Role of Autophagy as a Survival Mechanism for Hypoxic Cells in Tumors.
Enhanced autophagy has been observed in hypoxic regions of solid tumors. Here we address the hypothesis that autophagy is required for survival of hypoxic cells. We evaluated sensitivity to hypoxia of three human tumor cell lines (MCF7, PC3, and LNCaP) and their autophagy-deficient variants with shRNA knockdown of the genes ATG7 and BECLIN1. Hypoxia-induced cell death was more rapid for autophagy-deficient cells and was increased in the presence of the proton pump inhibitor pantoprazole that inhibits autophagy. Autophagy-deficient cells had a lower rate of oxygen consumption than wild-type cells. In xenografts derived from the three cell lines, autophagy (as determined by increased LC3 and reduced p62/SQSTM1) colocalized with hypoxic regions (identified by EF5). Xenografts derived from autophagy-deficient cells grew more slowly than wild-type tumors. Both LC3 expression and hypoxia were decreased in xenografts generated from single-knockdown cells and absent in double-knockdown tumors. Our results are consistent with the hypothesis that autophagy facilitates the survival of hypoxic cells, although reduced oxygen consumption of autophagy-deficient cells may contribute to lack of hypoxia in tumors derived from them. Because hypoxia is associated with resistance to anticancer therapy, inhibition of autophagy has potential to enhance the effectiveness of cancer treatment.
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada. Electronic address: susie.tan@uhnres.utoronto.ca.
Qian
Q
Tan
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada.
Marina
M
Wang
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada.
Man
M
Yu
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada.
Junyan
J
Zhang
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada; Division of Medical Oncology and Hematology, Princess Margaret Hospital and University Health Network, University of Toronto, Toronto, ON, Canada.
Robert G
RG
Bristow
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada.
Richard P
RP
Hill
Department of Medical Biophysics, University health Network, University of Toronto, Toronto, ON, Canada; Division of Medical Oncology and Hematology, Princess Margaret Hospital and University Health Network, University of Toronto, Toronto, ON, Canada. Electronic address: ian.tannock@uhn.ca.
Ian F
IF
Tannock
D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D000818:Animals; D001343:Autophagy / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D005260:Female; D006801:Humans; D061986:MCF-7 Cells; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000473:pathology*; D010101:Oxygen Consumption / Q000502:physiology*; D000077402:Pantoprazole; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D000071456:Sequestosome-1 Protein / Q000096:biosynthesis; D014183:Transplantation, Heterologous
D053799:2-Pyridinylmethylsulfinylbenzimidazoles; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D000071456:Sequestosome-1 Protein; C101343:Sqstm1 protein, mouse; D000077402:Pantoprazole