Ts. Schaefer et al., COOPERATIVE TRANSCRIPTIONAL ACTIVITY OF JUN AND STAT3-BETA, A SHORT-FORM OF STAT3, Proceedings of the National Academy of Sciences of the United Statesof America, 92(20), 1995, pp. 9097-9101
To identify proteins that regulate the transcriptional activity of c-J
un, we have used the yeast two-hybrid screen to detect mammalian polyp
eptides that might interact functionally with the N-terminal segment o
f c-Jun, a known regulatory region, Among the proteins identified is a
short form of Stat3 (designated Stat3 beta), Stat3 beta is missing th
e 55 C-terminal amino acid residues of the long form (Stat3 alpha) and
has 7 additional amino acid residues at its C terminus, In the absenc
e of added cytokines, expression of Stat3 beta (but not Stat3 alpha) i
n transfected cells activated a promoter containing the interleukin 6
responsive element of the rat alpha(2)-macroglobulin gene; coexpressio
n of Stat3 beta and c-Jun led to enhanced cooperative activation of th
e promoter, Nuclear extracts of cells transfected with a Stat3 beta ex
pression plasmid formed a complex with an oligonucleotide containing a
Stat3 binding site, whereas extracts of cells transfected with a Stat
3 alpha plasmid did not, We conclude that there is a short form of Sta
t3 (Stat3 beta), that Stat3 beta is transcriptionally active under con
ditions where Stat3 alpha is not, and that Stat3 beta and c-Jun are ca
pable of cooperative activation of certain promoters.