Differential Regulation of Carcinoembryonic Antigen and Biliary Glycoprotein by γ-Interferon

Carcinoembryonic antigen (CEA), biliary glycoprotein (BGP), and non-specific cross-reacting antigen (NCA) are three closely related cell surface glycoproteins induced by γ-interferon (IFN-γ) in colonic epithelial cells. Maximal induction of CEA by IFN-γ and tumor necrosis factor α (TNF-α) in the colon carcinoma cell line HT-29 occurs at 5–6 days with maximal secreted levels at 14 ng/ml for IFN-γ and 20 ng/ml for TNF-α. Cell viability was reduced to 67% of controls for TNF-α and to 36% for IFN-γ. Dose-response curves showed maximal induction of CEA at 500 units/ml for TNF-α and at 200 units/ml for IFN-γ. Combinations of the two lymphokines revealed that the CEA induction effects were additive and the cytotoxicity effects were synergistic. Northern blot analysis of HT-29 cells treated with IFN-γ and probed with specific probes for BGP, CEA, and NCA showed a 2-fold increase in mRNA level for BGP, and a greater than 10-fold induction for CEA and NCA. Similar results were obtained for the SW403 cell line, but in the case of the LS174T cell line, CEA mRNA levels remained constant before and after IFN-γ treatment, while BGP and NCA mRNA levels increased by 2–5-fold. Polymerase chain reaction analysis of the four alternatively spliced transcripts of BGP revealed no differential induction of one transcript over another by IFN-γ. A comparison of the kinetics of induction of the mRNA levels for BGP and CEA by IFN-γ in the HT29 cell line revealed a half-time of <6 h for BGP and 48 h for CEA. The induction of CEA mRNA was completely inhibited with either cycloheximide (protein synthesis inhibitor) or actinomycin D (RNA synthesis inhibitor), but the induction of BGP mRNA was superinduced by cycloheximide. The difference in the kinetics of induction and effect of cycloheximide on CEA and BGP mRNAs suggest that the two genes are regulated differently in the same cell line. We conclude that the regulation occurs mainly at the posttranscriptional level for CEA and involves mRNA stability. BGP regulation may be more complex, involving transcriptional and posttranscriptional regulation, and more closely resembles the regulation of MHC class II mRNA by IFN-γ in epithelial cells. The mRNA stability effects may be mediated by the dramatically different sequences present in the 3′-untranslated regions of CEA and BGP.