In vitro expression of long and short ovine prolactin receptors: activation of Jak2/STAT5 pathway is not sufficient to account for prolactin signal transduction to the ovine beta-lactoglobulin gene promoter
C. Bignon et al., In vitro expression of long and short ovine prolactin receptors: activation of Jak2/STAT5 pathway is not sufficient to account for prolactin signal transduction to the ovine beta-lactoglobulin gene promoter, J MOL ENDOC, 23(2), 1999, pp. 125-136
The recent finding that sheep had long (l-oPRLR) and short (s-oPRLR) prolac
tin receptors provided new tools to further explore prolactin signaling to
target genes. Here we used CHO cells transfected with l-oPRLR or s-oPRLR cD
NAs to compare the activation of known key steps of prolactin signaling by
the two receptors. We found that prolactin stimulated 1-oPRLR tyrosine phos
phorylation, although it lacked the last tyrosine residue found in other lo
ng prolactin receptors. In addition, l-oPRLR and s-oPRLR both responded to
prolactin stimulation by (1) Janus kinase 2 (Jak2) tyrosine phosphorylation
, (2) DNA-binding activation of signal transducer and activator of transcri
ption 5 (STAT5), (3) stimulation of transcription from a promoter made of s
ix repeats of STAT5-responsive sequence. However, although it contains STAT
5-binding consensus sequences, the ovine P-lactoglobulin promoter (-4000 to
+40) was transactivated by 1-oPRLR, but not by s-oPRLR. Taken together, ou
r results indicate that activation of Jak2/STAT5 pathway alone is not suffi
cient to account for prolactin-induced transcription of this milk protein g
ene, and that sequences of its promoter, other than STAT5-specific sequence
s, account for the opposite transcriptional activation capabilities of 1-oP
RLR and s-oPRLR.