BMP4 promotes hepatocellular carcinoma proliferation by autophagy activation through JNK1-mediated Bcl-2 phosphorylation

Background Autophagy is a conserved catabolic process with complicated roles in tumor development. Bone morphogenetic protein 4 (BMP4), a member of the transforming growth factor (TGF-β) family of regulatory proteins, plays a crucial role in human malignancies. However, whether BMP4 contributes to the regulation of autophagy in hepatocellular carcinoma (HCC) progression remains elusive. Methods Functional analysis of BMP4 on HCC proliferation and autophagy was performed both in vitro and in vivo in HepG2 and HCCLM3 cells. Autophagic activity was estimated by Western blot for autophagic marker proteins and by transmission electron microscopy (TEM). Transfection of mRFP-GFP-LC3 adenovirus was applied to observe autophagic flux and high content screening was used for quantification. The signaling pathway of BMP4-regulated HCC proliferation and autophagy was investigated by Western blot. Results BMP4 treatment promoted HCC cells proliferation and induced autophagy. The in vivo xenograft model supported that BMP4 overexpression promoted the growth of HCC cells and autophagy induction while BMP4 knockdown exerted the opposite effect. 3-MA pre-treatment or knockdown of Beclin-1 (BECN1) blocked HCC autophagy by decreasing the expression of LC3-II and subsequently attenuated BMP4-induced autophagy and cells proliferation enhanced by BMP4 in vitro and in vivo. Mechanistic study revealed that the induction of autophagy by BMP4 was mediated through activating the JNK1/Bcl2 pathway. Furthermore, the JNK1 inhibitor and knockdown of JNK1 could attenuate autophagy induced by BMP4 and eliminated BMP4-promoted HCC cells growth. Conclusions BMP4 promoted HCC proliferation by autophagy activation through JNK1/Bcl-2 signaling.