Role of interferon regulatory factor-1 in the induction of biliary glycoprotein (cell CAM-1) by interferon-gamma.

Biliary glycoprotein (BGP), also known as C-CAM-1, has been shown to be down-regulated in colon and prostate tumors. Previously, we demonstrated that BGP mRNA is up-regulated by interferon-gamma (IFN-gamma) in colon cancer cell lines (Takahashi, H., Okai, Y., Paxton, R. J., Hefta, L. J. F., and Shively, J. E. (1993) Cancer Res. 53, 1612-1619). We now show that the BGP promoter contains an interferon-sensitive response element (ISRE) that is specifically protected in in vivo footprints. Interferon regulatory factor-1 (IRF-1) was identified as the ISRE-binding factor by electrophoretic mobility shift assays. The induction of IRF-1 mRNA by IFN-gamma in HT-29 cells reaches a maximum at 6 h and is superinduced by cycloheximide. Four mRNA species for BGP are induced by IFN-gamma, the major band of which is inhibited by cycloheximide. Transfection of HT-29 cells with an IRF-1 expression plasmid (pAct-1) transactivates a BGP promoter reporter gene containing wild-type (but not mutant) ISRE. Electrophoretic mobility shift assay analysis of a second footprint reveals the binding of Sp1, an Sp1-like protein, and upstream stimulatory factor. The Sp1-like complex was also induced by IFN-gamma treatment of HT-29 cells and may be a second point of transcriptional control for the BGP gene.