Taylor John M, Quilty Douglas, Banadyga Logan, Barry Michele
Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
J Biol Chem. 2006 Dec 22;281(51):39728-39. doi: 10.1074/jbc.M607465200. Epub 2006 Oct 30.
Vaccinia virus, the prototypic member of the orthopoxvirus genus, encodes the mitochondrial-localized protein F1L that functions to protect cells from apoptotic death and inhibits cytochrome c release. We previously showed that F1L interacts with the pro-apoptotic Bcl-2 family member Bak and inhibits activation of Bak following an apoptotic stimulus (Wasilenko, S. T., Banadyga, L., Bond, D., and Barry, M. (2005) J. Virol. 79, 14031-14043). In addition to Bak, the pro-apoptotic protein Bax is also capable of initiating cytochrome c release suggesting that vaccinia virus infection could also inhibit Bax activity. Here we show that F1L inhibits the activity of the pro-apoptotic protein Bax by inhibiting oligomerization and N-terminal activation of Bax. F1L expression also inhibited the subcellular redistribution of Bax to the mitochondria and the insertion of Bax into the outer mitochondrial membrane. The ability of F1L to inhibit Bax activation does not require Bak, because F1L expression inhibited cytochrome c release and Bax activation in Bak-deficient cells. No interaction between Bax and F1L was detected during infection, suggesting that F1L functions upstream of Bax activation. Notably, F1L was capable of interacting with the BH3-only protein BimL as shown by co-immunoprecipitation, and F1L expression inhibited apoptosis induced by BimL. These studies suggest that, in addition to interacting with the pro-apoptotic protein Bak, F1L also functions to indirectly inhibit the activation of Bax, likely by interfering with the pro-apoptotic activity of BH3-only proteins such as BimL.
痘苗病毒是正痘病毒属的原型成员，编码定位于线粒体的蛋白F1L，该蛋白的功能是保护细胞免于凋亡死亡并抑制细胞色素c的释放。我们之前的研究表明，F1L与促凋亡的Bcl-2家族成员Bak相互作用，并在凋亡刺激后抑制Bak的激活（Wasilenko, S. T., Banadyga, L., Bond, D., and Barry, M. (2005) J. Virol. 79, 14031-14043）。除了Bak之外，促凋亡蛋白Bax也能够引发细胞色素c的释放，这表明痘苗病毒感染也可能抑制Bax的活性。在此我们表明，F1L通过抑制Bax的寡聚化和N端激活来抑制促凋亡蛋白Bax的活性。F1L的表达还抑制了Bax向线粒体的亚细胞重新分布以及Bax插入线粒体外膜。F1L抑制Bax激活的能力并不需要Bak，因为F1L的表达在Bak缺陷型细胞中抑制了细胞色素c的释放和Bax的激活。在感染过程中未检测到Bax与F1L之间的相互作用，这表明F1L在Bax激活的上游发挥作用。值得注意的是，如免疫共沉淀所示，F1L能够与仅含BH3结构域的蛋白BimL相互作用，并且F1L的表达抑制了由BimL诱导的凋亡。这些研究表明，除了与促凋亡蛋白Bak相互作用之外，F1L还可能通过干扰仅含BH3结构域的蛋白（如BimL）的促凋亡活性来间接抑制Bax的激活。
