SERUM RESPONSIVE GENE-EXPRESSION MEDIATED BY SP1

We compared the Spl binding activity of Rata fibroblasts in nuclear ex tracts prepared from quiescent cells and cells stimulated with 20% ser um. 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 minima l adenovirus promoter or an Spl-dependent promoter such as ornithine d ecarboxylase (ODC) containing Spl sites was enhanced following serum s timulation in transient transfection assays. Dephosphorylation of the nuclear extracts with potato acid phosphatase abolished the Spl DNA-bi nding activity, demonstrating a possible correlation between phosphory lation of Spl and DNA-binding activity. These results implicate a pote ntial role for Spl in mediating signal transduction pathways in respon se to mitogenic signals. (C) 1998 Academic Press.