes or mediates the ability of TGFβ to induce cell cycle arrest in a cell-type specific manner. SnoN also exerts key effects on epithelial-mesenchymal transition (EMT), with implications in cancer biology. Recent studies have expanded SnoN functions to postmitotic neurons, where SnoN orchestrates key aspects of neuronal development in the mammalian brain, from axon growth and branching to neuronal migration and positioning. In this review, we will highlight our understanding of SnoN biology at the crossroads of cancer biology and neurobiology.

Band AM, Laiho M
SnoN oncoprotein enhances estrogen receptor-α transcriptional activity.
Cell Signal. 2012; 24(4):922-30 [PubMed] Free Access to Full Article Related Publications
Estrogen receptor-α (ERα) and transforming growth factor-beta (TGF-β) signaling pathways are essential regulators during mammary gland development and tumorigenesis. Ski-related novel gene (SnoN) is an oncoprotein and a negative feedback inhibitor of TGF-β signaling. We have previously reported that low expression of SnoN in ERα positive breast carcinomas is associated with favorable prognosis (Zhang et al. Cancer Res. (2003) 63, 5005-5010). Here we have studied the mechanism of a possible cross-talk between ERα and SnoN. We find that SnoN interacts with the estrogen-activated form of ERα in the nucleus. SnoN contains two highly conserved nuclear receptor binding LxxLL-like motifs and we show that mutations in these motifs reduce the interaction of SnoN with ERα. Over-expression of SnoN enhanced the transcriptional activity of ERα in estrogen response element (ERE)-reporter assays, augmented the expression of several ERα target genes and increased the proliferation of MCF7 breast carcinoma cells in an estrogen-dependent manner. Chromatin immunoprecipitation demonstrated that SnoN interacts with ERα at the TTF1 (pS2) gene promoter. Conversely, silencing of SnoN reduced both ERE-reporter activity and the expression of ERα target genes in MCF7 and T-47D breast cancer cells. Histone deacetylase inhibition increased the level of SnoN and SnoN-dependent enhancement of ERα-dependent transcription and SnoN supported the recruitment of p300 histone acetylase to ERα. This study reveals a novel mechanism that interconnects ERα and TGF-β signaling pathways by SnoN. Accordingly, the results indicate that high SnoN level promotes ERα signaling and possibly breast cancer progression.

Aranda E, López-Pedrera C, De La Haba-Rodriguez JR, Rodriguez-Ariza A
Nitric oxide and cancer: the emerging role of S-nitrosylation.
Curr Mol Med. 2012; 12(1):50-67 [PubMed] Related Publications
Nitric oxide (NO˙) is a short-lived, endogenously produced gas that is highly diffusible across cell membranes and acts as a signaling molecule in the body. The redox state and chemistry of NO˙ facilitate its interaction with various proteins thus regulating various intracellular and intercellular events. One of the key mechanisms by which NO˙ regulates the function of various target proteins is through the coupling of a nitroso moiety from NO-derived metabolites to a reactive cysteine leading to the formation of a S-nitrosothiol (SNO), a process commonly known as S-nitrosylation. S-nitrosylation signaling events within the cell have led to the discovery of many other physiological functions of NO˙ in many other types of cells including cancer cells. Only recently are the diverse roles of S-nitrosylation in cancer beginning to be understood. In the present review we discuss the recent evidence for the diverse roles of NO˙/SNO-related mechanisms in cancer biology and therapy, including the participation of NO˙ in the pathogenesis of cancer, its duality in protecting against or inducing cancer cell death and the contribution of NO˙ to metastatic processes. In addition, NO˙ can be therapeutically used in the reversal of tumor cell resistance to cytotoxic drugs and as a sensitizing agent to chemo- and radiotherapy. Finally, recent studies providing evidence for NO-related mechanisms of epigenetic gene expression regulation will also be discussed. Undoubtedly, new exciting results will contribute to this rapidly expanding area of cancer research.

