Regulation of C4b-binding protein gene expression by the acute-phase mediators tumor necrosis factor-alpha, interleukin-6, and interleukin-1

Abstract

C4b-binding protein (C4BP) is involved in the fluid-phase regulation of the classical pathway of complement. During an acute-phase response, we have shown that hepatic levels of murine C4BP mRNA are elevated 2.5-fold while rat liver C4BP gene expression exhibits a 4-fold induction. Furthermore, a survey of different mouse tissues showed that during acute inflammation C4BP gene expression was confined to the liver. To gain a better understanding of the acute-phase regulation of C4BP gene expression we utilized the rat hepatoma cell line FAO in which tumor necrosis factor-alpha (TNF-alpha) produced a 2.7-fold induction of C4BP mRNA levels. In the absence of TNF-alpha, interleukin-1 alpha (IL-1 alpha) and interleukin-6 (IL-6) had little effect on C4BP gene expression but when all three cytokines were used together a synergistic 4-fold induction of C4BP mRNA levels was observed. In contrast the synthetic glucocorticoid dexamethasone inhibited TNF-alpha-induced C4BP gene expression. Cycloheximide-mediated inhibition of inducible C4BP gene expression demonstrated the requirement for ongoing protein synthesis. Rapid induction of C4BP mRNA levels by TNF-alpha and IL-6 (within 1 h) and the observation that stimulation was inhibited by actinomycin D provided evidence that regulation of C4BP gene expression during the acute-phase response is regulated at the transcriptional level. Isolation of a genomic clone extending into the 5' regulatory region of the rat C4BP gene enabled us to identify the major transcriptional start site and putative response elements through which TNF-alpha, IL-6, IL-1 alpha, and dexamethasone may exert their effects on C4BP gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)