Pituitary lactotrope expresses transforming growth factor beta (TGF beta) type II receptor mRNA and protein and contains 125I-TGF beta 1 binding sites.
Transforming growth factor beta 1 (TGF beta 1) has recently been shown to be produced in the prolactin (PRL)-secreting lactotropes of the pituitary gland. TGF beta 1 inhibits lactotropic secretion and proliferation, and the production of TGF beta 1 in lactotropes is reduced during lactotropic growth following estrogen treatment in ovariectomized rats. In many estrogen-responsive tissues, TGF beta 1 has been shown to exert its effect by binding to TGF beta 1 type II receptors (T beta R II) at the cell surface. In this study, we sought to ascertain whether T beta R II is involved in TGF beta 1 action on lactotropes by determining the changes of T beta R II mRNA and protein levels and specific 125I-TGF beta 1 binding sites on the lactotropes during estrogen-induced proliferation of lactotropes in Fischer 344 rats. Double immunohistochemical procedures were employed to identify immunoreactive T beta R II in PRL-reactive cells. The majority of T beta R II-reactive cells in the anterior pituitary were observed to be lactotropes. Dual immunohistochemistry and in situ hybridization procedures also indicated that lactotropes were the major cell types containing T beta R II mRNA hybrids. Both the levels of immunoreactive T beta R II protein and in situ T beta R II mRNA hybrids in the pituitary were significantly decreased in ovariectomized rats after 15 days of estrogen treatment. Determination of 125I-TGF beta 1 binding sites in lactotropes by double immunohistochemistry and receptor autoradiography also revealed specific binding sites of 125I-TGF beta 1 in lactotropes in the anterior pituitary. 125I-TGF beta 1 binding in the anterior pituitary was also reduced following estrogen treatment in ovariectomized rats. These data suggest that down-regulation of T beta R II may be an important mechanism of estrogen action on lactotropic cell growth and PRL secretion, and further support the notion that TGF beta 1 controls lactotropic function by autocrine/paracrine mechanisms.
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Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman 99164-6520, USA.
Morgan
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Speth
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Boyadjieva
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Sarkar
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DK
D000818:Animals; D001665:Binding Sites; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D004958:Estradiol; D011388:Prolactin; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II