Interferon alfa receptor expression and growth inhibition by interferon alfa in human liver cancer cell lines

Type I interferon (IFN) receptor consists of two chains (Hu-IFN-alpha R1 and Hu-IFN-alpha R2), and Hu-IFN-alpha R2 takes a soluble (Hu-IFN-alpha R2a), short (Hu-IFN-alpha R2b), or long (Hu-IFN-alpha R2c) form. We examined the expression of type I IFN receptor, the growth-suppression effect of IFN-alpha, and their relationship in 13 liver cancer cell, lines. With reverse-transcription polymerase chain reaction (RT-PCR) analysis, the expressions of Hu-IFN-alpha R1, Nu-IFN-alpha R2a, and Hu-IFN-alpha R2c were confirmed in all cell lines, and that of Hu-IFN-alpha R2b in 12 cell lines. All cell lines expressed mRNAs of a transcriptional activator, interferon regulatory factor (IRF)-1, and its antagonistic repressor (IRF-2). Flow cytometry revealed weak expression of Hu-IFN-alpha R2 on the cell surface in 12 cell lines. The soluble-form protein of Hu-IFN-alpha R2 was detected at varying levels in culture supernatants of all cell lines with enzyme-linked immunosorbent assay (ELISA). Cell proliferation was suppressed in proportion to the dose of human natural IFN-alpha at 96 hours of culture, but it was not clearly related to the expression of Hu-IFN-alpha R2 protein on the cell surface. Investigations on the morphology, DNA, and cell cycle presented four growth suppression patterns as a result of IFN-alpha: 1) induction of apoptosis and blockage of cell cycle at the S phase (9 cell lines); 2) blockage at the S phase (2 cell lines); 3) induction of apoptosis and blockage at the G(2)/M phase (1 cell line); and 4) blockage at the G(1) phase (1 cell line). There was no evidence showing that changes in the expressions of Bcl-2, Bcl-xL, Bak, and Bar lead directly to IFN-alpha-mediated apoptosis, Our findings demonstrated that IFN-alpha would express growth-suppression effects at varying degrees by inducing inhibition of cell-cycle progression with or without apoptosis, regardless of the expression level of Hu-IFN-alpha R2 protein on the cell surface.