NONPITUITARY HUMAN PROLACTIN GENE-TRANSCRIPTION IS INDEPENDENT OF PIT-1 AND DIFFERENTIALLY CONTROLLED IN LYMPHOCYTES AND IN ENDOMETRIAL STROMA

Expression of the human PRL (hPRL) gene in extrapituitary sites such a s the uterus (decidualized endometrial stroma and myometrium) and cell s of the hematopoietic lineage is directed by an alternative promoter which is located approximately 6 kilobases (kb) upstream of the pituit ary-specific start site. In order to delineate the tissue-specific mec hanisms governing the control of nonpituitary PRL gene expression, we have cloned and sequenced 3 kb 5'-flanking DNA of the upstream decidua l/lymphoid (dPRL) promoter. Based on sequence homology we identified t wo binding motifs for Pit-1 and seven half-sites for glucocorticoid re ceptor/progesterone receptor (PR) binding. We focused our studies on t he role of Pit-1 and of PR as potential transcriptional regulators, si nce the POU domain protein Pit-1 is essential in the control of pituit ary PRL expression, and progesterone induces decidual transformation o f the endometrial stroma, a differentiation process during which the d ecidual PRL gene is activated. We demonstrate in a variety of cell typ es, including lymphocytes and endometrial stroma, that Pit-1 is not in volved in the regulation of dPRL promoter/reporter gene constructs car rying 3 kb 5'-flanking DNA. Our experiments also show that activated P R does not confer direct transcriptional control on the dPRL promoter. When we compared the activity of the transfected dPRL promoter in PRL -secreting and nonsecreting lymphoid cells, we found that the 3 kb 5'- flanking region of the dPRL promoter did not contain elements restrict ing expression to only those lymphocytes that produce PRL but allowed expression of fusion reporter genes irrespective of the status of the endogenous PRL gene. This was in sharp contrast to endometrial cells w here 3 kb 5'-flanking DNA conferred strong transcriptional activation on the dPRL promoter in decidualized endometrial stromal cells activel y secreting PRL, but did not allow transcription in undifferentiated n on-PRL-secreting endometrial stromal cells. Activation of the dPRL pro moter construct in these undifferentiated cells could however be induc ed by the addition of cAMP, in the absence of progesterone, suggesting that a signal transduced through the cAMP signaling pathway is a prim ary inducer of decidual PRL gene expression.