Sharma V, Antonacopoulou AG, Tanaka S, et al.
Enhancement of TGF-β signaling responses by the E3 ubiquitin ligase Arkadia provides tumor suppression in colorectal cancer.
Cancer Res. 2011; 71(20):6438-49 [PubMed] Free Access to Full Article Related Publications
TGF-β signaling provides tumor protection against colorectal cancer (CRC). Mechanisms that support its tumor-suppressive properties remain unclear. The ubiquitin ligase Arkadia/RNF111 enhances TGF-β signaling responses by targeting repressors of the pathway for degradation. The corepressors SnoN/Ski, critical substrates of Arkadia, complex with the activated TGF-β signaling effectors Smad2/3 (pSmad2/3) on the promoters of target genes and block their transcription. Arkadia degrades this complex including pSmad2/3 and unblocks the promoter. Here, we report that Arkadia is expressed highly in the mouse colonic epithelium. Heterozygous Akd(+/-) mice are normal but express less Arkadia. This leads to reduced expression of several TGF-β target genes, suggesting that normal levels of Arkadia are required for efficient signaling responses. Critically, Akd(+/-) mice exhibit increased susceptibility to azoxymethane/dextran sodium sulfate carcinogen-induced CRC, as they develop four-fold more tumors than wild-type mice. Akd(+/-) tumors also exhibit a more aggressive pathology, higher proliferation index, and reduced cytostasis. Therefore, Arkadia functions as a tumor suppressor whose peak expression is required to suppress CRC development and progression. The accumulation of nuclear SnoN and pSmad2, along with the downregulation of TGF-β target genes observed in Akd(+/-) colon and tumors, suggest that tumor-suppressing properties of Arkadia are mediated by its ability to derepress TGF-β signaling. Consistent with this likelihood, we identified mutations in primary colorectal tumors from human patients that reduce Arkadia function and are associated with the accumulation of nuclear SNON. Collectively, our findings reveal that Arkadia enhances TGF-β signaling responses and supports its tumor-suppressing properties in CRC.

Nallar SC, Lin L, Srivastava V, et al.
GRIM-1, a novel growth suppressor, inhibits rRNA maturation by suppressing small nucleolar RNAs.
PLoS One. 2011; 6(9):e24082 [PubMed] Free Access to Full Article Related Publications
We have recently isolated novel IFN-inducible gene, Gene associated with Retinoid-Interferon-induced Mortality-1 (GRIM-1), using a genetic technique. Moderate ectopic expression of GRIM-1 caused growth inhibition and sensitized cells to retinoic acid (RA)/IFN-induced cell death while high expression caused apoptosis. GRIM-1 depletion, using RNAi, conferred a growth advantage. Three protein isoforms (1α, 1β and 1γ) with identical C-termini are produced from GRIM-1 mRNA. We show that GRIM-1 isoforms interact with NAF1 and DKC1, two essential proteins required for box H/ACA sno/sca RNP biogenesis and suppresses box H/ACA RNA levels in mammalian cells by delocalizing NAF1. Suppression of these small RNAs manifests as inefficient rRNA maturation and growth suppression. Interestingly, yeast Shq1p also caused growth suppression in mammalian cells. Consistent with its growth-suppressive property, GRIM-1 expression is lost in a number of human primary prostate tumors. Our observations support a recent study that GRIM-1 might act as a co-tumor suppressor in the prostate.

Javelaud D, van Kempen L, Alexaki VI, et al.
Efficient TGF-β/SMAD signaling in human melanoma cells associated with high c-SKI/SnoN expression.
Mol Cancer. 2011; 10(1):2 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: SKI and SnoN proteins have been shown to inhibit TGF-β signaling, acting both as transcriptional co-repressors in the cell nucleus, and as sequestrators of SMAD proteins in the cytoplasm. TGF-β, on the other hand, induces rapid, proteasome-mediated, degradation of both proteins. How elevated SKI and SnoN protein levels co-exist with active autocrine TGF-β signaling in cancer cells is yet to be understood.
RESULTS: In this study, we found elevated SKI and SnoN protein levels in a panel of melanoma cell lines, as compared to normal melanocytes. There was no correlation between SKI protein content and the capacity of melanoma cells to invade Matrigel™, to form subcutaneous tumors, or to metastasize to bone after intracardiac inoculation into nude mice. Nor did we find a correlation between SKI expression and histopathological staging of human melanoma. TGF-β induced a rapid and dose-dependent degradation of SKI protein, associated with SMAD3/4 specific transcriptional response and induction of pro-metastatic target genes, partially prevented by pharmacologic blockade of proteasome activity. SKI knockdown in 1205Lu melanoma cells did not alter their invasive capacity or transcriptional responses to TGF-β, and did not allow p21 expression in response to TGF-β or reveal any growth inhibitory activity of TGF-β.
CONCLUSIONS: Despite high expression in melanoma cells, the role of SKI in melanoma remains elusive: SKI does not efficiently interfere with the pro-oncogenic activities of TGF-β, unless stabilized by proteasome blockade. Its highly labile nature makes it an unlikely target for therapeutic intervention.

