title: Transforming growth factor beta1 is a paracrine inhibitor of prolactin gene expression.
abstract: We have shown previously that rat mammotropes produce an activity that suppresses PRL gene expression by neighboring mammotropes. Here, we tested the hypothesis that this mammotrope-derived inhibitor is transforming growth factor-beta1 (TGFbeta1). To this end, we pursued a two-pronged strategy wherein we added exogenous TGFbeta1 to primary cultures of anterior pituitary cells transfected with a rat PRL-luc construct. Measurement of luciferase activity by luminometry of extracts revealed that administration of TGFbeta1, over a range of doses shown by others to be secreted by cultures of pituitary cells, caused a significant (P < 0.05) suppression of PRL gene expression. In contrast, immunoremoval of secreted TGFbeta1 led to an elevation of PRL promoter-driven reporter activity in these cultures. In a subsequent study, we repeated these experiments with a single cell model in an attempt to determine the demographics of the cellular responses. Accordingly, we transfected (via microinjection) individual mammotropes with the rat PRL-luc construct; exposed them to TGFbeta1, its neutralizing antibody, or respective controls; and then assessed PRL gene expression in "real-time" by quantification of photons emitted by the living cells after exposure to the substrate luciferin. Our results revealed that 1) TGFbeta1 inhibited PRL gene expression in all mammotrope studied; 2) only a subgroup of mammotropes (approximately 23%) was relieved of TGFbeta1 inhibition by antibody treatment; and 3) the growth factor exerted its inhibitory effect via a paracrine, as opposed to an autocrine, mechanism. These findings identify TGFbeta1 as the paracrine agent that exerts a tonic inhibitory influence over PRL gene expression in mammotropes.
authors.affiliation: Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Abraham
authors.forename: W J
authors.initials: WJ
authors.lastname: Faught
authors.forename: L S
authors.initials: LS
authors.lastname: Frawley
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D019899:Paracrine Communication / Q000502:physiology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000502:physiology; D011388:Prolactin / Q000037:antagonists & inhibitors* / Q000235:genetics*; D051381:Rats; D011919:Rats, Inbred Strains; D016212:Transforming Growth Factor beta / Q000276:immunology / Q000494:pharmacology*
chemical_list: D000906:Antibodies; D016212:Transforming Growth Factor beta; D011388:Prolactin