Induction of Apoptosis by a Novel Bcl-2 Protein, Bak-like without a BH3 Domain

ABSTRACT

OBJECTIVE: In a variety of physiologic settings, cells are eliminated by apoptosis, a genetically encoded process of cellular suicide. Bak, a member of the Bcl-2 protein family, accelerates apoptosis by an unknown mechanism. Here, we describe the identification and characterization of a complementary DNA that encodes a previously unknown Bcl-2 homologue designated Bak-like. METHODS: We identified a splicing variant of Bak with a lacked BH3 domain from human full-length cDNA bank. The expression of Bak-like was examined by northern blot analysis and polymerase chain reaction. To investigate whether Bak-like might arise from alternative splicing of mRNA of Bak, Southern blot analysis was executed. Apoptosis in transfected HeLa cells was analyzed by direct counting of viable cells. We examined the location of Bak-like in individual living cells by using EGFP fusion constructs and confocal microscope. RESULTS: Bak-like cDNA coded a protein consisting of 101 amono acid, and conserved BH1 and BH2 domains like Bak but not BH3 domain. Bak-like mRNA was about 2.4kb similar to bak. Bak-like was assumed to be an alternative splicing variant of Bak and to concern with promotion of apoptosis. GFP-bak-like markedly changed its intracellular distribution, relocating within cells during apoptosis from a diffuse to a punctate pattern. CONCLUSION: Our results define a novel splicing form of the bak gene and demonstrate that this variant without a conserved BH3 domain appears to contain the BH1 and BH2 domains and the transmembrane sequence for apoptosis induction by channel-forming Bcl-2 proteins. Like Bak, Bak-like gene product primarily enhanced apoptotic cell death following an appropriate stimulus.