Suppression of UV- and interferon-α-refractoriness by antipain in human IFr cells established from RSa cells sensitive to both stimuli

The human cell line IF^r is a variant with an increased resistance to cell proliferation inhibition (CPI) by human interferon (HuIFN)-α, established from RSa cells with unusually high-sensitivity to CPI. IF^r cells were later found to have increased resistance to the cell-killing effects of far-ultraviolet (UV) irradiation. Here, in cell lysates extracted from UV-irradiated IF^r cells but not in those from irradiated RSa cells, fibrinolytic protease activity was found to be elevated promptly and transiently after irradiation. Treatment of IF^r cells with HuIFN-α alone also resulted in the elevation of protease activity, but not that of RSa cells. Both the activity elevated after UV irradiation and after HuIFN-α treatment was inhibited to the greatest extent by antipain in vitro. Moreover, the refractoriness of IF^r cells to UV cell-killing and to HuIFN-α CPI was suppressed by culturing with medium containing antipain immediately after UV irradiation or during HuIFN-α exposure. In similarly treated RSa cells, there was no modulation of UV- or HuIFN-α-susceptibility. These comparative characteristics between the two cell lines suggested that antipain-sensitive proteases and/or cellular functions may be involved in increased resistance to UV and HuIFN-α of IF^r cells. © 1996 Wiley-Liss, Inc.