title: Inhibition of protein phosphatase-1 and -2A decreases the chemosensitivity of leukemic cells to chemotherapeutic drugs.
abstract: The phosphorylation of key proteins balanced by protein kinases and phosphatases are implicated in the regulation of cell cycle and apoptosis of malignant cells and influences anticancer drug actions. The efficacy of daunorubicin (DNR) in suppression of leukemic cell survival was investigated in the presence of tautomycin (TM) and calyculin A (CLA), specific membrane permeable inhibitors of protein phosphatase-1 (PP1) and -2A (PP2A), respectively. CLA (50 nM) or TM (1μM) suppressed viability of THP-1 and KG-1 myeloid leukemia cell lines to moderate extents; however, they significantly increased survival upon DNR-induced cell death. CLA increased the phosphorylation level of Erk1/2 and PKB/Akt kinases, the retinoblastoma protein (pRb), decreased caspase-3 activation by DNR and increased the phosphorylation level of the inhibitory sites (Thr696 and Thr853) in the myosin phosphatase (MP) target subunit (MYPT1) as well as in a 25kDa kinase-enhanced phosphatase inhibitor (KEPI)-like protein. TM induced enhanced phosphorylation of pRb only, suggesting that this event may be a common factor upon CLA-induced PP2A and TM-induced PP1 inhibitory influences on cell survival. Silencing PP1 by siRNA in HeLa cells, or overexpression of Flag-KEPI in MCF-7 cells coupled with inducing its phosphorylation by PMA or CLA, resulted in increased phosphorylation of pRb. Our results indicate that PP1 directly dephosphorylates pRb, while PP2A might have an indirect influence via mediating the phosphorylation level of PP1 inhibitory proteins. These data imply the importance of PP1 inhibitory proteins in controlling the phosphorylation state of key proteins and regulating drug sensitivity and apoptosis in leukemic cells.
authors.affiliation: Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Dóra
authors.initials: D
authors.lastname: Dedinszki
authors.affiliation: Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Andrea
authors.initials: A
authors.lastname: Kiss
authors.affiliation: Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden.
authors.forename: László
authors.initials: L
authors.lastname: Márkász
authors.affiliation: Department of Internal Medicine, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Adrienn
authors.initials: A
authors.lastname: Márton
authors.affiliation: Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Emese
authors.initials: E
authors.lastname: Tóth
authors.affiliation: Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institute, Stockholm, Sweden.
authors.forename: László
authors.initials: L
authors.lastname: Székely
authors.affiliation: Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Debrecen, Hungary. Electronic address: erdodi@med.unideb.hu.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Erdődi
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D006367:HeLa Cells; D006801:Humans; D007938:Leukemia / Q000378:metabolism / Q000473:pathology; D061986:MCF-7 Cells; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D043263:Myosin-Light-Chain Phosphatase; C490372:PPP1R12A protein, human; D053148:Caspase 3
keywords: Daunorubicin; KG-1 leukemic cells; Kinase-enhanced protein inhibitor (KEPI) of protein phosphatase-1; Protein phosphatase-1 and -2A; Retinoblastoma protein; THP-1