Bcl-2 Prevents Bax Oligomerization in the Mitochondrial Outer Membrane

• Published in: The Journal of biological chemistry 2001-05, Vol.276 (21), p.18361-18374
• Main Authors: Mikhailov, Valery, Mikhailova, Margarita, Pulkrabek, Donna J., Dong, Zheng, Venkatachalam, Manjeri A., Saikumar, Pothana
• Format: Article
• Language: English
• Subjects: Animals; bcl-2-Associated X Protein; Cell Line; Dimerization; Intracellular Membranes - chemistry; Intracellular Membranes - metabolism; Mitochondria - chemistry; Mitochondria - metabolism; Proto-Oncogene Proteins - chemistry; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - chemistry; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rats
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M100655200

ATP depletion results in Bax translocation from cytosol to mitochondria and release of cytochrome c from mitochondria into cytosol in cultured kidney cells. Overexpression of Bcl-2 prevents cytochrome c release, without ameliorating ATP depletion or Bax translocation, with little or no association between Bcl-2 and Bax as demonstrated by immunoprecipitation (Saikumar, P., Dong, Z., Patel, Y., Hall, K., Hopfer, U., Weinberg, J. M., and Venkatachalam, M. A. (1998) Oncogene 17, 3401–3415). Now we show that translocated Bax forms homo-oligomeric structures, stabilized as chemical adducts by bifunctional cross-linkers in ATP-depleted wild type cells, but remains monomeric in Bcl-2-overexpressing cells. The protective effects of Bcl-2 did not require Bcl-2/Bax association, at least to a degree of proximity or affinity that was stable to conditions of immunoprecipitation or adduct formation by eight cross-linkers of diverse spacer lengths and chemical reactivities. On the other hand, nonionic detergents readily induced homodimers and heterodimers of Bax and Bcl-2. Moreover, associations between translocated Bax and the voltage-dependent anion channel protein or the adenine nucleotide translocator protein could not be demonstrated by immunoprecipitation of Bax, or by using bifunctional cross-linkers. Our data suggest that the in vivo actions of Bax are at least in part dependent on the formation of homo-oligomers without requiring associations with other molecules and that Bcl-2 cytoprotection involves mechanisms that prevent Bax oligomerization.