Polyphyllin I induces mitophagic and apoptotic cell death in human breast cancer cells by increasing mitochondrial PINK1 levels

Abstract

// Guo-Bing Li 1, 2, * , Ruo-Qiu Fu 1, * , Han-Ming Shen 3 , Jing Zhou 1 , Xiao-Ye Hu 1 , Yan-Xia Liu 1 , Yu-Nong Li 1 , Hong-Wei Zhang 1 , Xin Liu 1 , Yan-Hao Zhang 1 , Cheng Huang 4 , Rong Zhang 2 , Ning Gao 1 1 Department of Pharmacognosy, College of Pharmacy, 3rd Military Medical University, Chongqing, China 2 Department of Pharmacy, The Second Affiliated Hospital of Third Military Medical University, Chongqing, China 3 Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Republic of Singapore 4 Drug Discovery Lab, School of Pharmacy, Shanghai University of Traditional Chinese Medicine, Shanghai, China * These authors have contributed equally to this work Correspondence to: Ning Gao, email: gaoning59@163.com Rong Zhang, email: xqpharmacylab@126.com Keywords: polyphyllin I, DRP1, mitochondrial fission, mitophagy, PINK1 Received: May 17, 2016      Accepted: December 12, 2016      Published: January 02, 2017 ABSTRACT The molecular mechanisms underlying the anti-breast cancer effects of polyphyllin I, a natural compound extracted from Paris polyphylla rhizomes, are not fully understood. In the present study, we found that polyphyllin I induces mitochondrial translocation of DRP1 by dephosphorylating DRP1 at Ser637, leading to mitochondrial fission, cytochrome c release from mitochondria into the cytosol and, ultimately apoptosis. Polyphyllin I also increased the stabilization of full-length PINK1 at the mitochondrial surface, leading to the recruitment of PARK2, P62, ubiquitin, and LC3B-II to mitochondria and culminating in mitophagy. PINK1 knockdown markedly suppressed polyphyllin I-induced mitophagy and enhanced polyphyllin I-induced, DRP1-dependent mitochondrial fission and apoptosis. Furthermore, suppression of DRP1 by mdivi-1 or shRNA inhibited PINK1 knockdown/polyphyllin I-induced mitochondrial fragmentation and apoptosis, suggesting that PINK1 depletion leads to excessive fission and, subsequently, mitochondrial fragmentation. An in vivo study confirmed that polyphyllin I greatly inhibited tumor growth and induced apoptosis in MDA-MB-231 xenografts, and these effects were enhanced by PINK1 knockdown. These data describe the mechanism by which PINK1 contributes to polyphyllin I-induced mitophagy and apoptosis and suggest that polyphyllin I may be an effective drug for breast cancer treatment.