Ligand-Receptor Interactions in the TGF-beta superfamily

TGF β同种型（β 1、β 2和β 3）是25 kDa的二硫键连接的同源二聚体，其调节细胞增殖、细胞凋亡和细胞凋亡。 分化和细胞外基质蛋白的表达。TGF β最为人所知的是它们的肿瘤 抑制活性，而这种活性的丧失导致某些遗传形式的结肠和胰腺癌， 在大多数癌症中，包括乳腺癌，TGF β信号通路保持完整。这 由于TGF β的肿瘤促进活性，包括其刺激肿瘤生长的能力， 免疫抑制和内皮细胞向间充质细胞转化，保持完整，但其生长抑制 由于视网膜母细胞瘤基因产物（pRB）的失活或生长抑制因子的表达， 刺激基因，如c-myc。TGF β的三种同种型共享71 - 79%的序列同一性， 通过一对称为TRI和TRII的结构相似的单程跨膜受体进行信号传导。 然而，这些亚型在体内发挥不同的作用，如非重叠和致死表型所示。 同种型特异性-/-无效小鼠，通过加入纯化的同种型诱导的反应差异， 组织外植体测定，以及它们在疾病中发挥的相反作用，如乳腺癌。起源 尽管基于先前的基于细胞的交联和结构， 研究表明，这可能是由于它们结合和组装受体的方式不同， 信号复合体该提案的第一个主要目标是定义 TRI：TRII：TGF β信号传导复合物的细胞外组分。这将提供基本信息 关于TGF β受体组装的相互依赖性，以及如何组装不同， 与那些单体相对于彼此固定的同种型（TGF β 1和2）相比， 单体不固定（TGF β 5）。该项目的第二个主要组成部分涉及TGF β 2， 通过结合并将TRI和TRII结合在一起来传递信号，但其与TRII的结合较弱，并且依赖于 第三细胞表面TGF β结合蛋白，称为β聚糖，以诱导其细胞反应。的 拟议研究的目的是确定潜在机制的结构基础， TGF β共受体β聚糖的内皮素样结构域促进TGF β 2与TRII的结合。这将 提供了家族中的共受体之一如何起作用以选择性地增强免疫应答的第一个例子。 细胞对特定配体同种型的敏感性。然后将使用从这些研究中获得的信息 产生突变TGF β，以测试同种型之间的差异是否在其受体的方式， 结合实际上是它们使用两种不同的基于细胞的系统的生物活性差异的基础。

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.