Elgaaen BV, Haug KB, Wang J, et al.
POLD2 and KSP37 (FGFBP2) correlate strongly with histology, stage and outcome in ovarian carcinomas.
PLoS One. 2010; 5(11):e13837 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Epithelial ovarian cancer (EOC) constitutes more than 90% of ovarian cancers and is associated with high mortality. EOC comprises a heterogeneous group of tumours, and the causes and molecular pathology are essentially unknown. Improved insight into the molecular characteristics of the different subgroups of EOC is urgently needed, and should eventually lead to earlier diagnosis as well as more individualized and effective treatments. Previously, we reported a limited number of mRNAs strongly upregulated in human osteosarcomas and other malignancies, and six were selected to be tested for a possible association with three subgroups of ovarian carcinomas and clinical parameters.
METHODOLOGY/PRINCIPAL FINDINGS: The six selected mRNAs were quantified by RT-qPCR in biopsies from eleven poorly differentiated serous carcinomas (PDSC, stage III-IV), twelve moderately differentiated serous carcinomas (MDSC, stage III-IV) and eight clear cell carcinomas (CCC, stage I-IV) of the ovary. Superficial scrapings from six normal ovaries (SNO), as well as biopsies from three normal ovaries (BNO) and three benign ovarian cysts (BBOC) were analyzed for comparison. The gene expression level was related to the histological and clinical parameters of human ovarian carcinoma samples. One of the mRNAs, DNA polymerase delta 2 small subunit (POLD2), was increased in average 2.5- to almost 20-fold in MDSC and PDSC, respectively, paralleling the degree of dedifferentiation and concordant with a poor prognosis. Except for POLD2, the serous carcinomas showed a similar transcription profile, being clearly different from CCC. Another mRNA, Killer-specific secretory protein of 37 kDa (KSP37) showed six- to eight-fold higher levels in CCC stage I compared with the more advanced staged carcinomas, and correlated positively with an improved clinical outcome.
CONCLUSIONS/SIGNIFICANCE: We have identified two biomarkers which are markedly upregulated in two subgroups of ovarian carcinomas and are also associated with stage and outcome. The results suggest that POLD2 and KSP37 might be potential prognostic biomarkers.

Jahchan NS, Luo K
SnoN in mammalian development, function and diseases.
Curr Opin Pharmacol. 2010; 10(6):670-5 [PubMed] Free Access to Full Article Related Publications
SnoN (Ski-novel protein) was discovered as a nuclear proto-oncogene on the basis of its ability to induce transformation of chicken and quail embryonic fibroblasts. As a crucial negative regulator of transforming growth factor-β (TGF-β) signaling and also an activator of p53, it plays an important role in regulating cell proliferation, senescence, apoptosis, and differentiation. Recent studies of its expression patterns and functions in mouse models and mammalian cells have revealed important functions of SnoN in normal epithelial development and tumorigenesis. Evidence suggests that SnoN has both pro-oncogenic and anti-oncogenic functions by modulating multiple signaling pathways. These studies suggest that SnoN may have broad functions in the development and homeostasis of embryonic and postnatal tissues.

Pot I, Ikeuchi Y, Bonni A, Bonni S
SnoN: bridging neurobiology and cancer biology.
Curr Mol Med. 2010; 10(7):667-73 [PubMed] Free Access to Full Article Related Publications
The transcriptional regulator SnoN has been the subject of growing interest due to its diverse functions in normal and pathological settings. A large body of evidence has established a fundamental role for SnoN as a modulator of signaling and responses by the transforming growth beta (TGFbeta) family of cytokines, though how SnoN regulates TGFbeta responses remains incompletely understood. In accordance with the critical and complex roles of TGFbeta in tumorigenesis and metastasis, SnoN may act as a tumor promoter or suppressor depending on the stage and type of cancer. Beyond its role in cancer, SnoN has also been implicated in the control of axon morphogenesis in postmitotic neurons in the mammalian brain. Remarkably, signaling pathways that control SnoN functions in the divergent cycling cells and postmitotic neurons appear to be conserved. Identification of novel SnoN regulatory and effector mechanisms holds the promise of advances at the interface of cancer biology and neurobiology.

