In vivo functions of possible tumor suppressor Dab2

描述(申请人提供)：DISABLED-2(DAB2)基因被认为是一种肿瘤抑制基因，因为它在人类卵巢癌和乳腺癌中普遍下调，过度表达可以抑制肿瘤的生长。然而，尚未在人类癌症中检测到DAB2基因的突变，而且DAB2在正常细胞中的真实作用尚不清楚。为了确定DAB2在正常细胞中的功能机制，我们一直在研究DAB2蛋白的定位、磷酸化和相互作用，并确定DAB2在小鼠发育过程中的功能。DAB2以P96和P67两种蛋白形式表达。初步研究表明，P96DAB2蛋白被MAP激酶磷酸化，定位于包被网状蛋白的凹坑，并与参与内吞作用的非肌肉肌球蛋白结合。P96DAB2还与脂蛋白受体的胞浆尾巴相关。事实上，我们的缺乏DAB2的条件性基因敲除小鼠表现出与缺乏脂蛋白受体megalin的小鼠相似的肾脏缺陷。因此，我们假设DAB2正常地调节超大蛋白流量。DAB2基因在植入后早期发育过程中还有另一个重要功能。DAB2突变胚胎的胚外内脏内胚层存在缺陷。这种表型表明，转化生长因子β家族成员Nodal的信号转导减少。我们认为DAB2至少有两个功能：一个在信号传递中，另一个在受体交通中。这些功能可以是链接的，也可以是分开的。我们将测试胚胎和肾脏缺陷是否确实分别是由于信号和流量的减少，以及DAB2的p96和p67形式是否具有独立或多余的作用。我们将研究DAB2调节交通的分子机制，特别是肌球蛋白VI的作用。我们将研究DAB2如何在一些细胞中调节Nodal/TGFbeta信号，而不是在其他细胞中。我们还将研究DAB2磷酸化在调节这些反应中的意义。这些研究将为深入了解DAB2的分子作用机制以及单个基因在受体运输和信号转导中的作用提供依据。

DESCRIPTION (provided by applicant): The Disabled-2 (Dab2) gene has been proposed to function as a tumor suppressor because it is commonly down-regulated in human ovarian and mammary carcinomas and over-expression can inhibit carcinoma growth. However, mutations in the Dab2 gene have not been detected in human cancers and the true roles of Dab2 in normal cells are unknown. To determine the mechanisms of Dab2 functions in normal cells, we have been investigating Dab2 protein localization, phosphorylation and interactions, and determining the functions of Dab2 during mouse development. Dab2 is expressed in 2 protein forms, p96 and p67. Preliminary studies show that the p96 Dab2 protein is phosphorylated by MAP kinase, localized to clathrin-coated pits and binds to a non-muscle myosin implicated in endocytosis. p96 Dab2 also associates with the cytoplasinic tails of lipoprotein receptors. Indeed, our conditional knockout mice that lack Dab2 show kidney defects similar to those of mice lacking the lipoprotein receptor, megalin. Thus we hypothesize that Dab2 normally regulates megalin traffic. The Dab2 gene has another important function during early post-implantation development. Dab2 mutant embryos have a defect in the extraembryonic visceral endoderm. The phenotype suggests reduced signaling by Nodal, a TGF beta family member. We propose that Dab2 has at least two functions: one in signaling and one in receptor traffic. These functions may be linked or separate. We will test whether the embryonic and kidney defects are indeed due to reduced signaling and traffic, respectively, and whether the p96 and p67 forms of Dab2 have separate or redundant roles. We will investigate the molecular mechanisms whereby Dab2 regulates traffic, especially the role of myosin VI. We will investigate how Dab2 modulates Nodal/TGFbeta signaling in some cells but not others. We will also investigate the significance of Dab2 phosphorylation in regulating these responses. These studies will provide insights into the molecular mechanisms of action of Dab2 and into the role of a single gene in receptor trafficking and signal transduction.