The Screening And Functions Of MicroRNA Markers In Colorectal Cancer

Background information: Colorectal cancer (CRC) is one of the most commonlydiagnosed gastrointestinal cancer types. Annually, more than one million new casesoriginate worldwide. The primary CRC which exists in the intestinal wall could bedetected by endoscopy and often shows good outcomes after surgery orchemotherapies. The5-year survival rate is almost90%, even in developed countries,the overall fatality rate of colorectal cancer is up to33%. Although detectablemetastasis is not observed in adjacent lymph nodes, the recurrence rate also reach25%. Due to metastasis always leads to death. Therefore, the detection andappropriate therapies in early stage is critical for the survival of CRC patients. Despitethe conventional histopathological staining, the biomarkers of CRC are anotherimportant parameter for accurate prognosis and prediction. The utilization ofmolecular markers has a lot of advantages in diagnosis and prognosis. However, thepotential protein markers frequently involve in cancer cell proliferation and apoptosissignal pathways. Thus, the candidates were often impacted by somatic mutations,which amplify the difficulty of detection and results indeterminacy. In addition, theever-present individual differences is another obstacle for the application. Karyotypeanalysis is in the same boat. Complicated detection and poor individual repeatabilitymakes it as the subordinate options for routinely pathologic examinations, and rarelycontributes to diagnosis and prediction. miRNA has been discovered and chosen asthe molecular marker of cancer in recent years. The superiority are easy detection, lowcost and high sensitivity. Therefore, the purpose of this research is to screen andobtain miRNA which specifically express in CRC tissues, then try to illuminate itsbio-functions and clinical significance.Methods: Firstly, we attempted to screen the differently expressed miRNAs in5CRCtissues via microRNA array. Then, we further testified the miRNA expression in other30CRC tissues and several colorectal cancer cell lines by Realtime-PCR. Therelationship between CRC stage and miRNA expression level also had been measured. The following study focussed on the miRNA functions in colorectal cancer cell lineHCT-116. To investigate the mechanism of regulatory activity, we have to find outtarget genes of the miRNA which was predicted by web database. Then luciferasereporter gene system, Realtime-PCR and immunoblot were performed to verify theresults. And we also assessed the regulatory effects of the miRNA and its target genesin HCT-116cell. Finally, we built the mouse colorectal carcinoma cell xenograftsmodel and reveal the miRNA functions in vivo.Results: The miRNA array pointed out that miR-103was highly expressed incolorectal cancer tissues than relevant adjacent tissues. Realtime-PCR showed thesame result: miR-103level was higher in other30CRC tissues than normal tissues,and it also works in the contrast between CRC cell lines and normal colonic cell line.Meanwhile, miR-103expression was closely related to the tumor metastasis and TNMstage among the CRC clinical specimens. We then identified that miR-103couldpromote cell proliferation and invasion in CRC cell line HCT-116. Subsequently wepredicted miR-103target genes by web database, and the assumption was testified byluciferase reporter assay, Realtime-PCR and immunoblot. As the target genes of miR-103, DICER and PTEN inhibitory regulation of cell proliferation and migration couldbe compromised by miR-103overexpression. Finally, in vivo, the xenografts mousemodel showed consistent results, miR-103overexpression caused bigger solid tumorsand decrease of miR-103could repress the tumor growth significantly.Conclusion: In conclusion, we found that miR-103is up-regulated in colorectalcancers and its overexpression is closely associated with tumor proliferation andmigration. In addition, we explored the molecular mechanism by which miR-103contribute to cell proliferation and migration via its target genes DICER and PTEN,and confirmed that in vitro and in vivo. Our data collectively demonstrated that miR-103is an oncogene miRNA that promotes colorectal cancer proliferation andmigration through down-regulation of the tumor suppressor genes DICER and PTEN.Thus, miR-103may represent a new potential diagnostic and therapeutic target forcolorectal cancer treatment.