Serum responsive gene expression mediated by Sp1

We compared the Spl binding activity of Rata fibroblasts in nuclear extracts prepared from quiescent cells and cells stimulated with 20% serum. Increased DNA-binding activity was observed in extracts from serum-stimulated cells when an Spl oligonucleotide was used as radiolabeled probe in electrophoretic mobility shift assays. This increase in Spl DNA-binding activity is not due to changes in the amount of Spl in the nucleus as shown by immunoblot analysis. The transcriptional activity of a reporter construct containing six Spl sites upstream of a minimal adenovirus promoter or an Spl-dependent promoter such as ornithine decarboxylase (ODC) containing Spl sites was enhanced following serum stimulation in transient transfection assays. Dephosphorylation of the nuclear extracts with potato acid phosphatase abolished the Spl DNA-binding activity, demonstrating a possible correlation between phosphorylation of Spl and DNA-binding activity. These results implicate a potential role for Spl in mediating signal transduction pathways in response to mitogenic signals. (C) 1998 Academic Press.