PROLACTIN GENE-EXPRESSION IN HUMAN MYOMETRIAL SMOOTH-MUSCLE CELLS IS INDUCED BY CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE

We have previously characterized PRL production in human myometrial ti ssue maintained in explant culture. Here we describe PRL gene expressi on and its regulation in smooth muscle cells isolated from normal huma n myometrium. Onset of PRL secretion occurred spontaneously after seve ral days in culture and increased over time without exogenous stimulat ion. PRL secretion could be further stimulated by the addition of PGE( 2) or relaxin, both of which were also shown to increase cAMP formatio n in smooth muscle cells. Likewise, treatment with 8-Br-cAMP led to an elevation of PRL secretion. By reverse transcription/polymerase chain reaction, we demonstrate that smooth muscle cells transcribe the PRL gene from the alternative decidual-type dPRL promoter, located upstrea m of the pituitary promoter. Treatment with PGE(2), relaxin, and 8-Br- cAMP resulted in an increase in dPRL transcript abundancy. The effect of cAMP was transcriptional as shown by the induction of transfected d PRL promoter/reporter gene fusion constructs. A fragment of 332 bp fla nking the dPRL transcription start site was sufficient to mediate cAMP inducibility. In parallel with the increase in PRL secretion, we dete cted an increase in cAMP formation and PGE(2) secretion in cultured sm ooth muscle cells. We propose the presence of a paracrine positive fee dback mechanism that may reflect the physiological situation in vivo w here an increase in myometrial adenylate cyclase activity throughout p regnancy has been reported.