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Transforming growth factor-beta 1 messenger RNA and protein expression in the pituitary gland: its action on
D K Sarkar1, K H Kim, S Minami
1Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman 99164.
Abstract:
Transforming growth factor-beta 1 (TGF-beta 1) is known to inhibit cell growth and proliferation of many estrogen-responsive normal and transformed cells. The effect of this polypeptide growth factor on the estrogen-responsive pituitary lactotropes has not been determined. To evaluate the role of TGF-beta 1 in the control of lactotropic growth, the action and production of TGF-beta 1 in the anterior pituitary was studied in rats. The growth factor suppressed basal PRL release from the primary culture of enriched rat lactotropes in a concentration-dependent manner in the range of 2 pg/ml-20 ng/ml. The growth factor did not affect the secretion of other pituitary hormones in the cultures. The inhibitory action of TGF-beta 1 on PRL release was time dependent. The minimum time required to produce a significant effect was 4 h. The growth factor also suppressed estradiol-induced PRL release as well as it inhibited estradiol-induced proliferation of lactotropes. TGF-beta 1 immunoreactivity was detected in the cellular extracts of cultured anterior pituitary cells and in the extracts of anterior pituitary tissue. In addition, the primary culture of enriched rat lactotropes secreted TGF-beta 1. Using Northern blot techniques, a 2.4-kilobase transcript of pro-TGF-beta 1 mRNA was detected both in the anterior pituitary tissue and in the primary culture of anterior pituitary cells. These data suggest that TGF-beta 1 is produced in the pituitary gland and inhibits the secretion of PRL and growth of lactotropes in an autocrine and/or paracrine fashion.
Insights
Transforming growth factor-beta 1 (TGF-beta 1) inhibits prolactin (PRL) release and lactotrope growth in rats. This pituitary growth factor is produced locally, suggesting autocrine or paracrine roles in regulating PRL secretion.
Area of Science:
- Endocrinology
- Cell Biology
- Molecular Biology
Background:
- Transforming growth factor-beta 1 (TGF-beta 1) inhibits many estrogen-responsive cells.
- The role of TGF-beta 1 in estrogen-responsive pituitary lactotropes was previously unknown.
Purpose of the Study:
- To investigate the action and production of TGF-beta 1 in the rat anterior pituitary.
- To determine if TGF-beta 1 influences lactotropic growth and prolactin (PRL) secretion.
Main Methods:
- Primary cultures of enriched rat lactotropes were used to assess TGF-beta 1 effects on hormone release and cell proliferation.
- TGF-beta 1 production was evaluated using immunoreactivity and Northern blot analysis for pro-TGF-beta 1 mRNA.
Main Results:
- TGF-beta 1 suppressed basal and estradiol-induced PRL release in a concentration- and time-dependent manner.
- TGF-beta 1 also inhibited estradiol-induced lactotrope proliferation.
- TGF-beta 1 and its mRNA were detected in anterior pituitary tissue and cultured lactotropes, indicating local production.
Conclusions:
- TGF-beta 1 is produced within the pituitary gland.
- TGF-beta 1 inhibits PRL secretion and lactotrope growth, likely through autocrine and/or paracrine mechanisms.