TRANSCRIPTIONAL REGULATION OF THE C1-INHIBITOR GENE BY GAMMA-INTERFERON

Treatment of the hepatoma cell line, Hep3B, with gamma-interferon (IFN ) enhanced expression of C1 inhibitor (C1INH) mRNA, primarily due to a n enhanced transcription rate. Hep3B cells transfected with reporter c onstructs containing various regions of the C1INH gene between positio ns -1182 and +587, and stimulated with gamma-IFN, expressed increased levels of chloramphenicol acetyltransferase in the presence of the fir st intron and as few as 12 bases of the 5'-flanking region. However, a 66% reduction in the inducibility of the constructs was observed when the upstream region between -582 and -252 was eliminated. Successive deletions mapped the first intron IFN-responsive elements to a region between +368 and +410. The data indicate that both the upstream and th e first intron sequences can independently enhance induction of C1INH gene expression. Examination of the immediate upstream sequence of the C1INH gene reveals the absence of a TATA box. The promoter of the C1I NH gene was mapped to a region within 81 bases of the upstream sequenc e and the first exon. Further examination indicated two regions that w ere potentially important for promoter activity as follows: 1) a G-C-r ich region from -81 to -49, and 2) an initiator element at -3 to +5. T he results indicate that the upstream sequences including -81 to -49 a nd the H-DNA region between -48 and -17 are not necessary for promoter activity. The initiator element from -3 to +5 is sufficient and neces sary for promoter function.