title: Inhibition of caspase-9 through phosphorylation at Thr 125 by ERK MAPK.
abstract: Many pro-apoptotic signals activate caspase-9, an initiator protease that activates caspase-3 and downstream caspases to initiate cellular destruction. However, survival signals can impinge on this pathway and suppress apoptosis. Activation of the Ras-Raf-MEK-ERK mitogen-activated protein kinase (MAPK) pathway is associated with protection of cells from apoptosis and inhibition of caspase-3 activation, although the targets are unknown. Here, we show that the ERK MAPK pathway inhibits caspase-9 activity by direct phosphorylation. In mammalian cell extracts, cytochrome c-induced activation of caspases-9 and -3 requires okadaic-acid-sensitive protein phosphatase activity. The opposing protein kinase activity is overcome by treatment with the broad-specificity kinase inhibitor staurosporine or with inhibitors of MEK1/2. Caspase-9 is phosphorylated at Thr 125, a conserved MAPK consensus site targeted by ERK2 in vitro, in a MEK-dependent manner in cells stimulated with epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA). Phosphorylation at Thr 125 is sufficient to block caspase-9 processing and subsequent caspase-3 activation. We suggest that phosphorylation and inhibition of caspase-9 by ERK promotes cell survival during development and tissue homeostasis. This mechanism may also contribute to tumorigenesis when the ERK MAPK pathway is constitutively activated.
authors.affiliation: Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, UK.
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Allan
authors.forename: Nick
authors.initials: N
authors.lastname: Morrice
authors.forename: Suzanne
authors.initials: S
authors.lastname: Brady
authors.forename: Gareth
authors.initials: G
authors.lastname: Magee
authors.forename: Shalini
authors.initials: S
authors.lastname: Pathak
authors.forename: Paul R
authors.initials: PR
authors.lastname: Clarke
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001483:Base Sequence / Q000235:genetics; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology*; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D003574:Cytochrome c Group / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000187:drug effects / Q000201:enzymology*; D006367:HeLa Cells; D006801:Humans; D048369:MAP Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013912:Threonine / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D011725:Pyridines; D011993:Recombinant Fusion Proteins; C431843:tris(2-pyridylmethyl)amine; D013912:Threonine; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases