MiR-129-5p inhibits proliferation of gastric cancer cells through targeted inhibition on HMGB1 expression.

OBJECTIVE The aim of this study was to investigate the effects of micro ribonucleic acid (miR)-129-5p on the proliferation and apoptosis of gastric cancer cells via targeted repression on the expression of high mobility group protein B1 (HMGB1). PATIENTS AND METHODS Expression levels of miR-129-5p and HMGB1 in gastric cancer tissues (n=25) and adjacent normal tissues were measured via reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The regulatory effect of miR-129-5p on the proliferation of gastric cancer MGC-803 and SGC7901 cells was determined through Cell Counting Kit-8 (CCK-8) assay. Flow cytometry was employed to analyze the apoptosis rate of gastric cancer cells. To further discover the mechanism of miR-129-5p in regulating malignant behaviors of gastric cancer cells, the miRDB database was employed to predict the binding targets of miR-129-5p. Finally, binding sites of HMGB1 3'-untranslated region (3'-UTR) to miR-129-5p were discovered. Subsequently, HMGB1 wild-type or mutant 3'-UTR Luciferase reporter vectors were constructed, and transfected to MGC-803 and SGC7901 cells together with miR-129-5p or negative control miRNA. Next, Western blotting was adopted to measure the protein expression level of HMGB1 in MGC-803 and SGC7901 cells transfected with miR-129-5p or negative control miRNA, so as to investigate whether miR-129-5p affected HMGB1 protein expression. Additionally, to determine whether HMGB1 mediated the regulatory effect of miR-129-5p on the proliferation of gastric cancer cells, MGC-803 and SGC7901 cells were transfected with pcDNA-HMGB1 or pcDNA-vector, respectively. The expression level of HMGB1 was measured via RT-qPCR, and cell proliferation was determined by CCK-8 assay. RESULTS The expression level of miR-129-5p in gastric cancer tissues was significantly lower than that in adjacent normal tissues (p<0.001). Meanwhile, the level of miR-129-5p was overtly lower in gastric cancer MGC-803 and SGC7901 cell lines than that in normal gastric mucosal epithelial GES-1 cells (p<0.001). These results indicated that miR-129-5p was lowly expressed in gastric cancer tissues and cell lines. Subsequent results demonstrated that the expression of HMGB1 increased remarkably in gastric cancer tissues compared with normal adjacent tissues (p<0.05). The proliferation ability of MGC-803 (p<0.001) and SGC7901 (p<0.01) cells with over-expressed miR-129-5p was remarkably weakened. Overexpression of miR-129-5p distinctly promoted the apoptosis rate of gastric cancer MGC-803 (p<0.01) and SGC7901 (p<0.001) cells. Moreover, miR-129-5p up-regulation significantly reduced the Luciferase activity of wild-type HMGB1 (p<0.001). However, no significant effect was observed on that of mutant HMGB1. The results suggested that overexpression of miR-129-5p significantly down-regulated the level of HMGB1 in gastric cancer cells. In addition, the messenger RNA (mRNA) level of HMGB1 in cells transfected with miR-129-5p also decreased significantly (p<0.001). HMGB1 overexpression overtly reversed the inhibitory effect of miR-129-5p on the proliferation of gastric cancer cells (p<0.05). All these results demonstrated that the miR-129-5p/HMGB1 axis played a key role in regulating the growth of gastric cancer cells. CONCLUSIONS MiR-129-5p suppresses the progression of gastric cancer through targeted inhibition on the expression of HMGB1.