Autophagy regulates tumorigenesis through selective degradation of cyclin D1

Abstract

H-rasval12 induces autophagy through multiple signaling pathways including Raf-1/ERK pathway and various ERK downstream molecules of autophagy have been reported We clarify that Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (BNIP3) is a downstream molecule of the Ras/Raf/ERK signaling pathway to induce autophagy in H-rasval12-related tumorigenesis BNIP3 is up-regulated by H-rasval12 at the transcriptional level and then competes with Beclin 1 for binding with Bcl-2 Expression of ectopic BNIP3 further enhanced autophagy and suppressed H-rasval12 induced tumorigenesis in mice through the inhibition of cell proliferation Consistently high expression of H-rasval12 BNIP3 and LC3-II was also detected in the human bladder cancer specimens indicating that Ras BNIP3 and autophagy are involved in tumorigenesis We demonstrate a homeostasis between BNIP3 mediated autophagy and H-rasval12-induced tumor formation Further analysis revealed that the cell cycle was arrested at G1 phase and the interaction among cyclin D1 LC3 and p62 (an adaptor protein) was increased when autophagy was induced It indicates that autophagy may participate in cell cycle regulation In hepatocelluar carcinoma (HCC) dysregulated expression of cyclin D1 and aberrant autophagy has been reported separately However the relationship between them has not been explored In this study we demonstrated that autophagy was inversely correlated with cyclin D1 expression in 152 paired HCC patient specimens HCC specimens with highly expression of cyclin D1 shows correlation with poor overall survival rate Furthermore induction of autophagy by amiodarone (antiarrhythmic drug) in Hep 3B cells cyclin D1 was recruited into autophagosomes demonstrated by immune-gold labeling of cyclin D1 after extraction of autophagosomes We further demonstrated that autophagy suppresses hepatoma Hep 3B cell proliferation and further analysis revealed that cell cycle was arrested at G1 phase The interaction between LC3 and cyclin D1 was increased after autophagy induction In addition ubiquitinated-cyclin D1 was also increased after autophagy induction and then is selectively degraded by autophagosome through binding with SQSTM1/p62 (an adaptor protein) Our in vivo study showed that amiodarone induced autophagy suppresses liver tumor formation in xenograft mouse and orthotopic rat model through decreasing cyclin D1 expression and inhibition of cell proliferation Altogether we reveal a novel mechanism by which ubiquitinated cyclin D1 was degraded by p62 mediated autophagic pathway and amiodarone is a promising drug for targeting cyclin D1 in liver cancer therapy

Date of Award	2014 Jan 21
Original language	English
Supervisor	Hsiao-Sheng Liu (Supervisor)