[Regulation of the complement C3 gene expression: regulatory elements required for cytokine-induced expression]

Abstract

I isolated murine and human genomic cosmid clones of complement C3 gene and sequenced 5'-flanking region of their transcriptional initiation sites to determine cis-elements that participate in regulation of C3 gene expression. The murine and human 5'-flanking regions are 51% identical overall, with positions -36 to -1 and -146 to -68 showing 80% identity. Four TATA boxes were identified upstream of the murine transcriptional initiation site, but only the TATA element at position -30 is essential for expression of murine C3 in hepatocytes. Deletion and transfection analysis indicated that sequences -395 to -111 are essential for constitutive expression of C3 gene and suggested that sequences between -1457 and -800 contain regulatory elements that are involved in suppressing basal expression. Mutation analyses showed that sequences between -88 and -83 are essential for IL-6 responsiveness and both sequences between -88 and -83 and -77 to -72 are necessary for enhancer activity and responsiveness to IL-1. These sequences are highly homologous to binding sites of DNA binding proteins, C/EBP and NF-kappa B, respectively. Collectively, these results localize cis-acting elements involved in constitutive and IL-1/IL-6-regulated murine C3 gene expression, and provide implication for specific trans-acting factors.