Molecular cloning and characterization of six novel isoforms of human Bim, a member of the proapoptotic Bcl-2 family.
Bim protein is one of the BH3-only proteins, members of the Bcl-2 family that have only one of the Bcl-2 homology regions, BH3. BH3-only proteins are essential initiators of apoptotic cell death. Thus far, three isoforms of Bim have been reported, i.e. Bim(EL), Bim(L) and Bim(S). Here we report the cloning and characterization of six novel isoforms of human Bim, designated as Bimalpha1, alpha2, and beta1-beta4, which are generated by alternative splicing. Unlike the three known isoforms, none of these novel isoforms contained a C-terminal hydrophobic region. Among the novel isoforms, only Bimalpha1 and alpha2 contained a BH3 domain and were proapoptotic, although less potent than the classical isoforms. These two isoforms localized, at least in part, in mitochondria when transiently expressed in HeLa cells as a green fluorescent protein-fused form. These results suggest that the BH3 domain is necessary for induction of apoptosis and mitochondrial localization but not sufficient for the full proapoptotic activity. While the classical isoforms were always predominantly expressed in transformed cells, expression profiles of bim isoforms were highly variable among normal tissues at least in humans, suggesting a tissue-specific transcriptional regulation of bim.
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Department of Genetics, National Children's Medical Research Center, 3-35-31 Taishido, Setagayaku, 154-8509, Tokyo, Japan.
Miyashita
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T
Shikama
Y
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Tadokoro
K
K
Yamada
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M
D000595:Amino Acid Sequence; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D002460:Cell Line; D002461:Cell Line, Transformed; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008156:Luciferases / Q000378:metabolism; D008565:Membrane Proteins; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D012313:RNA / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions; D013997:Time Factors; D014018:Tissue Distribution; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D012313:RNA; D008156:Luciferases