Apaf-1XL is an inactive isoform compared with Apaf-1L.
Apaf-1 plays a crucial role in the cytochrome c/dATP-dependent activation of caspase-9 and -3. We found that the human myeloid leukemic K562 cells were more resistant to cytochrome c-induced activation of caspase-9 and -3 in a cell-free system compared with the human T-lymphoblastic subclone CEM/VLB(100) cells. Apaf-1 cDNA sequencing revealed an additional insert of 11 aa between the CARD and CED-4 (ATPase) domains in K562 cells, which was identical to the sequence of Apaf-1XL. Immunoprecipitation of Apaf-1 with caspase-9 after a cell-free reaction demonstrated that Apaf-1XL in the K562 cell line showed a lower binding ability to caspase-9 compared with Apaf-1L protein. The resistance of K562 cells to cytochrome c-dependent apoptosis may be partly due to this Apaf-1XL form. These results suggest that the additional insert between CARD and CED-4 domains might affect Apaf-1 recruitment of caspase-9 during apoptosis.
Department of Haematology/Oncology, St. Bartholomew's and Royal London School of Medicine and Dentistry, Turner Street, London, E1 2AD, United Kingdom.
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Fu
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Kelsey
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Newland
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Jia
D000251:Adenosine Triphosphatases / Q000378:metabolism; D053477:Apoptotic Protease-Activating Factor 1; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D018076:DNA, Complementary; D004789:Enzyme Activation; D006801:Humans; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D003574:Cytochrome c Group; D018076:DNA, Complementary; D020033:Protein Isoforms; D011506:Proteins; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D000251:Adenosine Triphosphatases