Growth factor regulation of autophagy and cell survival in the absence of apoptosis

Lum JJ, Bauer DE, Kong M, Harris MH, Li C, Lindsten T and Thompson CB
Source: Cell
Publication Date: (2005)
Issue: 120(2): 237-248
Research Area:
Immunotherapy / Hematology
Cells used in publication:
Bone marrow, mouse
Species: mouse
Tissue Origin: bone marrow
Nucleofector® I/II/2b
Primary bone marrow cells from Bax-/-Bak-/- mice were transfected with a single plasmid coding for both shRNA to ATG5 (a protein involved in autophagy) and for GFP. Thus, the transfected, i.e. knock-down cells, could be sorted by their GFP-fluorescence with FACS. The cells were also transfected with FITC-labeled siRNA duplexes, similarly enabling sorting of transfected cells by FACS.
In animals, cells are dependent on extracellular signals to prevent apoptosis. However, using growth factor-dependent cells from Bax/Bak-deficient mice, we demonstrate that apoptosis is not essential to limit cell autonomous survival. Following growth factor withdrawal, Bax(-/-)Bak(-/-) cells activate autophagy, undergo progressive atrophy, and ultimately succumb to death. These effects result from loss of the ability to take up sufficient nutrients to maintain cellular bioenergetics. Despite abundant extracellular nutrients, growth factor-deprived cells maintain ATP production from catabolism of intracellular substrates through autophagy. Autophagy is essential for maintaining cell survival following growth factor withdrawal and can sustain viability for several weeks. During this time, cells respond to growth factor readdition by rapid restoration of the ability to take up and metabolize glucose and by subsequent recovery of their original size and proliferative potential. Thus, growth factor signal transduction is required to direct the utilization of sufficient exogenous nutrients to maintain cell viability.