| BackgroudCancer is a highly lethal disease that is often diagnosedin an advanced state.Amajorhallmark of cancer is extensive local tumor invasion, early systemic disseminationand notoriously resistant to chemotherapy and ionizing radiation.Therefore, it is of greatimportance to further understand the molecular pathogenesis of cancer by employinggenomic, epigenetic and proteomic profiling to identify differentially expressed genes andproteinsthat might represent novel diagnostic and therapeutic targets.The epigenetic silencing of tumor suppressor genes is a crucial event duringcarcinogenesis. The term ‘‘epigenetics’’ was originally used to describe heritable changesin a cellular phenotype that were independent of alterations in the DNA sequence. DNAmethylation, histone modification, nucleosome remodeling, and RNA-mediated targetingregulate many biological processes that are fundamental to the genesis of cancer. Inparticular, DNA methylation plays an important role in the development and progression ofcancer. Cancer epigenome is characterized by global DNA hypomethylation andpromoter-specific hypermethylation, including CpG island promoterhypermethylation–associated silencing of tumor suppressor genes and aberranthypomethylation induced activation of some protooncogenes. Methylation induced silenceof tumor suppressor genes is known to provoke aberrant gene expression patterns whichexist in all the signaling pathway and give rise to all typical cancer characteristics.Therefore, promoter methylation pattern is a good marker to find novel aberrant geneexpression changes. We screened genome wide for novel methylated genes and identifiedSRY-box containing gene10(SOX10), located at chromosome22q13.1, as one of themethylated targets.SOX10is a member of the high mobility group (HMG) transcription factorsuperfamily, which was first identified by homology to the HMG box of thesex-determining gene Sry. SRY and SOX proteins are thought to regulate genetranscription through binding to specific DNA sequence motifs and causing the DNA tobend-a property of so called architectural transcription factors. Based on phylogeneticanalysis of their HMG domains, Sox genes can be separated into subgroups A-J. Sox8,Sox9and Sox10belong to the SoxE group. Sox family genes are evolutionarily conservedand appear to play important functions during the steps leading to modulating cell stemness, specification and differentiation. SOX10gene has emerged as an importantplayer in regulating multiple aspects of neural crest development, nervous systemneurogenesis, differentiation of oligodendrocyte, glia and melanocytes. Mutations in Sox10gene have also been linked with the occurrence of neurocristopathies in theWaardenburg-Shah and Waardenburg-Hirschsprung.Dysregulation of SOX factors have been further implicated in multiple diseasesincluding cancer. Some studies have shown that SOX2, SOX3, SOX4and SOX95areup-regulated and possess oncogene function in different types of cancers. However, SOX1,SOX7, SOX11and SOX17have been demonstrated to be tumor suppressors. Until now,the expression and functional role of SOX10in cancer development has been unclear. Inthis study, we validated the antibody against human SOX10protein with high-specificity.Immunohistochemistry is used to detect the expression profile of SOX10in clinicalspecimens from diverse human cancer tissues. We employed lentivirus to elevate theexpression of SOX10in gastric carcinoma AGS, esophageal carcinoma KYSE150andcolorectal carcinoma HCT116cell lines and assess its effects on tumor cell migration andinvasion potential in vitro and in nude mice.Results1. Cell immunofluorescence and western blotting confirmed the specificity of the mouseantibody targeting SOX10.We next analyzed SOX10expression using human normaltissue microarrays carrying24different tissue types. SOX10was normally expressed inbrain, colon, small intestine, lung, prostate, breast, esophagus, stomach, pancreas, heart andtestis and, to a lesser extent, in liver and lung, in perfect conformity with its RNA level. Inthe normal tissues, immunopositive staining of SOX10was detected in the nucleus ofepithelial cells. SOX10expression was decreased or completely silenced in multipleprimary carcinomas with variable frequencies. Downregulation of SOX10was frequentlydetected in51%(20of39) of esophageal,68%(23of34) of gastric,51%(20of39) ofcolorectal carcinoma. These results suggest that down-regulation of SOX10expression is acommon event in multiple tumorigenesis.2. AGS, KYSE150and HCT116cells infected with LV-SOX10filled in the wound muchslower than LV-GFP infected cells. Up-regulation of SOX10also markedly inhibited cellmigration through a permeable filter as well as matrigel. SOX10also significantlyrepressed lung metastasis and establishment of colorectal cancer liver metastasis in nude mice. Besides, SOX10was a potent EMT inhibitor and repressed EMT-associated stem cellproperties,3. SOX10specifically inhibits β-catenin transactivation and CCND1, c-Myc and MMP7,which are typical transcriptional targets of the Wnt/β-catenin/TCF signaling pathway in adose-dependent manner.SOX10competitively displaces TCF4from binding to β-catenin.SOX10directily interacted with β-catenin viaDVAELDQYL motif. SOX10was recruitedto Wnt/β-catenin promoter and transrepressed target genes via its HMG domain.4. Ectopic expression of SOX10in cancer cells grew and migrated significantly slowerthan control cells, whereas introduction of SOX10-DB or SOX10-3G partially restoredtheir proliferation as well as migration potential as demonstrated by colony formation andtranswell assay, suggesting that interaction of SOX10with β-catenin is, at least in part,required for its tumor suppressor function.Conclusion1．The expression of SOX10was diminished in diverse human primary tumors, indicatingthe critical role of SOX10in the development and progression of cancer.2．Restoring SOX10expression in SOX10-deficient cancer cells inhibits their metastaticpotential invitro and in nude mice. SOX10also suppressed epithelial to mesenchymaltransition and stemness properties, suggesting SOX10functions as a tumor suppressor genein cancers.3．SOX10competes with TCF4to bind β-catenin and transrepresses its downstream targetgenes via its own DNA-binding property. Hence, SOX10is an important regulator ofWnt/β-catenin signaling.SOX10is a commonly inactivated tumor suppressor in cancers from different tissueorigins by inhibiting cell motility and invasion as well as EMT through repressingWnt/β-catenin signaling. The study provides a new insight into the molecular mechanismsleading to carcinogenesis. |
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