Ligand-Receptor Interactions in the TGF-beta superfamily

描述（由申请人提供）：tgf β亚型（beta1、beta2和beta3）是25kda二硫连接的同型二聚体，可调节细胞增殖、细胞分化和细胞外基质蛋白的表达。TGFbeta以其肿瘤抑制活性而闻名，虽然这种活性的丧失会导致某些遗传性结肠癌和胰腺癌，但在大多数癌症中，包括乳腺癌，TGFbeta信号通路保持完整。这通常会产生不良影响，因为tgf β的促瘤活性，包括其刺激免疫抑制和内皮细胞向间质转化的能力，保持不变，但由于视网膜母细胞瘤基因产物（pRB）失活或生长刺激基因（如c-myc）的表达，其生长抑制活性丧失。TGFbeta的三种异构体具有71 - 79%的序列同一性，并通过一对结构相似的单通道跨膜受体TRI和TRII发出信号。然而，同种异构体在体内发挥着不同的作用，如同种异构体特异性-/-缺失小鼠的非重叠和致死表型，在组织植物前测定中添加纯化同种异构体引起的反应差异，以及它们在疾病（如乳腺癌）中发挥的相反作用。这些差异的起源尚不清楚，尽管基于先前基于细胞的交联和结构研究，这可能是由于它们结合和组装受体形成信号复合物的方式不同。本提案的第一个主要目标是确定TRI:TRII: tgf - β信号复合物胞外组分的分子结构。这将提供有关tgfβ受体组装相互依赖性质的基本信息，以及单体相对固定的同种异构体（tgfβ 1和2）与单体不固定的同种异构体（tgfβ 3）的组装差异。该项目的第二个主要组成部分涉及TGFbeta2，它也通过结合并将TRI和TRII结合在一起来发出信号，但它对TRII的结合很弱，并且依赖于第三种细胞表面的TGFbeta2结合蛋白，即β多糖，来诱导其细胞反应。拟议研究的目的是确定TGFbeta共受体β多糖的内啡肽样结构域促进TGFbeta2与TRII结合的机制的结构基础。这将提供第一个例子，如何在家族中的一个共受体的功能，以选择性地提高细胞对一个特定的配体异构体的敏感性。从这些研究中获得的信息将用于产生突变的tgfbeta，以测试在两种不同的细胞系统中，受体结合方式的同种异构体之间的差异是否确实是其生物活性差异的基础。

DESCRIPTION (provided by applicant): TGFbeta isoforms (beta1, beta2, and beta3) are 25 kDa disulfide-linked homodimers that regulate cell proliferation, cell differentiation, and expression of extracellular matrix proteins. TGFbetas 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 TGFbeta signaling pathway remains intact. This usually has adverse effects, since the tumor promoting activities of TGFbeta, 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 TGFbeta share 71 - 79 % sequence identity and signal through a pair of structurally similar single-pass trans-membrane 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 ex-plant 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 cross-linking 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:TGFbeta signaling complex. This will provide fundamental information concerning the inter-dependent nature of TGFbeta 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 (TGFbeta3). The second major component of this project concerns TGFbeta2, 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 TGFbeta 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 TGFbeta co-receptor betaglycan facilitates binding of TGFbeta2 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 TGFbetas, 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.