Lasfar A, Cohen-Solal KA
Resistance to transforming growth factor β-mediated tumor suppression in melanoma: are multiple mechanisms in place?
Carcinogenesis. 2010; 31(10):1710-7 [PubMed] Free Access to Full Article Related Publications
Resistance to transforming growth factor (TGF) β-mediated tumor suppression in melanoma appears to be a crucial step in tumor aggressiveness since it is usually coupled with the ability of TGFβ to drive the oncogenic process via autocrine and paracrine effects. In this review, we will focus mainly on the mechanisms of escape from TGFβ-induced cell cycle arrest because the mechanisms of resistance to TGFβ-mediated apoptosis are still essentially speculative. As expected, some of these mechanisms can directly affect the function of the main downstream effectors of TGFβ, Smad2 and Smad3, resulting in compromised Smad-mediated antiproliferative activity. Other mechanisms can counteract or overcome TGFβ-mediated cell cycle arrest independently of the Smads. In melanoma, some models of resistance to TGFβ have been suggested and will be described. In addition, we propose additional models of resistance taking into consideration the information available on the dysregulation of fundamental cellular effectors and signaling pathways in melanoma.

Lamouille S, Derynck R
Oncogene and tumour suppressor: the two faces of SnoN.
EMBO J. 2009; 28(22):3459-60 [PubMed] Free Access to Full Article Related Publications
SnoN was first identified based on its homology with the proto-oncogene c-Ski, and has since been implicated as a promoter of oncogenic transformation and cancer progression. Consistent with a role as proto-oncogene, SnoN negatively regulates TGF-beta signalling, through its interactions with Smad complexes. Thus, SnoN inhibits the growth inhibitory effect of TGF-beta, which is considered as the basis for the tumour suppressor activity of TGF-beta signalling. In this issue of The EMBO Journal, Pan et al (2009) now demonstrate that SnoN also functions as a tumour suppressor, independently of its role in Smad signalling. The tumour suppressor role of SnoN results from its interaction with the promyelocytic leukaemia (PML) protein and the accumulation of SnoN in PML nuclear bodies, thus allowing SnoN to stabilize p53 and induce premature senescence.

Sheu JJ, Lee CH, Ko JY, et al.
Chromosome 3p12.3-p14.2 and 3q26.2-q26.32 are genomic markers for prognosis of advanced nasopharyngeal carcinoma.
Cancer Epidemiol Biomarkers Prev. 2009; 18(10):2709-16 [PubMed] Related Publications
PURPOSE: Nasopharyngeal carcinoma is an epithelial malignancy with a remarkable racial and geographic distribution. Previous cytogenetic studies have shown nasopharyngeal carcinoma to be characterized by gross genomic aberrations. However, identification of susceptible gene loci in advanced nasopharyngeal carcinoma has been poorly discussed.
EXPERIMENTAL DESIGN: A genome-wide survey of gene copy number changes was initiated with two nasopharyngeal carcinoma cell lines by array-based comparative genomic hybridization analysis. These alterations were confirmed by a parallel analysis with the data from the gene expression microarray and were validated by quantitative PCR. Clinical association of the defined target genes was analyzed by fluorescence in situ hybridization on 48 metastatic tumors.
RESULTS: A high percentage of genes were consistently altered in dosage and expression levels with gain on 3q26.2-q26.32 and losses on 3p12.3-p14.2 and 9p21.3-p23. Six candidate genes, GPR160 (3q26.2-q27), SKIL (3q26), ADAMTS9 (3p14.2-p14.3), LRIG1 (3p14), MPDZ (9p22-p24), and ADFP (9p22.1) were validated by quantitative PCR. Fluorescence in situ hybridization studies revealed amplification of GPR160 (in 25% of cases) and SKIL (33%); and deletion of ADAMTS9 (30%), LRIG1 (35%), MPDZ (15%), and ADFP (15%). Clinical association analyses indicated a poor survival rate with genetic alterations at the defined 3p deletion (P = 0.0012) and the 3q amplification regions (P = 0.0114).
CONCLUSION: The combined microarray technologies suggested novel candidate oncogenes, amplification of GPR160 and SKIL at 3q26.2-q26.32, and deletion of tumor suppressor genes ADAMTS9 and LRIG1 at 3p12.3-p14.2. Altered expression of these genes may be responsible for malignant progression and could be used as potential markers for nasopharyngeal carcinoma.

