CHARACTERIZATION OF THE 5'-FLANKING REGION OF THE GENE FOR THE ALPHA-CHAIN OF HUMAN FIBRINOGEN

The 5'-flanking region of the gene coding for the alpha chain of human fibrinogen was isolated, sequenced, and characterized. The principal site of transcription initiation was determined by primer extension an alysis and the RNase protection assay and shown to be at an adenine re sidue located 55 nucleotides upstream from the initiator methionine co don, or 13,399 nucleotides downstream from the polyadenylation site of the gene coding for the gamma chain. Transient expression of construc ts con containing sequentially deleted 5'-flanking sequences of the al pha chain gene fused to the chloramphenicol acetyltransferase reporter gene showed that the promoter was liver-specific and inducible by int erleukin 6 (IL-6). The shortest DNA fragment with significant promoter activity and full response to IL-6 stimulation encompassed the region from -217 to +1 base pairs (bp). Although six potential IL-6 responsi ve sequences homologous to the type II IL-6 responsive element were pr esent, a single sequence of CTGGGA localized from -122 to -127 bp was shown to be a functional element in IL-6 induction, A hepatocyte nucle ar factor 1 (HNF-1) binding site, present from -47 to -59 bp, in combi nation with other upstream elements, was essential for liver-specific expression of the gene. A functional CCAAT/enhancer binding protein si te (C/EBP, -134 to -142 bp) was also identified within 217 bp from the transcription initiation site. An additional positive element (-1393 to -1133 bp) and a negative element (-1133 to -749 bp) were also found in the upstream region of the alpha-fibrinogen gene.