Reduction in p48-ISGFγ Levels Confers Resistance to Interferon-α2a in MHCC97 Cells.

Objectives: Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies in China and, due to the limited efficacy of currently available therapies, is responsible for a large number of deaths. IFN-α therapy has shown promise in the treatment of various forms of human cancer and is considered in the treatment of HCC. Previous results from our group showed that high doses of IFN-α exert a significant antiproliferative effect on MHCC97 human xenografts in nude mice, but not on MHCC97 cells when tested in vitro. Here we present experiments designed to characterize the molecular mechanism underlying the defective response of MHCC97 cells to IFN-α. Elucidation of the mechanism underlying the defective response of MHCC97 to IFN-α may help to explain and possibly to overcome clinical failures of this form of tumor therapy. Methods: IFN-α2a was administered between 3,000 and 10,000 IU/ml, a range strongly inhibiting proliferation in other cell lines. Gene expression profiles of MHCC97 cells were obtained before and after treatment with IFN-α2a using cDNA microarray analysis. The transcriptional activity of relevant genes responding to IFN-α2a in the cDNA microarray experiments was confirmed by RT-PCR and Northern blot analysis. Transient transfection with an expression vector was used to restore p48-ISGFγ (IRF9) protein levels. Cell proliferation was evaluated using the MTT assay. Results: Although IFN-α treatment caused the activation of several signal transduction pathways in MHCC97 cells, the lack of an antiproliferative effect was found to mainly derive from a defect in the activation of the transcription factor ISGF3 required for Jak/STATS signaling. We show that the defect in ISGF3 activation is mainly caused by the absence of one of its essential components, the protein p48-ISGFγ from MHCC97 cells. Indeed, transient expression of p48-ISGFγ restores sensitivity to IFN-α2a. Although the mRNA levels of p48-ISGFγ were normal in MHCC97 cells, mutations could be detected in the gene coding for the protein. We hypothesize, therefore, that these mutations alter the message or protein stability, leading to the reduced protein levels observed. Conclusion: Our results confirm the important role of Jak/STATS signaling in the antiproliferative effects of IFN-α in tumor cells and indicate that defects in ISGF3 can cause resistance to IFN-α2a treatment. Copyright © 2004 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]