Correlation Between Interferon Alpha Receptor Protein Expression and Sensitivity to Interferon Alpha Subtypes in Human Renal Carcinoma Cell Lines

Background: We have previously characterized the antitumor activities and immunological properties of interferon-alpha (IFN-α) subtypes on renal cell carcinoma (RCC). However, the mechanism responsible for the different biologic activities among the IFN-α subtypes is still unclear. To explain the different cellular sensitivities to IFN-α subtypes, detailed expression of the interferon-alpha receptor (IFNAR)-1 and IFNAR-2 subunits on different RCC cell lines was examined and compared with sensitivity of the cell lines to the IFN-α subtypes. Materials and Methods: We investigated the antiproliferative effects of natural IFN-α subtypes (IFN-α2 and IFN-α8) using eight RCC cell lines. IFNAR-1 and IFNAR-2 expression were determined by RT-PCR and Western blotting. To determine a possible relationship between IFN activity and IFNAR expression, the correlation between the 50% effective IFN dose (ED 50 ) for growth inhibition and the level of IFNAR expression was statistically examined. Results: We report here that IFN-α8 more potently induced growth inhibition than IFN-α2 in the majority of the RCC cell lines examined, this being in accordance with our previous results. The ED 50 value of IFN-α8 was lower than 1000 (IU/ml) in six of the eight cell lines, whereas that of IFN-α2 was lower than 1000 (IU/ml) in three of the eight cell lines. The results of experiments using Western blotting analysis revealed that IFN-α subtype sensitivities were closely correlated with the expression level of IFNAR-2(c), a long form of the IFNAR-2 protein, in seven of the eight cell lines. Conclusion: These results suggest that the intensity of IFNAR-2(c) protein expression could be an important prognostic marker for clinical application of particular IFN-α subtypes in RCC.