Defective Jak-Stat activation in hepatoma cells is associated with hepatitis C viral IFN-α resistance

Interferon-alpha ( IFN-alpha) has been widely used to treat viral infections and certain types of cancers. Large numbers of patients with chronic hepatitis C viral ( HCV) infection do not respond to IFN and ribavirin combination therapy, and the majority of patients do not respond to IFN monotherapy. The underlying mechanisms of HCV nonresponse to IFN are unknown. In this report, using a HCV subgenomic replicon cell culture system, we show that ( 1) long- term IFN stimulation can select cells defective for Stat3 activation, and the defect appears to be responsible for HCV IFN resistance in cell culture, ( 2) HCV subgenomic sequence mutations associated with long- term culture do not appear to be responsible for IFN resistance, ( 3) expression of the activated Stat3 reverses IFN resistance while a dominant negative form of Stat3 renders an IFN- sensitive cell line resistant to IFN, and ( 4) the IFN- resistant cell line exhibits enhanced suppressor of cytokine signaling 3 ( SOCS3) expression in response to IFN stimulation, and blocking SOCS3 in the IFN- resistant cell line partially restores IFN sensitivity. These findings strongly suggest that the IFN- resistant phenotype in vitro is associated with defective Stat3 activation and an enhanced SOCS3 response but is not associated with viral sequence mutations. Our study implies that long- term IFN stimulation in vitro selects cells that exhibit alterations in the host Jak- Stat signaling pathway, thereby representing a potential mechanism by which HCV resists IFN therapy.