BimL directly neutralizes Bcl-xL to promote Bax activation during UV-induced apoptosis

Wang, Xianwang; Xing, Da; Liu, Lei; Chen, Wei R.

doi:10.1016/j.febslet.2009.04.045

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Volume 583, Issue 12 , Pages 1873-1879, 18 June 2009

BimL directly neutralizes Bcl-xL to promote Bax activation during UV-induced apoptosis

Edited by Vladimir Skulachev

MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, China

Received 9 March 2009; received in revised form 28 April 2009; accepted 30 April 2009. published online 08 May 2009.

Abstract

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.

Structured summary

MINT-7034091: BIML (uniprotkb:O43521) physically interacts (MI:0218) with Bcl2-Xl (uniprotkb:Q92934) by anti bait coimmunoprecipitation (MI:0006)

MINT-7034079: Bcl2-Xl (uniprotkb:Q92934) physically interacts (MI:0218) with BAX (uniprotkb:Q07812) and BIML (uniprotkb:O43521) by anti bait coimmunoprecipitation (MI:0006)

MINT-7034069: BAX (uniprotkb:Q07812) physically interacts (MI:0218) with BIML (uniprotkb:O43521) by anti bait coimmunoprecipitation (MI:0006)

MINT-7034114: BIML (uniprotkb:O43521) and BAX (uniprotkb:Q07812) physically interact (MI:0218) by fluorescent resonance energy transfer (MI:0055)

Abbreviations: LCSM, laser confocal scanning microscopy, FRET, fluorescence resonance energy transfer, Bim, Bcl-2-interacting mediator of cell death, JNK, c-Jun N-terminal kinase, UV, Ultraviolet, CO-IP, Co-immunoprecipitation, RNAi, RNA interference, shRNA, short hairpin RNA