TGF-beta receptor sumoylation and cell behavior

描述（由申请人提供）：自分泌TGF-β信号传导在癌症进展中起关键作用，从而在早期癌发生中充当肿瘤抑制因子，并刺激侵袭导致转移。大多数癌对TGF-β的反应失调，导致对TGF-β的抗增殖反应失活。在某些情况下，这种失调与I型或II型TGF-β受体的突变有关。SUMO化，即泛素样SUMO蛋白的共价连接，是一种新兴的蛋白质翻译后修饰。类小泛素化的作用通常是不可预测的，似乎取决于靶蛋白。SUMO相互作用蛋白的可能募集可能导致靶蛋白的蛋白复合物形成和功能特性的变化。类小泛素化主要表征为参与核功能的转录因子和蛋白质的修饰，而细胞表面受体的类小泛素化尚未报道。我们最近发现I型TGF-β受体TbRI被sumoylated，使我们假设sumoylation调节该受体的功能，从而调节TGF-β信号传导和细胞对TGF-β的反应。在确定了TbRI中的小泛素化位点后，我们还发现TbRI中的一个点突变（已发现与转移性乳腺癌相关）使TbRI缺乏小泛素化。这导致了TbRI的类小泛素化影响自分泌TGF-β信号传导并且是癌的侵袭行为的决定因素的假设。我们提出了三个目标来定义TbRI类小泛素化的分子机制及其在细胞对TGF-β的反应和癌细胞在体内的行为中的作用。目的1将描述TbRI的SUMO化机制，包括寻找负责E3 SUMO连接酶。目的2研究TbRI类小泛素化对Smad和非Smad信号通路的影响以及TGF-b对细胞增殖和侵袭的影响。该目的还应定义“转移相关”TbRI突变体、野生型TbRI和类小泛素化缺陷型TbRI点突变体在对TGF-β的信号传导和细胞行为应答中的功能差异。最后，目标3将定义TbRI类小泛素化和“转移相关”TbRI点突变对癌细胞行为和体内癌症进展的影响。拟议的研究应提供一个基础的TGF-β受体类小泛素化的机制，其在细胞对TGF-β的反应和在癌细胞行为和癌症进展的特点。

DESCRIPTION (provided by applicant): Autocrine TGF-beta signaling plays key roles in cancer progression, thereby acting as tumor suppressor in early carcinogenesis, and in stimulating invasion leading to metastasis. Most carcinomas have a deregulated response to TGF-beta, leading to inactivation of the antiproliferative response to TGF- beta. In some cases this deregulation is associated with mutations in the type I or type II TGF-beta receptors. Sumoylation, i.e. the covalent attachment of a ubiquitin-like SUMO protein, is an emerging posttranslational modification of various proteins. The role of sumoylation is often unpredictable and seems to depend on the target protein. Possible recruitment of SUMO-interacting proteins may lead to changes in the protein complex formation and functional properties of the target protein. Sumoylation is largely characterized as a modification of transcription factors and proteins involved in nuclear functions, and sumoylation of cell surface receptors has not been reported. We recently discovered that the type I TGF- beta receptor, TbRI, is sumoylated, making us hypothesize that sumoylation regulates the function of this receptor, and consequently TGF-beta signaling and the cell's response to TGF-beta. After identifying the sumoylation site in TbRI, we also found that a point mutation in TbRI, which has been found in association with metastatic breast cancer, confers a lack of sumoylation to TbRI. This leads to the hypothesis that sumoylation of the TbRI affects autocrine TGF-beta signaling and is a determinant of the invasive behavior of carcinomas. We propose three aims to define the molecular mechanism of TbRI sumoylation and its role in the cellular responses to TGF-b and the behavior of cancer cells in vivo. Aim 1 will characterize the mechanism of sumoylation of TbRI, including a search to identify the responsible E3 SUMO ligase. Aim 2 will examine the effect of TbRI sumoylation on Smad and non-Smad signaling responses and the cell's proliferation and invasion responses to TGF-b. This Aim should also define functional differences between the "metastasis- associated" TbRI mutant, wild-type TbRI and a sumoylation-deficient TbRI point mutant in the signaling and cell behavior responses to TGF-b. Finally, Aim 3 will define the effect of TbRI sumoylation and of the "metastasis-associated" TbRI point mutation on the behavior of cancer cells and on cancer progression in vivo. The proposed studies should provide a basis for the characterization of the mechanism of the TGF- beta receptor sumoylation, its role in the cell's response to TGF-beta and in cancer cell behavior and cancer progression.