Characterization of Bax-sigma, a cell death-inducing isoform of Bax.
The Ced-9/Bcl-like family of genes codes for proteins that have antiapoptotic and proapoptotic activity. Several Bax isoproteins have been detected by 2-D gel electrophoresis, and a novel human member, designated as Bax-sigma, has been identified and cloned from human cancer promyelocytic cells. Bax-sigma contains BH-3, BH-1, and BH-2 domains, putative alpha-5 and alpha-6 helices, and the carboxy-terminal hydrophobic transmembrane domain but lacks amino acids 159 to 171 compared to Bax-alpha. mRNA expression analysis by reverse transcription-polymerase chain reaction and RNase protection assays have revealed that Bax-sigma is expressed in a variety of human cancer cell lines and normal tissues. To investigate the potential role of Bax-sigma in apoptosis, first its effects were compared to those of Bax-alpha by transient expression in human B lymphoma Namalwa cells. Both Bax-sigma and Bax-alpha promoted apoptosis, as detected by DNA fragmentation and morphological analysis by electron microscopy. The apoptosis induced by Bax-sigma and Bax-alpha was correlated with their expression, cytochrome c release, and caspase activation. In a yeast two-hybrid system, Bax-sigma interacted with several Ced-9/Bcl family members but had no affinity for the human Egl-1 homologs Bik and Bad and the Ced-4 homolog Apaf-1. In human cells, Bax-sigma function was counteracted by Bcl-xL overexpression, and co-immunoprecipitation experiments indicated that Bax-sigma was associated with Bcl-xL. Furthermore, Bax-sigma overexpression increased cell death induced by various concentrations of genotoxic agents with the most pronounced effect occurring at low camptothecin and vinblastine dose levels. Our results suggest that Bax-sigma, a novel variant of Bax, encodes a protein with a proapoptotic effect and mode of action similar to those of Bax-alpha.
Schmitt
E
E
Research Centre of the University of Montreal Hospital Centre, Notre Dame Hospital, Montreal, Quebec, H2L 4M1, Canada.
Paquet
C
C
Beauchemin
M
M
Dever-Bertrand
J
J
Bertrand
R
R
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D017209:Apoptosis; D001483:Base Sequence; D003001:Cloning, Molecular; D053938:DNA Fragmentation; D005260:Female; D019254:Genes, bcl-2; D014644:Genetic Variation; D018922:HL-60 Cells; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein