Regulation of Follistatin Expression by Activin

描述（由申请人提供）：本研究计划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。激活素是多种组织和细胞功能的广泛表达的多效调节剂，包括垂体前叶促性腺激素产生FSH的差异。因此，激活素的作用必然受到多种功能失活或拮抗机制的精确控制。卵泡抑素是分泌的激活素结合糖蛋白，在细胞外调节激活素在大多数组织中的生物利用度。虽然最初被确定为抑制fsh的性腺液成分，但此后的大量研究证明，卵泡抑素存在于许多组织中，包括促性腺激素和垂体前叶的其他细胞类型。激活素是促卵泡抑素表达最有效的诱导剂之一，现在推测，许多已证实的促卵泡抑素的作用反映了它们对激活素和其他tgf - β家族成员生物活性的局部自分泌/旁分泌影响。卵泡抑素缺失的小鼠表现出许多胚胎缺陷，并在出生后不久死亡，这证明了卵泡抑素在平衡激活素的多种作用方面的重要性。另一方面，卵泡抑素过表达与不育有关，因为性腺和垂体水平的功能破坏。在垂体前叶，卵泡抑素的诱导表达建立了一个反馈回路和激活素自我调节进一步信号的机制。本研究的重点是阐明促性腺激素中卵泡抑素基因表达调控的机制。我们已经获得了强有力的证据，证明在促性腺激素衍生的alpha -1和LBetaT2细胞中，大鼠卵泡抑素基因的第一个内含子中的元件通过Smad信号介导激活素对该基因的转录作用。我们建议使用互补的方法来精确定义位于大鼠卵泡抑素基因第一个内含子中的激活素响应区域的元件，表征与Smad3和Smad4一起介导激活素这些作用的促性腺衍生因子，最后确定这些因子作为激活素这种作用的专用介质的功能。本研究还旨在确定激活素在其他垂体和非垂体细胞类型中是否以相同的机制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见解，并为生殖和其他内分泌疾病的管理确定选择性治疗靶点。

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.