Ligand-Receptor Interactions in the TGF-beta superfamily

TGFp异构体((31，(32，和p3)是25 kDa的二硫键连接的同源二聚体，调节细胞增殖，细胞 细胞外基质蛋白的分化和表达。TGFp最为人所知的是其肿瘤 抑制活性，虽然这种活性的丧失会导致某些形式的结肠和胰腺遗传性疾病 癌症，在大多数癌症中，包括乳腺癌，TGFp信号通路保持完整。这 通常有不良影响，因为TGFP的促肿瘤活性，包括它的刺激能力 免疫抑制和内皮细胞向间充质细胞的转变保持完好，但其生长抑制 由于视网膜母细胞瘤基因产物(PRB)的失活或生长的表达而失去活性 刺激基因，如c-myc。TGFp的三种异构体具有71-79%的序列同源性和 通过一对结构相似的单程跨膜受体TRI和TRII传递信号。 然而，异构体在体内发挥着不同的作用，如不重叠和致死的表型所表明的那样 在异构体特异性/缺失小鼠中，通过添加纯化的异构体引起的反应差异 组织外植体分析，以及它们在乳腺癌等疾病中扮演的相反角色。它们的起源 这些差异的原因还不清楚，尽管基于以前的基于细胞的交联和结构 研究表明，这可能是由于它们与受体结合并将其组装成 信号复杂。这项提议的第一个主要目标是定义 TRI：TRII：TGFp信号复合体的胞外成分。这将提供基本信息 关于TGFp受体组装的相互依赖性以及TGFp受体组装的不同 单体相对固定的异构体(TGFPS 1和2)与其 单体不固定(TGFpS)。该项目的第二个主要组成部分涉及TGFp2，它还 通过结合和结合TRI和TRII来传递信号，但它对TRI的结合很弱，而且是依赖的 在第三个细胞表面，TGFp结合蛋白，称为Betaglycan，诱导其细胞反应。这个 拟议研究的目标是确定潜在的结构基础 TGFp共受体β-聚糖的endoglin样结构域促进了TGFp2与TRII的结合。这将是 提供第一个例子，说明家庭中的一个辅助受体如何发挥作用，选择性地增强 细胞对特定配基异构体的敏感性。然后将使用从这些研究中获得的信息 产生突变的转化生长因子，以测试不同亚型之间受体方式的差异 结合确实强调了它们使用两种不同的基于细胞的系统在生物活性上的差异。

TGFp isoforms ((31, (32, and p3) are 25 kDa disulfide-linked homodimers that regulate cell proliferation, cell differentiation, and expression of extracellular matrix proteins. TGFps are best known for their tumor suppressor activity, and while loss of this activity leads to certain hereditary forms of colon and pancreatic cancer, in most cancers, including those of.the breast, the TGFp signaling pathway remains intact. This usually has adverse effects since the tumor promoting activities of TGFp, including its ability to stimulate immune suppression and endothelial-to-mesenchymal transitions, remain intact, yet its growth inhibitory activity is lost, due to either inactivation of the retinoblastoma gene product (pRB) or expression of growth stimulatory genes, such as c-myc. The three isoforms of TGFp share 71 - 79 % sequence identity and signal through a pair of structurally similar single-pass transmembrane receptors known as TRI and TRII. The isoforms nevertheless fufill distinct roles in vivo as shown by the non-overlapping and lethal phenotypes of the isoform specific -/- null mice, by differences in response induced by the addition of purified isoforms in tissue explant assays, and by the opposing roles they play in diseases, such as breast cancer. The origins of these differences are not understood, although based on previous cell-based crosslinking and structural studies, it might be due to differences in the manner by which they bind and assemble their receptors into a signaling complex. The first major objective of this proposal is to define the molecular architecture of the extracellular component of the TRI:TRII:TGFp signaling complex. This will provide fundamental information concerning the interdependent nature of TGFp receptor assembly, as well as how assembly differs for the isoforms whose monomers are fixed relative to one another (TGFps 1 and 2) compared to those whose monomers are not fixed (TGFpS). The second major component of this project concerns TGFp2, which also signals by binding and bringing together TRI and TRII, but which binds TRII weakly, and which is dependent upon a third cell surface TGFp binding protein, known as betaglycan, to induce its cellular responses. The objective of the proposed studies is to determine the structural basis underlying the mechanism by which the endoglin-like domain of the TGFp co-receptor betaglycan facilitates binding of TGFp2 to TRII. This will provide the first example of how one of the co-receptors in the family functions to selectively enhance the sensitivity of cells to a particular ligand isoform. The information derived from these studies will then be used to generate mutant TGFps to test whether differences among the isoforms in their manner of receptor binding indeed underlie their differences in biological activity using two different cell-based systems.