UP-REGULATION OF INTERFERON-ALPHA RECEPTOR EXPRESSION IN HYDROXYUREA-TREATED LEUKEMIA-CELL LINES

Background: Interferon-alpha (IFN-alpha) shows its antitumor effect th rough binding to specific cell surface receptors, A DNA synthesis inhi bitor, hydroxyurea (HU), has been successfully combined with IFN-alpha to improve the efficiency of IFN therapy for chronic myelogenous leuk emia (CML), To understand the mechanism of this combination effect, ex pression of IFN-alpha or receptors on the CML cell line, K562, was stu died before and after treatment with HU. Methods: Cells were treated,v ith HU at a dose of 0, 0.1, 0.2, or 0.4 mmol/L for 48 hours. Binding a ssays were performed using I-125-labeled IFN-alpha at 4 degrees C, Cel l cycle analysis was carried out using flow cytometer following staini ng cellular DNA with propidium iodide, Northern blot analysis was perf ormed to evaluate the inducibility of interferon regulatory factor-1 ( IRF-1) gene expression by IFN-alpha. Results: Hydroxyurea-treated cell s showed a dose- and time-dependent increase in binding of I-125-label ed IFN-alpha (maximal 2.5-fold), The increase of binding was caused by an increase in the number of binding sites with a constant receptor a ffinity, Similar results were obtained in the Burkitt's lymphoma cell line, Daudi, Cell cycle analyses suggested that upregulation of the IF N receptor may have occurred as a result of the alteration in the cell cycle distribution, Furthermore, IFN-alpha induction of the IFN-induc ible gene IRF-1 mRNA in HU-treated K562 cells was 2-fold higher than t hat in untreated cells. Conclusions: Thus, HU may have an ability to e nhance the response to IFN-alpha probably because of its ability to up regulate the IFN-alpha receptors, suggesting that this may be involved in the mechanism of effective combination therapy of IFN-alpha with H U.