Bcl-xES, a BH4- and BH2-containing antiapoptotic protein, delays Bax oligomer formation and binds Apaf-1, blocking procaspase-9 activation.
Bcl-2 family members either negatively or positively regulate the apoptotic threshold of cells. Bcl-xES (extra short), a novel Bcl-x member, possesses a unique combination of BH4 and BH2 domains as well as a COOH-terminal hydrophobic transmembrane anchor domain. Bcl-xES contains sequences of hydrophobic alpha-6 helices but lacks sequences of alpha-5 helices, suggesting that it does not have pore channel-forming activity but functions uniquely as a trapping protein. mRNA expression analysis by reverse transcriptase-polymerase chain reaction and RNase protection assay reveal that Bcl-xES is expressed in a variety of human cancer cell lines and human tumors, including bone marrow from patients with acute lymphoblastic leukemia. Bcl-xES expression is much less pronounced in some specimens of normal human tissues, including the breast, ovary, testis and lung. Stable, transfected human B lymphoma Namalwa variant cells expressing Bcl-xES were derived to investigate its role in apoptosis. Bcl-xES had a preventive effect on cell death induced by tumor necrosis factor-alpha and various concentrations of anticancer drugs, including camptothecin, etoposide and cisplatin. Its protective action on cell death was correlated with the inhibition of mitochondrial cytochrome c release and caspase activation. In a yeast two-hybrid system, Bcl-xES interacted with most Bcl-2 family members, including those containing only a BH3 domain, and with the Ced-4 homolog Apaf-1. Co-immunoprecipitation and gel filtration chromatography experiments suggest that Bcl-xES delays drug-induced apoptosis by disturbing the formation of Bax oligomers and preventing cytochrome c release, but also by interacting with Apaf-1 and inhibiting procaspase-9 activation, thus averting the apoptogenic proteolytic caspase cascade and cell death.
Schmitt
Estelle
E
Centre de recherche, Centre hospitalier de l' Université of Montréal (CHUM), Hôpital Notre-Dame and Institut du cancer de Montréal, Montreal, Quebec, Canada.
Paquet
Claudie
C
Beauchemin
Myriam
M
Bertrand
Richard
R
D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D001483:Base Sequence; D002166:Camptothecin / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D059004:Topoisomerase I Inhibitors; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D004792:Enzyme Precursors; D011506:Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D059004:Topoisomerase I Inhibitors; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D020169:Caspases; D002166:Camptothecin