Regulation of Follistatin Expression by Activin

描述(申请人提供)：本研究提案的主要目的是了解激活素依赖的Smad信号如何导致垂体前叶促性腺激素中卵泡抑素基因的激活。激活素是广泛表达的多种组织和细胞功能的多效性调节因子，包括垂体前叶促性腺激素产生的不同FSH。因此，激活素的活动必然受到多种功能失活或拮抗机制的精确控制。卵泡抑素是一种分泌激活素结合的糖蛋白，其功能是在细胞外调节激活素在大多数组织中的生物利用度。虽然最初被鉴定为性腺液中抑制FSH的成分，但自那以后，许多研究都证明了卵泡抑素在许多组织中的存在，包括促性腺激素和其他类型的垂体前叶细胞。激活素是卵泡抑素表达的最有效的诱导剂之一，现在推测，许多已证实的作用反映了其局部自分泌/旁分泌对激活素生物活性的影响，也可能是对其他转化生长因子-β家族成员的影响。卵泡抑素基因缺失的小鼠表现出许多胚胎缺陷，并在出生后不久死亡，这证明了它们抵消激活素不同影响的行动的重要性。另一方面，卵泡抑素的过度表达与不育症有关，因为性腺和脑垂体水平的功能障碍。在垂体前叶，卵泡抑素的可诱导表达为激活素建立了一个反馈回路和一种自我调节进一步信号的机制。这一建议的重点是阐明促性腺激素中卵泡抑素基因表达的调节机制，该机制知之甚少。我们已经获得了强有力的证据，大鼠卵泡抑素基因第一内含子的元件通过Smad信号介导激活素在促性腺激素来源的αT3-1和LBetaT2细胞中对该基因的转录效应。我们建议使用互补的方法来精确地定义位于大鼠卵泡抑素基因第一内含子中的激活素反应区域的元件，以表征与Smad3和Smad4一起介导激活素的这些效应的促性腺激素衍生因子(S)，并最终确定这些因子作为激活素这一作用的必要介导者的功能。这些研究还旨在确定激活素是否通过相同的机制在其他类型的垂体和非垂体细胞中诱导卵泡抑素的表达。总之，这些研究将为激活素控制促性腺激素中卵泡抑素表达的机制提供重要的见解，并确定用于管理生殖和其他内分泌疾病的选择性治疗靶点。

DESCRIPTION (provided by applicant): The major objective of this research proposal is to gain an understanding of how activin-dependent Smad signaling leads to follistatin gene activation in anterior pituitary gonadotropes. Activins are widely expressed pleiotropic regulators of diverse tissues and cellular functions, including the differential production of FSH from gonadotropes of the anterior pituitary. Thus of necessity, the actions of activins are under the precise control of multiple mechanisms of functional inactivation or antagonism. Follistatins are secreted activin-binding glycoproteins that function extracellularly to modulate the bio-availability of activins in most tissues. Although first identified as FSH-suppressing components of gonadal fluids, numerous studies have since documented the presence of follistatin in many tissues, including gonadotropes and other cell types of the anterior pituitary. Activins are one of the most potent inducers of follistatin expression and it is now presumed that many of the demonstrated actions of follistatins reflect their local autocrine/paracrine influence on the bioactivity of activins and possibly other TGF-Beta family members. As testimony to the importance of their actions to counterbalance the diverse effects of activins, mice null for follistatin exhibit many embryonic defects and die shortly after birth. On the other hand, follistatin over-expression is associated with infertility because of functional disruptions at the level of the gonads and the pituitary. In the anterior pituitary, the inducible expression of follistatin establishes a feedback loop and a mechanism for activin to self-modulate further signaling. The focus of this proposal is to elucidate the poorly understood mechanism underlying the regulation of follistatin gene expression in gonadotropes. We have obtained strong evidence that elements in the fin'st intron of the rat follistatin gene mediate the transcriptional effects of activin, via Smad signaling, on this gene in gonadotrope-derived alphaT3-1 and LBetaT2 cells. We propose to use complementary approaches to define precisely the elements of the activin-responsive region located in the first intron of the rat follistatin gene, to characterize gonadotrope-derived factor(s) that mediate these effects of activin in conjunction with Smad3 and Smad4 and, finally, to determine the function of these factors as obligate mediators of this action of activin. The proposed studies also aim to determine if activin induces follistatin expression by the same mechanism in other pituitary and non-pituitary cell types. Altogether, these studies will provide important insights into the mechanism by which activin controls follistatin expression in gonadotropes and identify selective therapeutic targets for the management of reproductive and other endocrine disorders.