GROWTH FACTOR INVOLVEMENT IN PITUITARY FUNCTION

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Prolactin secreting adenomata are a common cause of amenorrhea and infertility. tumors fortunately usually retain hormonal responsiveness such that their hormone production and growth can be controlled by the same hormones that modulate their normal counterparts. We have proposed that the growth of pituitary lactotrophs is regulated by growth factors whose expression in the pituitary gland is regulated hormonally. Previously we have localized transforming growth factor-alpha (TGFalpha) to lactotrophs and propose that this growth factor mediates the hormonal control of growth via the epidermal growth factor (EGF) receptor. Indeed, we have shown that estrogen-stimulated growth is preceded by an increase in TGFalpha mRNA in the pituitary while, bromergocryptine mediated growth inhibition is preceded by a decrease in TGFalpha mRNA. Our proposal is to enlarge upon these studies. Specifically, we propose to investigate the sites of TGFalpha expression in the pituitary and the modulation of its expression by estrogens and dopamine agonists using in situ hybridization. We also propose to develop transgenic mice in which TGFalpha overexpression is targeted to the lactotroph using the segments of the prolactin promoter which mediate- differing levels of tissue specific expression. These later studies will show whether TGFalpha stimulates lactotroph hyperplasia and hyperfunction. Finally, we have shown that TGFalpha expression is upregulated by phorbol esters and EGF. We have cloned 14 kb of the 5'-flanking region of the human TGFalpha gene of which a 1 kb proximal segment is capable of driving the expression of the luciferase reporter gene in MDA468 cells (human breast carcinoma cells). The 5'-promoter region of the TGFalpha gene is unusual in that it is G-C rich and does not contain typical TPA, EGF or estrogen response elements. On the other hand, it has striking similarity to the EGF receptor gene, which, in our systems, is coordinately regulated with the gene for its ligand, TGFalpha. We propose that these two genes use similar elements (cis- and trans-) to control their expression. Based on the structure of these genes, we believe these elements are distinct from the currently well characterized elements in other genes, raising the potential for the characterization of a novel transcription regulatory system. We plan to characterize the cis-acting elements in the TGFalpha gene that mediate phorbol ester and EGF responsiveness and to isolate and clone the proteins that interact with these elements. Together, the proposed studies will provide insight into the physiological role of TGFalpha in lactotroph, and form the basis for the understanding of its role and controlling mechanisms in other tissues.