The acute phase response, the systemic response to inflammatory stimuli, consists of a large number of early defensive and adaptive mechanisms which represent a phenomenon of great biologic importance. Our long term goals have been to delineate the mechanisms which mediate the acute phase response, with particular emphasis on C-reactive protein (CRP) induction in hepatocytes. Optimal induction of CRP in the human hepatoma cell line Hep 3B can be accomplished by the combination of IL-6 and IL-1. IL-6 induces transcription of CRP, while IL-1beta, which alone has no effect, significantly enhances the transcriptional effect of IL-6. Our recent studies indicate that a) the transcription factor STAT3 plays an important role in CRP induction by IL-6, an observation which led us to identify a STAT response element in the CRP promoter, b) expression of chimeric constructs of the CRP promoter and a reporter gene (CRP-CAT) are influenced by NFkappaB family members: p50 enhances expression, while p65 blocks this effect, and c) the effect of p50 requires a region in the promoter which contains both STAT and C/EBP response elements but contains no apparent kappaB binding site. These observations give rise to our working hypothesis, that synergistic effects of [IL-6 + IL-1beta] on CRP transcription are mediated by functional interactions between transcription factors activated by IL-1 (most likely NFkappaB family members) and IL-6- responsive STAT or C/EBP family members.
Our specific aims, which are designed to define the precise molecular mechanisms which mediate transcription factor interaction in CRP induction, are: I. To define the role of STAT family members in IL-6 induced transcriptional activation of CRP. II. To determine which transcription factors activated by IL-1beta lead to enhanced CRP gene expression in the presence of IL-6 and to define their response elements III. To elucidate the molecular mechanisms by which interaction between these cytokine-activated transcription factors leads to increased CRP transcription, with particular emphasis on a) requirements for orientation, phase and optimal distance between cis elements, b) the possibility that one transcription factor may enhance binding of another factor to cis elements and c) possible physical contact between factors. These studies will cast light on the molecular mechanisms regulating hepatocyte expression of genes whose products are important to the body's defense mechanisms against infection and tissue injury. They are especially relevant to the elderly, who are particularly vulnerable to these processes.
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