Pan D, Zhu Q, Luo K
SnoN functions as a tumour suppressor by inducing premature senescence.
EMBO J. 2009; 28(22):3500-13 [PubMed] Free Access to Full Article Related Publications
SnoN represses TGF-beta signalling to promote cell proliferation and has been defined as a proto-oncogene partly due to its elevated expression in many human cancer cells. Although the anti-tumourigenic activity of SnoN has been suggested, the molecular basis for this has not been defined. We showed here that high levels of SnoN exert anti-oncogenic activity by inducing senescence. SnoN interacts with the promyelocytic leukaemia (PML) protein and is recruited to the PML nuclear bodies where it stabilizes p53, leading to premature senescence. Furthermore, overexpression of SnoN inhibits oncogenic transformation induced by Ras and Myc in vitro and significantly blocks papilloma development in vivo in a carcinogen-induced skin tumourigenesis model. The few papillomas that were developed displayed high levels of senescence and spontaneously regressed. Our study has revealed a novel Smad-independent pathway of SnoN function that mediates its anti-oncogenic activity.

Nanjundan M, Cheng KW, Zhang F, et al.
Overexpression of SnoN/SkiL, amplified at the 3q26.2 locus, in ovarian cancers: a role in ovarian pathogenesis.
Mol Oncol. 2008; 2(2):164-81 [PubMed] Free Access to Full Article Related Publications
High-resolution array comparative genomic hybridization of 235 serous epithelial ovarian cancers demonstrated a regional increase at 3q26.2 encompassing SnoN/SkiL, a coregulator of SMAD/TGFbeta signaling. SnoN RNA transcripts were elevated in approximately 80% of advanced stage serous epithelial ovarian cancers. In both immortalized normal (TIOSE) and ovarian carcinoma cell lines (OVCA), SnoN RNA levels were increased by TGFbeta stimulation and altered by LY294002 and JNK II inhibitor treatment suggesting that the PI3K and JNK signaling pathways may regulate TGFbeta-induced increases in SnoN RNA. In TIOSE, SnoN protein levels were reduced 15min post TGFbeta-stimulation, likely by proteosome-mediated degradation. In contrast, in OVCA, SnoN levels were elevated 3h post-stimulation potentially as a result of inhibition of the proteosome. To elucidate the role of SnoN in ovarian tumorigenesis, we explored the effects of both increasing and decreasing SnoN levels. In both TIOSE and OVCA, SnoN siRNA decreased cell growth between 20 and 50% concurrent with increased p21 levels. In TIOSE, transient expression of SnoN repressed TGFbeta induction of PAI-1 promoters with little effect on the p21 promoter or resultant cell growth. In contrast to the effects of transient expression, stable expression of SnoN in TIOSE led to growth arrest through induction of senescence. Collectively, these results implicate SnoN levels in multiple roles during ovarian carcinogenesis: promoting cellular proliferation in ovarian cancer cells and as a positive mediator of cell cycle arrest and senescence in non-transformed ovarian epithelial cells.

Wu K, Katiyar S, Witkiewicz A, et al.
The cell fate determination factor dachshund inhibits androgen receptor signaling and prostate cancer cellular growth.
Cancer Res. 2009; 69(8):3347-55 [PubMed] Free Access to Full Article Related Publications
Initially isolated as the dominant suppressor of the mutant epidermal growth factor receptor (ellipse), the Dachshund gene plays a key role in metazoan development regulating the Retinal Determination Gene Network. Herein, the DACH1 gene was expressed in normal prostate epithelial cells with reduced expression in human prostate cancer. DACH1 inhibited prostate cancer cellular DNA synthesis, growth in colony forming assays, and blocked contact-independent growth in soft agar assays. DACH1 inhibited androgen receptor (AR) activity, requiring a conserved DS Domain (Dachshund domain conserved with Ski/Sno) that bound NCoR/HDAC and was recruited to an androgen-responsive gene promoter. DACH1 inhibited ligand-dependent activity of AR mutations identified in patients with androgen-insensitive prostate cancer. The DS domain was sufficient for repression of the AR wild-type but failed to repress an AR acetylation site point mutant. These studies show a role for the Retinal Determination Gene Network in regulating cellular growth and signaling in prostate cancer.

