title: Inhibition of apoptosome formation by suppression of Hsp90beta phosphorylation in tyrosine kinase-induced leukemias.
abstract: Constitutively active tyrosine kinases promote leukemogenesis by increasing cell proliferation and inhibiting apoptosis. However, mechanisms underlying apoptotic inhibition have not been fully elucidated. In many settings, apoptosis occurs by mitochondrial cytochrome c release, which nucleates the Apaf-1/caspase-9 apoptosome. Here we report that the leukemogenic kinases, Bcr-Abl, FLT3/D835Y, and Tel-PDGFRbeta, all can inhibit apoptosome function. In cells expressing these kinases, the previously reported apoptosome inhibitor, Hsp90beta, bound strongly to Apaf-1, preventing cytochrome c-induced Apaf-1 oligomerization and caspase-9 recruitment. Hsp90beta interacted weakly with the apoptosome in untransformed cells. While Hsp90beta was phosphorylated at Ser 226/Ser 255 in untransformed cells, phosphorylation was absent in leukemic cells. Expression of mutant Hsp90beta (S226A/S255A), which mimics the hypophosphorylated form in leukemic cells, conferred resistance to cytochrome c-induced apoptosome activation in normal cells, reflecting enhanced binding of nonphosphorylatable Hsp90beta to Apaf-1. In Bcr-Abl-positive mouse bone marrow cells, nonphosphorylatable Hsp90beta expression conferred imatinib (Gleevec) resistance. These data provide an explanation for apoptosome inhibition by activated leukemogenic tyrosine kinases and suggest that alterations in Hsp90beta-apoptosome interactions may contribute to chemoresistance in leukemias.
authors.affiliation: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Box 3813, Durham, NC 27710, USA.
authors.forename: Manabu
authors.initials: M
authors.lastname: Kurokawa
authors.forename: Chen
authors.initials: C
authors.lastname: Zhao
authors.forename: Tannishtha
authors.initials: T
authors.lastname: Reya
authors.forename: Sally
authors.initials: S
authors.lastname: Kornbluth
mesh_terms: D000818:Animals; D053478:Apoptosomes / Q000378:metabolism*; D053477:Apoptotic Protease-Activating Factor 1; D001549:Benzamides; D001854:Bone Marrow Cells / Q000187:drug effects / Q000201:enzymology; D053453:Caspase 9 / Q000378:metabolism; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D016044:Fusion Proteins, bcr-abl; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D007938:Leukemia / Q000201:enzymology* / Q000473:pathology; D051379:Mice; D050505:Mutant Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis* / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology
chemical_list: D053478:Apoptosomes; D053477:Apoptotic Protease-Activating Factor 1; D001549:Benzamides; D018841:HSP90 Heat-Shock Proteins; C493165:HSP90AB1 protein, human; D050505:Mutant Proteins; D010879:Piperazines; D011743:Pyrimidines; D010768:Phosphoserine; D000068877:Imatinib Mesylate; D045304:Cytochromes c; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl; D053453:Caspase 9