Epigenetic Identification Of Mitogen-activated Protein Kinase10as A Functional Tumor Suppressor And Its Clinical Significance In Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethalmalignancies for humans. Given that patients with HCC are alwaysdiagnosed at the advanced stage and HCC is one of the well identifiedcancers that are most resistant to systemic chemotherapy, efficacy ofcurative surgery or chemotherapy on HCC remains very poor, whichhighlights the need for reliable biomarkers in the early diagnosis of HCC.As for many other tumors, development of HCC is the consequence of amultistep process with genetic and epigenetic alterations in regulatorygenes, resulting in activation of oncogenes and inactivation of TSG.Promoter CpG methylation, one of the epigenetic alterations which occurfrequently during tumor development and progression, causes the loss ofTSG functions. Recent studies have evidenced the importance of promoterCpG methylation in initiating carcinogenesis and it has been hypothesizedthat TSG methylation can be used as epigenetic biomarkers for tumor diagnosis or prognosis prediction clinically. To find more valuable TSGsfrequently methylated in HCC and establish a specific methylation profilewould be helpful to provide new and reliable biomarkers for HCCmanagement.Mitogen-Activated Protein Kinase10(MAPK10) is a member of thec-Jun N-terminal kinases (JNK) subgroup in MAP kinase superfamily,recently suggested as a tumor suppressor inactivated epigenetically. Here,we investigated its role as a tumor suppressor in HCC from the epigeneticway. MAPK10was expressed in almost all normal tissues including liver,however, it was low or silenced in67%(8/12) of HCC cell lines. For thoseclinical samples, MAPK10expression was also significantly lower in HCCthan that in adjacent non-tumor tissues (63%,29/46; p=0.000, Wilcoxonsigned rank test). Promoter methylation of MAPK10was further detectedin58%(7/12) of the HCC cell lines and in66%(12/18) of primary HCCtissues by methylation specific PCR (MSP), which was well correlated withits silenced or downregulated expression. Moreover, the transcriptionalsilencing of MAPK10could be reversed by pharmacologic demethylationand ectopic expression of MAPK10in silenced HCC cell lines couldsignificantly inhibit colony formation ability, induce apoptosis or enhancethe chemosensitivities of HCC cells to5-Fu. In addition, the expression ofp53, caspase3and caspase8could be increased after the ectopicexpression of MAPK10in these silenced HCC cells. Finally, the clinical significance of MAPK10in a cohort of59HCC cases was assessed. Inthese cases examined, negative expression of MAPK10was significantlyassociated with advanced tumour stage (p=0.001), more microsatellitenodules (p=0.025), higher serum AFP (p=0.05) and shorter overall survivaltime of HCC patients (p=0.008).Thus, MAPK10appears to be a functional tumor suppressor gene (TSG)frequently methylated in HCC, which could be a valuable biomarker or anew therapy target clinically.