Boone B, Brochez L
Clinical markers and driving mechanisms in melanoma progression: VEGF-C, RhoC, c-Ski/SnoN and EGFR.
Verh K Acad Geneeskd Belg. 2009; 71(5):251-94 [PubMed] Related Publications
This research project aimed at evaluating the clinical and prognostic value of different molecules involved in signalling transduction pathways involved in melanoma progression. Vascular endothelial growth factor-C or VEGF-C induces lymphangiogenesis. This study showed high VEGF-C expression to be associated with the presence of a positive sentinel lymph node. The presence of VEGF-C expression in melanoma cells was associated with reduced disease free and overall survival. RhoC is important in the organization of the actin filamental system. We observed RhoC mRNA and protein expression to be upregulated in a highly metastatic melanoma cell line (DX3aza), whereas only low expression levels were found in a melanoma cell line with low proliferative and invasive capacity (MeWo). RhoC immunoreactivity in melanoma tissue was associated with high Breslow tumour thickness and the presence of ulceration. C-Ski and SnoN have been identified as negative regulators in the TGF-beta pathway. We found a significant association between the presence of nuclear c-Ski and thicker, ulcerated melanomas. SnoN expression was associated with the presence of ulceration and a positive sentinel lymph node. Epidermal Growth Factor Receptor (EGFR) expression has been associated with tumour progression and poor outcome in a variety of solid tumours, EGFR immunoreactivity was more frequently present in patients with a positive sentinel lymph node. EGFR gene amplification was not observed; however, the presence of polysomy was associated with higher Breslow tumour thickness. Treating BLM melanoma cells with different concentrations of cetuximab reduced the invasive capacity of the melanoma cells, without impact on cell viability and growth.

Bravou V, Antonacopoulou A, Papadaki H, et al.
TGF-beta repressors SnoN and Ski are implicated in human colorectal carcinogenesis.
Cell Oncol. 2009; 31(1):41-51 [PubMed] Related Publications
BACKGROUND: The TGF-beta signaling repressors SnoN and Ski have been critically implicated in human cancer.
METHODS: To explore the role of SnoN and Ski in the development and progression of colorectal cancer we examined their protein expression profile by immunohistochemistry in a series of human colorectal adenomas, carcinomas and lymph node metastases. The mRNA expression of SnoN was also quantified by Real-Time RT-PCR.
RESULTS: SnoN and Ski were overexpressed both in adenomas with severe dysplasia and colorectal carcinomas. Protein expression was cytoplasmic and nuclear with predominant cytoplasmic localization. The subcellular localization was related differently to pathologic variables of colorectal carcinomas. Although there was no significant association of protein levels with tumor invasion and metastasis, a significant correlation of nuclear SnoN and Ski with beta-catenin pathway was observed. Moreover, SnoN mRNA did not differ in carcinomas as compared to normal control and there was no correlation between SnoN protein and mRNA levels.
CONCLUSION: Our findings suggest that SnoN and Ski exert oncogenic effects in human colorectal carcinogenesis and their overexpression is implicated in early stage disease.

Zhang W, Ding J, Qu Y, et al.
Genomic expression analysis by single-cell mRNA differential display of quiescent CD8 T cells from tumour-infiltrating lymphocytes obtained from in vivo liver tumours.
Immunology. 2009; 127(1):83-90 [PubMed] Free Access to Full Article Related Publications
We performed a genomic study combining single-cell mRNA differential display and RNA subtractive hybridization to elucidate CD8 T-cell quiescence/ignorance. By comparing actively maintained quiescent CD8 T cells from liver tumour tumour-infiltrating lymphocytes (TILs) with quiescent T cells at the single-cell level, we identified differentially expressed candidate genes by high-throughput screening and comparative analysis of expressed sequence tags (ESTs). While genes for the T-cell receptor, tumour necrosis factor (TNF) receptor, TNF-related apoptosis inducing ligand (TRAIL) and perforin were down-regulated, key genes such as Tob, transforming growth factor (TGF)-beta, lung Krüpple-like factor (LKLF), Sno-A, Ski, Myc, Ets-2 repressor factor (ERF) and RE1-silencing transcription factor (REST/NRSF) complex were highly expressed in the quiescent TIL CD8 cells. Real-time polymerase chain reaction (PCR) further confirmed these results. A regulation model is proposed for actively maintained quiescence in CD8 T cells, including three components: up-regulation of the TGF-beta pathway, a shift in the MYC web and inhibition of the cell cycle.

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