The Mechanism Of MiR-24 Promoting Tumor Growth By Targeting BCL2L11 In Gastric Cancer

Background and objective: Gastric cancer(GC) is one of the most common malignancies worldwide, and the prognosis is poor; however, the molecular mechanism in tumorigenesis still needs exploration. Cell apoptosis occur during the whole process of cancer development, thus the aberrant of apoptosis pathway may play an important role in GC tumorigenesis. BCL2L11 belongs to the BCL-2 family, and acts as a central regulator of the intrinsic apoptotic cascade and mediates cell apoptosis. The aberrant expression of BCL2L11 has been discovered in many diseases, including cancer, but the mechanisms need further exploration. Micro RNAs(miRNAs) cause negative regulation of their target genes, thus involving in many biological processes, such as cancer development and chemoresistance. Our previous studies have discovered that there exists special miRNA expression profile in GC, but the underlying mechnisims are still unclear. This study aimed to explore the expression of BCL2L11 in GC, select miRNAs which directly target BCL2L11 and further discuss the role of the miRNA-BCL2L11 pathway in the tumorigenesis of GC.Methods: 1. Target prediction: By using bioinformatics tools, we found that miR-24 can directly target the 3'UTR of BCL2L11 m RNA. 2. The tissues experiments Gastric cancer tissues and paired adjacent noncancerous tissues were collected, and the expression of BCL2L11 and miR-24 was detected thereafter. 3. In vitro The direct evidence of the interaction between miR-24 and BCL2L11 was given by luciferase assay. The expression levels of BCL2L11 were determined after the overexpression or knockdown of miR-24 in SGC7901 cells. And the CCK8 assays, transwell, wound healing methods and cell flow assays were performed to verify the functional role of miR-24 in GC cells. Then we overexpressed miR-24 and BCL2L11 simultaneously to give more evidence. Furthermore, si RNA was used to knock-down BCL2L11 to explore BCL2L11-involved pathway in GC cells.4. In vivo SGC7901 cells treated with control lentivirus or miR-24 overexpressing lentivirus or BCL2L11 overexpressing lentivirus were injected subcutaneously into nude mice. Mice were sacrificed after 4 weeks, and the weight and diameter of tumors were recorded. The expression of BCL2L11 and miR-24 were determined thereafter.Results: 1. Compared with noncancerous tissues, the expression of BCL2L11 protein showed clear decrease in GC; however, its m RNA levels did not differ significantly. And miR-24 showed obvious increase in all the tumor tissues. 2. The luciferase assay showed that miR-24 can directly bind to the 3'UTR of BCL2L11 m RNA. The overexpression of miR-24 by transfection of mimics leads to the clear suppression of BCL2L11 protein, but not BCL2L11 m RNA. While the transfection of miR-24 inhibitors enhances the expression of BCL2L11. The subsequent functional experiments demonstrated that miR-24 promoted proliferation, invasion while inhibited apoptosis of GC cells. Overexpression of BCL2L11 partly reduced miR-24-induced GC cell growth. Furthermore, BCL2L11 si RNA leads to a sharp decrease in protein expression, thus significantly suppressing cell apoptosis and promoting cell proliferation. 3. In vivo experiments, overexpression of miR-24 increases tumor size and weight obviously; while the overexpression of BCL2L11 strongly inhibits tumor growth. And the BCL2L11 protein was dramatically inhibited in the miR-24 overexpression group, while the BCL2L11 m RNA was not changed.Conclusion: In the present study, miR-24 was found to be up-regulated while the expression of BCL2L11 was inhibited in tumor tissues of GC. Studies from both in vitro and in vivo shown that miR-24 regulates BCL2L11 expression by directly binding with 3'UTR of m RNA, thus promoting cell growth, migration while inhibiting cell apoptosis. Therefore, miR-24 is a novel onco-miRNA that can be potential drug targets for future clinical use.