ARD1, which is the catalytic subunit of the N-acetyltransferase complex NatA, has been implicated in promoting apoptosis, suggesting that protein acetylation may serve a regulatory role in this form of cell death. Technical limitations in detecting protein N-acetylation have hampered the investigation of this modification. Yi et al. developed a biochemical assay to detect N-acetylated proteins. Knockdown of ARD1 sensitized cells to apoptosis in response to DNA-damaging agents but not death induced by activation of death receptors. Using the subtiligase-based assay, which attaches biotin to nonacetylated free N termini of proteins, a decrease in the abundance of N-acetylated caspase 2 and other proteins, based on immunoblotting and mass spectrometry, was detected after ARD1 knockdown. Altering metabolism by knocking down enzymes involved in acetyl-CoA synthesis also resulted in a decrease in N-acetylation of caspase 2. An N-acetylation–deficient mutant of caspase 2 (A3P) exhibited a decrease in N-acetylation and failed to interact with RAIDD, an adaptor of the caspase activation complex. Because the antiapoptotic protein Bcl-xL alters metabolism, Yi et al. investigated the effect of overexpression and genetic knockout on N-acetylation of proteins implicated in apoptosis (caspases 2, 9, and 3, and the proapoptotic protein Bax, which interacts with Bcl-xL) and found that overexpression of Bcl-xL reduced N-acetylation of these proteins, whereas genetic knockout increased their N-acetylation. The reduction in N-acetylation in Bcl-xL–overexpressing cells was reversed by addition of acetyl-CoA–generating metabolites, and these metabolites increased the sensitivity of the Bcl-xL–overexpressing cells to caspase activation and apoptosis in response to DNA damage with doxorubicin. Global metabolic profiling using two complementary methods revealed that acetyl-CoA was decreased in Bcl-xL–expressing cells, whereas acetyl-CoA was increased in genetic knockout cells. Glucose labeling experiments suggested that Bcl-xL overexpression altered glucose metabolism such that glucose-derived citrate, a precursor of acetyl-CoA, was reduced. These data have implications for understanding how metabolic changes can promote tumorigenesis and suggest that Bcl-xL has dual roles in promoting cell survival, by inhibiting Bax-mediated mitochondrial permeabilization and by altering metabolism to reduce protein N-acetylation.
C. H. Yi, H. Pan, J. Seebacher, I.-H. Jang, S. G Hyberts, G. J. Heffron, M. G. Vander Heiden, R. Yang, F. Li, J. W. Locasale, H. Sharfi, B. Zhai, R. Rodriguez-Mias, H. Luithardt, L. C. Cantley, G. Q Daley, J. M. Asara, S. P. Gygi, G. Wagner, C.-F. Liu, J. Yuan, Metabolic regulation of protein N-alpha-acetylation by Bcl-xL promotes cell survival. Cell 146, 607–620 (2011). [Online Journal]