Downregulated MEG3 activates autophagy and increases cell proliferation in bladder cancer

Maternally Expressed Gene 3 (MEG3) is an imprinted gene that encodes a long non-coding RNA (lncRNA) associated with tumorigenesis. Autophagy is activated in cancer cells and contributes to tumor cell survival. However, little is known about whether MEG3 regulates bladder cancer development by controlling autophagy. In the study, we found that MEG3 levels were significantly reduced in bladder cancer tissues compared with normal controls, and autophagy activity was increased in bladder cancer tissues. A significant negative correlation was observed between MEG3 levels and LC3-II (autophagy marker) levels in vivo. We further demonstrated that MEG3 markedly suppressed autophagy activation, whereas MEG3 knockdown activated autophagy in human bladder cancer cell lines. Downregulated expression of MEG3 inhibited cell apoptosis, whereas autophagy inhibition increased MEG3-knockdown cell apoptosis. MEG3 knockdown also increased cell proliferation. More importantly, autophagy inhibition abrogated MEG3 knockdown-induced cell proliferation. These data demonstrated that downregulated MEG3 activates autophagy and increases cell proliferation in bladder cancer.