Early involvement of estrogen-induced pituitary tumor transforming gene and fibroblast growth factor expression in prolactinoma pathogenesis

Pituitary tumors are commonly encountered, and result from clonal expansion of a single mutated cell(1). Hypothalamic hormones, local growth factors a nd circulating sex steroid hormones promote pituitary tumor growth and expa nsion into large invasive tumors(2). Estrogen acting directly through its r eceptor and by stimulation of fibroblast growth factor regulates prolactin synthesis and secretion(3-4). Fibroblast growth factor-2 (bFGF) modulates a ngiogenesis, tumor formation and progression in many tissues, including the anterior pituitary(5-8). A pituitary tumor-derived transforming gene (PTTG ) has been isolated, which is tumorigenic in vivo, regulates bFGF secretion , and inhibits chromatid separation(9-11). The human PTTG family consists o f at least three homologous genes, of which PTTG1 is located on chromosome 5q33(12) and is expressed at low levels in most normal human tissues but is highly expressed in malignant human cell lines and in pituitary tumors(13) . We report here that pituitary pttg is regulated in vivo and in vitro by e strogen. Maximal induction of rat pituitary pttg mRNA in vivo occurred earl y in pituitary transformation (normal cell to hypertrophic/hyperplastic cel l), coincident with bFGF and vascular endothelial growth factor induction a nd pituitary angiogenesis. We also demonstrate that pttg expression is indu ced by bFGF, and show concordant pttg and bFGF expression in experimental a nd human pituitary adenomas. As bFGF and estrogen both induce pttg, and ptt g expression coincides with the early lactotrophic hyperplastic response, a ngiogenesis and prolactinoma development, we propose a previously unknown p aracrine growth factor-mediated mechanism for pituitary tumor pathogenesis and potentially other estrogen-regulated tumors.