MiR-138 Suppresses Cell Proliferation by Targeting Bag-1 in Gallbladder Carcinoma

BACKGROUND MiR-138 is frequently downregulated in different cancer types and is thought to be involved in the progression of tumorigenesis. However, the molecular mechanism of miR-138 involvement in gallbladder carcinoma still remains unknown. METHODS The expression of miR-138 in 49 gallbladder carcinoma samples and paired normal gallbladder samples was analyzed using quantitative reverse transcription-polymerase chain reaction. The biological functions of miR-138 and Bag-1 (Bcl-2-associated athanogene-1) on cell proliferation were examined using 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide and apoptosis assays. Targets of miR-138 were predicted using bioinformatics and validated using luciferase reporter and Western blot analyses. The in vivo effects of miR-138 were examined using subcutaneous inoculation of gallbladder carcinoma cells in Balb/c nude mice. RESULTS Compared with their paired normal gallbladder samples, the gallbladder carcinoma samples had decreased expression of miR-138 and increased expression of Bag-1. Overexpression of miR-138 inhibited the proliferation of gallbladder carcinoma cells. Bag-1 was defined as a novel target of miR-138. Both the inhibition of Bag-1 by miR-138 and the silencing of Bag-1 by siRNA led to alterations of apoptosis-related proteins such as Bcl-2 and Bax. Restoring expression of Bag-1 eliminates the effects of miR-138 on cell proliferation and apoptosis. Furthermore, overexpression of miR-138 markedly inhibited the growth of tumors in the gallbladder carcinoma xenograft model in nude mice. CONCLUSIONS Expression of miR-138 is frequently reduced in gallbladder carcinoma when compared to normal cells. Overexpression of miR-138 inhibited cell proliferation by directly suppressing the expression of Bag-1. These results suggest that miR-138 plays an important role in inhibiting the growth of gallbladder carcinoma.