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.
The recent finding that sheep had long (l-oPRLR) and short (s-oPRLR) prolactin receptors provided new tools to further explore prolactin signaling to target genes. Here we used CHO cells transfected with l-oPRLR or s-oPRLR cDNAs to compare the activation of known key steps of prolactin signaling by the two receptors. We found that prolactin stimulated l-oPRLR tyrosine phosphorylation, although it lacked the last tyrosine residue found in other long 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 transcription 5 (STAT5), (3) stimulation of transcription from a promoter made of six repeats of STAT5-responsive sequence. However, although it contains STAT5-binding consensus sequences, the ovine beta-lactoglobulin promoter (-4000 to +40) was transactivated by l-oPRLR, but not by s-oPRLR. Taken together, our results indicate that activation of Jak2/STAT5 pathway alone is not sufficient to account for prolactin-induced transcription of this milk protein gene, and that sequences of its promoter, other than STAT5-specific sequences, account for the opposite transcriptional activation capabilities of l-oPRLR and s-oPRLR.
Bignon
C
C
Unité d'Endocrinologie Moléculaire, Bâtiment des Biotechnologies, Institut National de la Recherche Agronomique, 78352, Jouy-en-Josas, France.
Daniel
N
N
Belair
L
L
Djiane
J
J
D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D053614:Janus Kinase 2; D007782:Lactoglobulins / Q000235:genetics*; D008894:Milk Proteins; D011388:Prolactin / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011981:Receptors, Prolactin / Q000235:genetics*; D050799:STAT5 Transcription Factor; D012756:Sheep; D015398:Signal Transduction / Q000235:genetics*; D015534:Trans-Activators / Q000378:metabolism*
D017931:DNA Primers; D004268:DNA-Binding Proteins; D007782:Lactoglobulins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D011981:Receptors, Prolactin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011388:Prolactin; D011505:Protein-Tyrosine Kinases; D053614:Janus Kinase 2