P-41: Comparing the Expression of miR-302, an ESC-specific MicroRNA, and miR-145 in Tumor and Non-tumor Samples of Stomach
Objective: According to the cancer stem cell hypothesis, a subpopulation of tumor cells has the capacity for self-renewal, with unlimited proliferation potential. Recently, increasing evidence suggest that, a novel class of molecules, termed microRNAs (miRNAs), are involved in various biological processes including self-renewal and differentiation of embryonic and tissue-specific stem cells, apoptosis and tumorigenesis. Alteration in miRNAs expression is observed in several human cancers suggesting that these molecules have a potential role in tumor initiation or progression. The miR-302 and miR-145 are two main regulatory factors of reprogramming. Functionally, miR-302 gene regulates self-renewal and pluripotency in ESCs, and therefore represents a master regulatory role in the maintenance of human ESCs (hESCs) stemness. There is new evidence that miR-145 has probably a tumor suppressor activity, and its expression is downregulated in some cancers. For these reasons, we aim to determine and compare the expression of miR-302 and miR-145 miRNAs in gastric tumor and non-tumor samples. Materials and Methods: Tumor and non-tumor (apparently normal tissues from the margin of same tumors, as control) surgical specimens from 36 patients with gastric adenocarcinoma were obtained from the Iran National Tumor Bank. Total RNA was extracted from the homogenized tissue specimens using Trizol solution. Using miRCURY LNA™ Universal RT microRNA PCR kit (Exiqon), miR-145 and miR-302 were amplified by real-time PCR. Results: The relative expression of miR-145 and miR-302 was normalized to that of U6 housekeeping gene. According to our data, the expression level of miR-302 and miR-145 didn't show a significant difference between tumor and non-tumor samples of stomach. We also compared the expression level of miR-302 and miR-145 in different grades of gastric samples (I, II and III grades) but no significant difference observed in low and high grade tumors. Conclusion: Re-expression of some stem cell-specific genes has been already reported in some cancers. Furthermore, based on our unpublished observation, the expression of miR-302 is restricted to a subpopulation of glioma cell lines with stem cell properties. Our current data suggest that the expression levels of miR-302 and miR-145 could neither differentiate between tumor and non-tumor state of samples nor among different grades of the malignancy.