Saydam, G..Aydin H.H.Sahin F.Selvi N.Oktem G.Terzioglu E.Buyukkececi F.Omay S.B.2019-10-272019-10-2720030145-2126https://doi.org/10.1016/S0145-2126(02)00347-8https://hdl.handle.net/11454/27870Interferon-alpha (IFN-?)-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-?-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-?-2b induced K562 cytotoxicity. Trypan blue dye exclusion test and MTT assay were utilised for determining cytotoxicity. IC50 of IFN-?-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-?-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-?-2b induced apoptosis of K562 cells and should be investigated as a new window furthermore. © 2003 Elsevier Science Ltd. All rights reserved.en10.1016/S0145-2126(02)00347-8info:eu-repo/semantics/closedAccessApoptosisInterferon-?-2bK562 cellsPP2AArticle27870971712801529N/A