Signal Transduction Mechanism in differentiation and Development of Follicular Granulosa Cells.

激活素最初是从哺乳动物肝腺中分离出来的，作为垂体细胞分泌FSH的刺激物。发现其一级结构与TGF-β非常相似。近年来的研究证实，mfivin与TGF-β一样，在发育、分化和形态发生等多种生物学反应中具有广泛的功能。本课题的研究重点是阐明激活素信号转导的机制。(1)We在大鼠卵母细胞和牛垂体中发现了一种激活素结合蛋白，该蛋白对激活素具有特异性和高亲和力，并证明它与最初从猪卵巢中获得的FSH分泌抑制剂卵泡抑素相同。我们还证明了卵泡抑素在各种系统中对激活素活性发挥中和作用。卵泡抑素对激活素作用的这些抑制作用可以通过我们发现卵泡抑素直接与激活素结合形成无活性复合物来解释。卵泡抑素很可能在调节激活素的各种作用中起重要作用。（2）用~（131）I-激活素（activin）亲和标记法显示培养的大鼠颗粒细胞分泌的卵泡抑素与细胞表面结合<125>。它与细胞表面蛋白聚糖的硫酸乙酰肝素侧链结合。细胞结合的卵泡抑素可以捕获基质中和细胞表面的激活素，并重新调节激活素的各种作用。(3)An用亲和层析法从小鼠Friend白血病细胞F5-5、人红白血病细胞K562和小鼠EC细胞P19的细胞膜组分中分离出活化素受体蛋白。SDS-PAGE显示一条70 kDa的条带。前18个残基的氨基酸序列显示，纯化的受体是激活素受体家族的成员。

Activin was originally isolated from mammalian ganads as a stimulator for FSH secretion by pituitary cells. the primary structures was found to be very similar to TGF-beta. Recent studies have verified that, like TGF-beta, mfivin has vadous fimctions in various biological reactions including development, differentiation and morphogenesis. In this project, we focused on elucidation of the mechanism for activin signal msduction.(1)We found in rat ovaly and bovine pituitary an activin-binding protein with a specific and high affinity for activin, and proved that it was identical to follistatin, which was initially obtained from pig ovary as an FSHsecretion suppressor. We also demonstrated that follistatin exerts a neutralizing effect on activin activity in various systems. These inhibitory effects of follistatin on activin actions can be explained by our finding that folhstatin binds directly to activin to form an inactive complex. Follistatin very likely plays a significant role in the regulation of various actions of activin. (2)Follistatin secreted by cultured rat granulosa cells was shown to associate with cell surface by affinity labeling with ^<125>I-activin. It bound to the heparan sulfate side chains of proteoglycans on the cell surface. Cell-bound follistatin may capture activin in the matrix and at the cell surface and regurate the various actions of activin. (3)An activin receptor protein was isolated by affinity chromatography on an activin-immobilizedcolumn from membrane fractions of several cell cultures including mouse Friend leukemia cell F5-5, human erythroleukemia cell K562 and mouse EC cell P19. SDS-PAGE of the prepretion showed one band of 70 kDa. The amino acid sequence of the first 18 residues revealed that the purified receptor is a member of the activin receptor family.