BimL directly neutralizes Bcl-xL to promote Bax activation during UV-induced apoptosis.
Bcl-2-interacting mediator of cell death (Bim) has been considered to initiate intrinsic apoptotic pathway through Bax activation. Previous studies indicated that BimL was involved in UV-induced apoptosis, but it remains unclear whether Bim activates Bax by directly engaging it or by releasing it from pro-survival relatives such as Bcl-xL. In this study, we attempt to determine the interactions between BimL and Bax/Bcl-xL during Ultraviolet (UV)-induced apoptosis. BimL activation appeared to be an important event in our experiments, as demonstrated by the significant inhibition of cell death, caspase-3 activity, and Bax translocation in cells with knockdown of endogenous BimL by RNAi approach. Both fluorescence resonance energy transfer (FRET) and Co-immunoprecipitation (CO-IP) assays indicated that Bcl-xL directly bound to Bax to inhibit its activation, while BimL directly neutralized Bcl-xL, followed by Bax release and activation upon UV irradiation. Not detected in our experiment was the interaction between BimL and Bax either using FRET approach in living cells or endogenous CO-IP assay. Thus, our findings provide strong evidence in living cells for the first time that BimL initiates apoptosis by abrogating Bcl-xL and promoting Bax activation under UV irradiation.
Wang
Xianwang
X
MOE Key Laboratory of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, China.
Xing
Da
D
Liu
Lei
L
Chen
Wei R
WR
D000818:Animals; D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects*; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D000072224:Bcl-2-Like Protein 11; D019556:COS Cells; D002522:Chlorocebus aethiops; D017931:DNA Primers / Q000235:genetics; D031541:Fluorescence Resonance Energy Transfer; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008954:Models, Biological; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D017931:DNA Primers; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein