X-ray Radiation Alters MiRNA Expression Profile In Gastric Cancer

Gastric cancer is the most common cancer in China, the incidence and mortality rate of gastric cancer ranks first in all kind of malignant tumors. Until now, surgical operation is the most important way to treat gastric cancer. However, limited by diagnostic method, most of the therapy can not be cured completely because of optimal cure time losing. Furthermore, multidrug resistance of cancer cells also affected the use of chemotherapy. Thus, it is quite necessary to find a new way to diagnose and cure gastric cancer. Now, it has been reported that it is markedly enhanced the effect by surgery accompanied with radiotherapy.microRNA (miRNA) is a new class of endogenous non-coding small RNAs with 19-25nt length. miRNA regulates various cell processes, and aberrant expression of some miRNAs in cancers implies that they act as oncogenes or tumor suppressor genes. Furthermore, miRNA is concerning with numbers of cell stress reaction. Thus, we postulated that miRNA might be a kind of new biomarker for early-stage gastric cancer diagnosis and included in gastric cancer cell radiation response. Until now, there has been no report on the potential roles of miRNA in gastric cancer cell radiation response.In this study, we compared the miRNA expression profiles between gastric cancer tissues and the corresponding gastric normal tissues with miRNA microarray. On the other hand, the effects of the X-ray irradiation on gastric cancer miRNA expression were studied. The results showed that 17 miRNAs including let-7 and miR-300 were over-expressed while 9 miRNAs were down-regulated in gastric cancer. Upon irradiation with 4 Gy of X-ray,16 miRNAs were down-regulated; moreover,7 miRNAs out of 16 miRNAs were up-regulated in gastric cancer. The miRNAs with changed expression level were classified 3 categories basing on the results of cluster analysis, among which miR-300 was chosen for further studies.6 out of 10 irradiated gastric cancer tissues were found to have suppressed expression of miR-300 by using real-time RT-PCR. Putative target genes of miR-300 as predicted in miRBase are key factors playing important roles in varieties of cell progresses including apoptosis, cell cycle regulation, and DNA repair. So it suggested that miR-300 plays important roles in gastric cancer cell radiation response.In summary, our results demonstrated that miR-300 expression level was significantly increased in gastric cancer, while its expression was suppressed by X-ray dramatically. Moreover, the putative target genes of miR-300 may play critical roles in various cell processes.