Endogenous association of Bim BH3-only protein with Mcl-1, Bcl-xL and Bcl-2 on mitochondria in human B cells.
Bim is an essential regulator of lymphoid system homeostasis and appears essential for B cell apoptosis induction. The mechanism by which Bim isoforms are held in an inactive form remains poorly documented in normal B cells. In the current study, we demonstrated that in normal tonsil B cells the three major Bim isoforms are strongly associated with the anti-apoptotic Bcl-2 family members Mcl-1, Bcl-2 and Bcl-x(L). On the other hand, only a weak association of BimEL and L with the dynein LC8 chain has been found. In addition, there is no free Bim in normal B cells. Moreover, subcellular fractionation demonstrated that Bim and the anti-apoptotic counterparts are localized preferentially in the mitochondria-rich fraction. The fact that most Bim was found in this fraction supports the hypothesis that it is sequestered by anti-apoptotic molecules in mitochondria where its pro-apoptotic activity is controlled. Of interest, BimS is essentially complexed to Mcl-1 and the Mcl-1/Bim complex is the most abundant among the three types of complexes. This supports the idea that this complex is critical for the control of B cell death. In conclusion, these results favor a model in which Bim release from anti-apoptotic proteins is a critical event for initiation of apoptosis.
Gomez-Bougie
Patricia
P
INSERM, UMR601, Département de Recherche en Cancérologie, Equipe 5 labélisée L N C, Institut de Biologie, Nantes, France.
Bataille
Régis
R
Amiot
Martine
M
D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D008928:Mitochondria / Q000276:immunology / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000276:immunology / Q000378:metabolism*; D014066:Palatine Tonsil / Q000166:cytology; D020033:Protein Isoforms / Q000276:immunology / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000276:immunology / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000276:immunology / Q000378:metabolism*; D051020:bcl-X Protein
D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein