Cooperative transcriptional activity of Jun and Stat3β, a short form of Stat3

Abstract

To identify proteins that regulate the transcriptional activity of c-Jun, we have used the yeast two-hybrid screen to detect mammalian polypeptides that might interact functionally with the N-terminal segment of c-Jun, a known regulatory region. Among the proteins identified is a short form of Stat3 (designated Stat3β). Stat3β is missing the 55 C-terminal amino acid residues of the long form (Stat3α) and has 7 additional amino acid residues at its C terminus. In the absence of added cytokines, expression of Stat3β (but not Stat3α) in transfected cells activated a promoter containing the interleukin 6 responsive element of the rat α2-macroglobulin gene; coexpression of Stat3β and c-Jun led to enhanced cooperative activation of the promoter. Nuclear extracts of cells transfected with a Stat3β expression plasmid formed a complex with an oligonucleotide containing a Stat3 binding site, whereas extracts of cells transfected with a Stat3α plasmid did not. We conclude that there is a short form of Stat3 (Stat3β), that Stat3β is transcriptionally active under conditions where Stat3α is not, and that Stat3β and c-Jun are capable of cooperative activation of certain promoters.