title: Involvement of protein phosphatase 2A in interferon-alpha-2b-induced apoptosis in K562 human chronic myelogenous leukaemia cells.
abstract: Interferon-alpha (IFN-alpha)-2b is known to have antiproliferative effects on hematological malignant cells, especially chronic myelogenous leukaemia (CML). However, it can induce cytogenetical remissions in a very small percentage of the patients. Also during interferon therapy, resistance can emerge in the CML clones. K562 is an in vitro model cell line transformed from a Ph positive CML patient. It can be induced to differentiate to granulocytic and/or monocytic lineages with certain molecules. IFN-alpha-2b generally exerts its effects on CML cells by Janus family kinases (Jak/Stat) pathway, mostly through tyrosine kinase system. However, there is almost no data on the relevance of serine/threonine (Ser/Thr) protein phosphatase (PP) system in the interferon induced signal transduction pathways. In this study, we investigated serine/threonine protein phosphatases in the IFN-alpha-2b induced K562 cytotoxicity. Trypan blue dye exclusion test and MTT assay were utilised for determining cytotoxicity. IC(50) of IFN-alpha-2b on K562 cells was found to be 600IU/ml. However, no differentiation was determined by analysis of cell surface antigen expressions. Serine/threonine protein phosphatase inhibitors calyculin A (Cal A) and okadaic acid (OKA) augmented the IFN-alpha-2b induced cytotoxicity. Apoptosis assay by the mono-oligonucleosome detection and acridine orange/propidium iodide dye revealed marked apoptosis underlying cytotoxicity. Phosphatase enzyme assay revealed a gradual increase in protein phosphatase 2A (PP2A) activity during interferon induced cytotoxicity. Conversely, immunoblots showed no change in the expression of PP2A catalytic and regulatory subunits. In conclusion, PP2A plays a role in IFN-alpha-2b induced apoptosis of K562 cells and should be investigated as a new window furthermore.
authors.affiliation: Department of Hematology, School of Medicine, Ege University, Bornova, TR-35100 Izmir, Turkey.
authors.forename: Guray
authors.initials: G
authors.lastname: Saydam
authors.forename: Hikmet Hakan
authors.initials: HH
authors.lastname: Aydin
authors.forename: Fahri
authors.initials: F
authors.lastname: Sahin
authors.forename: Nur
authors.initials: N
authors.lastname: Selvi
authors.forename: Gulperi
authors.initials: G
authors.lastname: Oktem
authors.forename: Ender
authors.initials: E
authors.lastname: Terzioglu
authors.forename: Filiz
authors.initials: F
authors.lastname: Buyukkececi
authors.forename: Serdar Bedii
authors.initials: SB
authors.lastname: Omay
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020128:Inhibitory Concentration 50; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000494:pharmacology*; D020014:K562 Cells; D007700:Kinetics; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy / Q000473:pathology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D054648:Protein Phosphatase 2; D021122:Protein Subunits / Q000032:analysis; D011994:Recombinant Proteins
chemical_list: D004791:Enzyme Inhibitors; D000077190:Interferon alpha-2; D016898:Interferon-alpha; D021122:Protein Subunits; D011994:Recombinant Proteins; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2