Functional characterization of promoter elements involved in regulation of human B beta-fibrinogen expression. Evidence for binding of novel activator and repressor proteins.

A high level of plasma fibrinogen has been shown to be an important risk factor for myocardial infarction and stroke. Thus, we were prompted to investigate regulation of human fibrinogen biosynthesis, a process wherein expression of the B beta-chain of fibrinogen appears to be rate-limiting for fibrinogen secretion. Using electrophoretic mobility shift assays with synthetic probes representing portions of the human B beta-fibrinogen promoter, we have defined several elements that bind distinct classes of transcription factors present in human hepatoma cell nuclear extracts. The contribution of each element to promoter activity was demonstrated in transfection experiments using promoter-chloramphenicol acetyltransferase constructs and human hepatoma cells. Our observations indicate that two distinct sequence elements are required for maximal induction of transcription by interleukin-6. One of these sequences is an IL-6-RE core element similar to that reported for the rat alpha 2-macroglobulin promoter and the other is a binding site for the C/EBP family of transcription factors. We also report two additional elements, one negative- and one positive-acting, that bind novel sequence-specific factors.