Autophagy provides nutrients but can lead to Chop-dependent induction of Bim to sensitize growth factor-deprived cells to apoptosis.
Tissue homeostasis is controlled by the availability of growth factors, which sustain exogenous nutrient uptake and prevent apoptosis. Although autophagy can provide an alternate intracellular nutrient source to support essential basal metabolism of apoptosis-resistant growth factor-withdrawn cells, antiapoptotic Bcl-2 family proteins can suppress autophagy in some settings. Thus, the role of autophagy and interactions between autophagy and apoptosis in growth factor-withdrawn cells expressing Bcl-2 or Bcl-xL were unclear. Here we show autophagy was rapidly induced in hematopoietic cells upon growth factor withdrawal regardless of Bcl-2 or Bcl-xL expression and led to increased mitochondrial lipid oxidation. Deficiency in autophagy-essential gene expression, however, did not lead to metabolic catastrophe and rapid death of growth factor-deprived cells. Rather, inhibition of autophagy enhanced survival of cells with moderate Bcl-2 expression for greater than 1 wk, indicating that autophagy promoted cell death in this time frame. Cell death was not autophagic, but apoptotic, and relied on Chop-dependent induction of the proapoptotic Bcl-2 family protein Bim. Therefore, although ultimately important, autophagy-derived nutrients appear initially nonessential after growth factor withdrawal. Instead, autophagy promotes tissue homeostasis by sensitizing cells to apoptosis to ensure only the most apoptosis-resistant cells survive long-term using autophagy-derived nutrients when growth factor deprived.
Altman
Brian J
BJ
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
Wofford
Jessica A
JA
Zhao
Yuxing
Y
Coloff
Jonathan L
JL
Ferguson
Emily C
EC
Wieman
Heather L
HL
Day
Amanda E
AE
Ilkayeva
Olga
O
Rathmell
Jeffrey C
JC
D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D001343:Autophagy; D000072224:Bcl-2-Like Protein 11; D005227:Fatty Acids / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051381:Rats; D051742:Transcription Factor CHOP / Q000378:metabolism*; D015854:Up-Regulation; D051020:bcl-X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C000606778:Bcl2l11 protein, rat; D005227:Fatty Acids; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D051020:bcl-X Protein; D051742:Transcription Factor CHOP; D005947:Glucose