title: MEK kinase 1 induces mitochondrial permeability transition leading to apoptosis independent of cytochrome c release.
abstract: Induction of apoptosis often converges on the mitochondria to induce permeability transition and release of apoptotic proteins into the cytoplasm resulting in the biochemical and morphological alteration of apoptosis. Activation of a serine threonine kinase MEK kinase 1 (MEKK1) is involved in the induction of apoptosis. Expression of a kinase-inactive MEKK1 blocks genotoxin-induced apoptosis. Upon apoptotic stimulation, MEKK1 is cleaved into a 91-kDa kinase fragment that further induces an apoptotic response. Mutation of a consensus caspase 3 site in MEKK1 prevents its induction of apoptosis. The mechanism of MEKK1-induced apoptosis downstream of its cleavage, however, is unknown. Herein we demonstrate that full-length and cleaved MEKK1 leads to permeability transition in the mitochondria. This permeability transition occurs through opening of the permeability transition (PT) pore. Inhibiting PT pore opening and reactive oxygen species production effectively reduced MEKK1-induced apoptosis. Overexpression of MEKK1, however, failed to release cytochrome c from the mitochondria or activate caspase 9. Since Bcl2 regulates changes in mitochondria and blocks MEKK1-induced apoptosis, we determined that Bcl2 blocks MEKK1-induced apoptosis when targeted to the mitochondria. This occurs downstream of MEKK1 cleavage, since Bcl2 fails to block cleavage of MEKK1. In mouse embryonic fibroblast cells lacking caspase 3, the cleaved but not full-length MEKK1 induces apoptosis and permeability transition in the mitochondria. Overall, this suggests that cleaved MEKK1 leads to permeability transition contributing to MEKK1-induced apoptosis independent of cytochrome c release from the mitochondria.
authors.affiliation: Manitoba Institute of Cell Biology, Winnipeg, Manitoba R3E 0V9, Canada. gibsonsb@cc.umanitoba.ca
authors.forename: Erika M
authors.initials: EM
authors.lastname: Gibson
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Henson
authors.forename: Jacylyn
authors.initials: J
authors.lastname: Villanueva
authors.forename: Spencer B
authors.initials: SB
authors.lastname: Gibson
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000235:genetics; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D003574:Cytochrome c Group; D018076:DNA, Complementary; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases