ROLE OF TRANSFORMING-GROWTH-FACTOR (TGF)-BETA TYPE-I AND TGF-BETA TYPE-II RECEPTORS IN THE TGF-BETA-1-REGULATED GENE-EXPRESSION IN PITUITARY PROLACTIN-SECRETING LACTOTROPES

Transforming growth factor beta 1 (TGF-beta 1) inhibits pituitary lact otrope proliferation and secretion of PRL in an autocrine/paracrine ma nner. In this study, the role of TGF-beta 1 type I (T beta R-I) and TG F-beta type II (T beta R-II) receptors in TGF-beta 1-regulated gene ex pression in lactotropes was determined using anterior pituitary cells known to be responsive to TGF-beta 1 growth inhibition and using a tra nsformed PR1 cell Line known to be nonresponsive to TGF-beta I growth inhibition. Treatment with TGF-beta 1 inhibited cell proliferation and decreased PRL mRNA levels in anterior pituitary cells, but in PR-1 ce lls, the treatment caused only decreased PRL mRNA levels. Affinity lab eling of TGF-beta binding proteins indicated that anterior pituitary c ells contain several TGF-beta-binding protein complexes, including the 65 kDa size T beta R-I and 95 kDa size T beta R-II. In the PR1 cells, the major complex found was similar to the 65 kDa size of T beta R-I. Immunocytochemistry identified T beta R-I and T beta R-II receptor pr oteins in lactotropes but detected primarily T beta R-I receptor prote in in PR1 cells. RT-PCR detection of T beta R-I and T beta R-II mRNA i dentified both receptor mRNA transcripts in anterior pituitary cells a nd in PR1 cells but the levels of T beta R-II and T beta R-I mRNA tran scripts in PR1 cells was much lower than that in anterior pituitary ce lls. Determination of the TGF-beta 1 gene responses in PR1 cells follo wing T beta R-I and T beta R-II gene transfection indicated that PR1 c ells transactivate transcription of the TGF-beta-responsive p3TP-Lux r eporter in the absence of cotransfected T beta R-II receptor. The intr oduction of the T beta R-II receptor alone or in combination with T be ta R-I confer ligand-independent reporter transactivation in these cel ls. When only T beta R-I was introduced along with reporter, a ligand- dependent transactivation was observed. These data suggest for the fir st time that the TGF-beta 1-mediated transcriptional activation respon se can be distinguished from the growth response in lactotropes. Furth ermore, the TGF-beta I gene-transcription response is less dependent o n T beta R-II receptor expression than is the TGF-beta I growth-inhibi tory response.