title: PKC alpha mediates chemoresistance in acute lymphoblastic leukemia through effects on Bcl2 phosphorylation.
abstract: Overexpression of protein kinase C alpha (PKC alpha) promotes Bcl2 phosphorylation and chemoresistance in human acute leukemia cells. The contribution of non-Bcl2 mechanisms in this process is currently unknown. In this report, overexpression of PKC alpha was found not to affect cell proliferation, cell cycle, or activation of mitogen-activated protein kinases. The failure of PKC alpha overexpression to activate non-Bcl2 survival pathways suggested that PKC alpha-mediated chemoresistance requires Bcl2. Supporting this notion, REH/PKC alpha transfectants were found to be as sensitive to HA14-1 (a drug that targets Bcl2 function) as parental cells. In addition, HA14-1 abrogated PKC alpha's ability to protect REH cells from etoposide. These findings suggested that Bcl2 is necessary for the protective function of PKC alpha in REH cells. Since Bcl2 phosphorylation status is negatively regulated by protein phosphatase 2A (PP2A) and PP2A regulates PKC alpha, we investigated whether PKC alpha can conversely regulate PP2A. Overexpression of PKC alpha was found to suppress mitochondrial PP2A activity by a mechanism that, at least in part, involves suppressed expression of the regulatory subunit comprising the Bcl2 phosphatase (ie the PP2A/B56 alpha subunit). The ability of PKC alpha to target both Bcl2 and the Bcl2 phosphatase represents a novel mechanism for chemoresistance.
authors.affiliation: Division of Cell Signaling, Institute of Molecular Medicine, University of Texas Health Science Center, Houston, TX 77030, USA.
authors.forename: T
authors.initials: T
authors.lastname: Jiffar
authors.forename: S
authors.initials: S
authors.lastname: Kurinna
authors.forename: G
authors.initials: G
authors.lastname: Suck
authors.forename: D
authors.initials: D
authors.lastname: Carlson-Bremer
authors.forename: M R
authors.initials: MR
authors.lastname: Ricciardi
authors.forename: M
authors.initials: M
authors.lastname: Konopleva
authors.forename: M
authors.initials: M
authors.lastname: Andreeff
authors.forename: P P
authors.initials: PP
authors.lastname: Ruvolo
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D001578:Benzopyrans / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000201:enzymology* / Q000473:pathology; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D054648:Protein Phosphatase 2; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D001578:Benzopyrans; D004791:Enzyme Inhibitors; D009570:Nitriles; D019253:Proto-Oncogene Proteins c-bcl-2; C456800:ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate; D005047:Etoposide; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2