Role And Mechanism Of MiR-497 In Colorectal Tumor Growth And Drug Sensitivity

Colorectal cancer(CRC)is one of the most prevalent carcinomas throughout the world,with an estimated one million new cases and half a million mortalities each year.The 5-year overall survival rate ranges from 40% to 60%.In present,advances in diagnostic and therapeutic approacheshave led to excellent expectations for long-term survival of CRC,but there are still a significant proportion of patients who experience drug resistant,relapse and poor outcomes.At the molecular level,colorectal cancer may arise from a series of genetic and epigenetic alterations that inactivate tumor suppressor genes and activate oncogenes.However,the basic mechanisms underlying CRC initiation and progression remain largely unknown.Better understanding of the molecular mechanisms underlying carcinogenesis,progression and drug resistance in CRC is useful in improving diagnosis,treatment and prevention.MicroRNAs(miRNAs)are endogenous small non-coding RNAs which act as negative regulators for mRNA expression via sequence-complementary targeting of the 3'-untranslated regions(3'-UTRs)to repress translation or mediate mRNA degradation.Due to their abundance and divergence of targeting specificity,it is believed that one single miRNA can interact with multiple mRNA targets to achieve regulatory control over virtually every biological process.A variety of studieshave reported that miRNAs play critical roles in cell growth,differentiation,apoptosis and tumourigenesis,They can potentially act as oncogenes or tumor-suppressor genes in a variety of tumors,including colorectal cancer.Among them,miR-497 has been demonstrated to function as a tumor suppressor,and loss of miR-497 expression has been reported in many cancer types,restoration of miR-497 expressionhas been shown to abrogate tumorigenesis.Current known miR-497 target genes are IGF-IR,eIF4 E,SMURF1 and Bcl2 that may be involved in pathogenesis of cancers.We detected miR-497 expression levels in 62 pairs of CRC specimens and corresponding adjacent normal tissues by qRT-PCR method,and combined with clinical features for further analysis.In CRC,miR-497 was downregulated in tumor tissues compared with para-carcinoma tissues,and the expression levels of miR-497 were correlated with clinical stages.We constructed stable cell lines expressing miR-497,studied the role of miR-497 in tumor development,and found that overexpression of miR-497 significantly inhibited cell growth rate,migration and invasion.To further study the molecular mechanism of its function,we predicted the potential targets of miR-497 by bioinformatics softwares and demonstrated that miR-497 suppressed tumor growth by directly targeting oncogene KSR1.We also discovered that overexpression of miR-497 enhanced chemosensitivity of CRC cells to 5-Fu treatmet which indicated the important role of miR-497 in CRC drug resistance.Finally,to demonstrate the effect of miR-497 in CRC,we dfound the tumor growth in nude mice was dramatically suppressed by miR-497.Taken together,the expression levels of miR-497 were closely correlated with the CRC clinical stages,and miR-497 suppressed the tumor development of CRC by directly targeting KSR1.We found that miR-497 inhibited CRC tumor developmentthrough targeting KSR1,and increased the sensitivity of CRC to 5-Fu treatment.This study indicated that miR-497 may be a novel biomarker for diagnosis and prognosis of CRCs,as well as a potential new therapeutic target.