ROLE OF BETAGLYCAN IN INHIBIN ANTAGONISM OF ACTIVIN

激活素和某些BMP是TGF-β超家族的成员，调节垂体前叶的FSH产生。它们及其受体在生殖、内分泌和其他系统中也具有多种内分泌、旁分泌和自分泌作用，并在发育和病理生理过程中发挥关键作用。抑制素对抗激活素的一些但不是全部作用，并且对于存活至关重要，如患有性腺和肾上腺肿瘤以及肝坏死的α-抑制素缺失小鼠的致死表型所示。施加 在细胞效应中，激活素（β-β二聚体）结合其II型受体丝氨酸激酶（ActRII或ActRIIB），然后募集I型受体丝氨酸激酶（ALK 4）以形成启动下游信号传导的活性复合物。抑制素（α-β二聚体）与激活素竞争结合ActRII，但抑制素/ActRII复合物不募集ALK 4或促进信号传导。抑制素是激活素的有效功能性拮抗剂，但与激活素相比，抑制素对ActRII的亲和力相对较低，这与简单的竞争模型不一致。因此，寻找其他组分，并且在过去的资助期内，我们鉴定了β聚糖（TGF-β III型受体）作为高亲和力的β受体结合蛋白（共受体），其促进β受体结合ActRII，从而大大增加β受体结合蛋白拮抗激活素信号传导的效力。在模型系统中，我们已经证明，Escherubin可以拮抗一些BMP的反应。在目标I下，这些发现将被扩展到测试BMPs是否拮抗BMPs对垂体细胞的作用。我们将继续表征BMPRII、β聚糖和II型受体ActRII、ActRIIB和BMPRII之间的结合相互作用。我们将鉴定β聚糖残基和β聚糖结合所需的区域，并将产生最小化的可溶性β聚糖形式，用于生物化学和结构（与项目II）研究。确定这些蛋白质的关键相互作用表面和区域将有助于设计 用于调节Escherichia coli应答的策略。目的II提出阻断betaglycan或破坏其在包括垂体促性腺激素在内的垂体素反应细胞类型中的表达。在体外和体内实验将测试β聚糖作为一个专性介体的β受体结合蛋白的作用的重要性。最后，在目标III下，我们将寻找额外的Escherichin共受体。我们和其他人有证据表明，存在多个结合蛋白，包括可能的变种betaglycan，我们建议的特点。这些研究将提高我们对Bisobin作用机制的理解，并将有助于确定控制生育和管理生殖疾病的目标。

Activins and certain BMPs are members of the TGF-beta superfamily that regulate FSH production by the anterior pituitary. They and their receptors also have diverse endocrine, paracrine, and autocrine actions throughout the reproductive, endocrine and other systems and play key roles in development and in pathophysiologic processes. Inhibins oppose some, but not all actions of activin and are crucial for survival as illustrated by the lethal phenotype of inhibin alpha null mice, which suffer gonadal and adrenal tumors and liver necrosis. To exert cellular effects, activins (beta-beta dimers) bind their type II receptor serine kinases (ActRII or ActRIIB) and then recruit the type I receptor serine kinase (ALK4) to form active complexes that initiate downstream signaling. Inhibins (alpha-beta dimers) compete with activins for binding to ActRII but the inhibin/ActRII complexes do not recruit ALK4 or promote signaling. Inhibins are potent functional antagonists of activin yet the relatively low affinity of inhibins compared to activin for ActRII was not in keeping with a simple competition model. Thus other components were sought and during the past grant period we identified betaglycan (TGF-beta type III receptor) as a high affinity inhibin binding protein (co-receptor) that facilitates inhibin binding to ActRII and, thereby, greatly increases the potency of inhibin to antagonize activin signaling. In model systems we have demonstrated that inhibin can antagonize responses to some BMPs. Under Aim I, these findings will be extended to test if inhibins antagonize the effects of BMPs on pituitary cells. We will continue to characterize the binding interactions between inhibins, betaglycan, and the type II receptors, ActRII, ActRIIB and BMPRII. We will identify the betaglycan residues and regions required for inhibin binding and will produce minimized soluble betaglycan forms that will be used for biochemical and structural (with Project II) studies. Identification of the critical interactive surfaces and regions of these proteins will facilitate efforts to devise strategies for modulating inhibin responses. Aim II proposes to block betaglycan or disrupt its expression in inhibin-responsive cell types including pituitary gonadotropes. In vitro and in vivo experiments will test the importance of betaglycan as an obligate mediator of inhibin actions. Finally, under Aim III we will search for additional inhibin co-receptors. We and others have evidence for the existence of multiple inhibin binding proteins including probable variants of betaglycan, which we propose to characterize. These studies will improve our understanding of the mechanisms of inhibin action and will help identify targets for the control of fertility and management of reproductive disorders.