Silencing of Bcl-2 expression by small interfering RNA induces autophagic cell death in MCF-7 breast cancer cells

• Published in: Autophagy Vol. 4; no. 5; pp. 669 - 679
• Main Authors: Akar, Ugur, Chaves-Reyez, Arturo, Barria, Magaly, Tari, Ana, Sanguino, Angela, Kondo, Yasuko, Kondo, Seiji, Arun, Banu, Lopez-Berestein, Gabriel, Ozpolat, Bulent
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 01-07-2008
• Subjects: Autophagy - genetics; Autophagy - physiology; Binding; Biology; Bioscience; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Calcium; Cancer; Cell; Cell Line, Tumor; Cell Survival - genetics; Cycle; Female; Gene Expression Regulation, Neoplastic - genetics; Gene Silencing - physiology; Growth Inhibitors - physiology; Humans; Landes; Organogenesis; Proteins; Proto-Oncogene Mas; Proto-Oncogene Proteins c-bcl-2 - antagonists & inhibitors; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; Proto-Oncogene Proteins c-bcl-2 - genetics; RNA Interference - physiology; RNA, Small Interfering - physiology
• ISSN: 1554-8627; 1554-8635
• DOI: 10.4161/auto.6083

Apoptosis (programmed cell death type I) and autophagy (type II) are crucial mechanisms regulating cell death and homeostasis. The Bcl-2 proto-oncogene is overexpressed in 50-70% of breast cancers, potentially leading to resistance to chemotherapy, radiation and hormone therapy induced apoptosis. In this study, we investigated the role of Bcl-2 in autophagy in breast cancer cells. Silencing of Bcl-2 by siRNA in MCF-7 breast cancer cells downregulated Bcl-2 protein levels (>85%) and led to inhibition of cell growth (71%) colony formation (79%), and cell death (up to 55%) by autophagy but not apoptosis. Induction of autophagy was demonstrated by acridine orange staining, electron microscopy and an accumulation of GFP-LC3-II in preautopghagosomal and autophagosomal membranes in MCF-7 cells transfected with GFP-LC-3(GFP-ATG8). Silencing of Bcl-2 by siRNA also led to induction of LC-3-II, a hallmark of autophagy, ATG5 and Beclin-1 autophagy promoting proteins. Knockdown of ATG5 significantly inhibited Bcl-2 siRNA-induced LC3-II expression and the number of GFP-LC3-II-labeled autophagosome (punctuated pattern) positive cells and autophagic cell death (p