Upregulation of Interferon-α Receptor Expression in Hydroxyurea-Treated Leukemia Cell Lines

Abstract

Background

Interferon-α (IFN-α) shows its antitumor effect through binding to specific cell surface receptors. A DNA synthesis inhibitor, hydroxyurea (HU), has been successfully combined with IFN-α to improve the efficiency of IFN therapy for chronic myelogenous leukemia (CML). To understand the mechanism of this combination effect, expression of IFN-α receptors on the CML cell line, K562, was studied before and after treatment with HU.

Methods

Cells were treated with HU at a dose of 0, 0.1, 0.2, or 0.4 mmol/L for 48 hours. Binding assays were performed using ¹²⁵I-labeled IFN-α at 4°C. Cell cycle analysis was carried out using flow cytometer following staining cellular DNA with propidium iodide. Northern blot analysis was performed to evaluate the inducibility of interferon regulatory factor-1 (IRF-1) gene expression by IFN-α.

Results

Hydroxyurea-treated cells showed a doseand time-dependent increase in binding of ¹²⁵I-labeled IFN-α (maximal 2.5-fold). The increase of binding was caused by an increase in the number of binding sites with a constant receptor affinity. Similar results were obtained in the Burkitt's lymphoma cell line, Daudi. Cell cycle analyses suggested that upregulation of the IFN receptor may have occurred as a result of the alteration in the cell cycle distribution. Furthermore, IFN-α induction of the IFN-inducible gene IRF-1 mRNA in HU-treated K562 cells was 2-fold higher than that in untreated cells.

Conclusions

Thus, HU may have an ability to enhance the response to IFN-α probably because of its ability to upregulate the IFN-α receptors, suggesting that this may be involved in the mechanism of effective combination therapy of IFN-α with HU.