title: Two distinct steps of Bak regulation during apoptotic stress signaling: different roles of MEKK1 and JNK1.
abstract: Stress-activated protein (SAP) kinases and the mitochondrial pro-apoptotic Bcl-2 protein Bak are important regulators of apoptosis. Reduced expression of Bak increases cellular resistance to the anticancer agent cisplatin, and we report here that mouse embryo fibroblasts deficient in the SAP kinase jnk1 are highly resistant to apoptosis induced by cisplatin. When human melanoma cells were treated with cisplatin, Bak function was found to be regulated in two distinct steps by two SAP kinases, MEKK1 and JNK1. The first of these steps involves MEKK1-controlled conformational activation of Bak. The second step leads to formation of 80-170 kDa Bak complexes correlating with apoptosis, and is controlled by JNK1. Inhibition of MEKK1 blocked the initial Bak conformational activation but did not block JNK1 activation, and deficiency in, or inhibition of, JNK1 did not prevent conformational activation of Bak. Furthermore, inducible expression of a constitutively active form of MEKK1 led to Bak conformational activation, but not to 80-170 kDa complexes. Consequently, apoptosis was delayed unless JNK was exogenously stimulated, indicating that Bak conformational activation is not necessarily an apoptotic marker. The two-step regulation of Bak revealed here may be important for tight control of mitochondrial factor release and apoptosis.
authors.affiliation: Department Oncology-Pathology, Cancer Center Karolinska, Karolinska Institute R8:03, S-171 76 Stockholm, Sweden.
authors.forename: Linda Strandberg
authors.initials: LS
authors.lastname: Ihrlund
authors.forename: Emma
authors.initials: E
authors.lastname: Hernlund
authors.forename: Kristina
authors.initials: K
authors.lastname: Viktorsson
authors.forename: Theocharis
authors.initials: T
authors.lastname: Panaretakis
authors.forename: Gabor
authors.initials: G
authors.lastname: Barna
authors.forename: Kanaga
authors.initials: K
authors.lastname: Sabapathy
authors.forename: Stig
authors.initials: S
authors.lastname: Linder
authors.forename: Maria C
authors.initials: MC
authors.lastname: Shoshan
mesh_terms: D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000172:deficiency / Q000235:genetics; D051023:BH3 Interacting Domain Death Agonist Protein / Q000172:deficiency / Q000235:genetics; D000072224:Bcl-2-Like Protein 11; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics; D051379:Mice; D048055:Mitogen-Activated Protein Kinase 8 / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000502:physiology; D008954:Models, Biological; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013012:Sorbitol / Q000494:pharmacology; D014162:Transfection; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000873:Anthracenes; D051017:Apoptosis Regulatory Proteins; C494772:BAK1 protein, human; C000606775:BCL2L11 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C494815:Bid protein, mouse; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D050998:bcl-2 Homologous Antagonist-Killer Protein; C432165:pyrazolanthrone; D013012:Sorbitol; D045304:Cytochromes c; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D048051:p38 Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D002945:Cisplatin