title: Silencing of Bcl-2 expression by small interfering RNA induces autophagic cell death in MCF-7 breast cancer cells.
abstract: 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. Here, 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 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, the number of GFP-LC3-II-labeled autophagosome positive cells and autophagic cell death (p < 0.05). Furthermore, doxorubicin at a high dose (IC(95), 1 microM) induced apoptosis but at a low dose (IC(50), 0.07 microM) induced only autophagy and Beclin-1 expression. When combined with Bcl-2 siRNA, doxorubicin (IC(50)) enhanced autophagy as indicated by the increased number cells with GFP-LC3-II-stained autophagosomes (punctuated pattern positive). These results provided the first evidence that targeted silencing of Bcl-2 induces autophagic cell death in MCF-7 breast cancer cells and that Bcl-2 siRNA may be used as a therapeutic strategy alone or in combination with chemotherapy in breast cancer cells that overexpress Bcl-2.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Ugur
authors.initials: U
authors.lastname: Akar
authors.forename: Arturo
authors.initials: A
authors.lastname: Chaves-Reyez
authors.forename: Magaly
authors.initials: M
authors.lastname: Barria
authors.forename: Ana
authors.initials: A
authors.lastname: Tari
authors.forename: Angela
authors.initials: A
authors.lastname: Sanguino
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Kondo
authors.forename: Seiji
authors.initials: S
authors.lastname: Kondo
authors.forename: Banu
authors.initials: B
authors.lastname: Arun
authors.forename: Gabriel
authors.initials: G
authors.lastname: Lopez-Berestein
authors.forename: Bulent
authors.initials: B
authors.lastname: Ozpolat
mesh_terms: D001343:Autophagy / Q000235:genetics* / Q000502:physiology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D020868:Gene Silencing / Q000502:physiology*; D006131:Growth Inhibitors / Q000502:physiology; D006801:Humans; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics*; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering / Q000502:physiology*
chemical_list: D006131:Growth Inhibitors; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering