An autocrine repressor of cell proliferation

描述（由申请人提供）：许多细胞，包括一些肿瘤细胞，似乎分泌抑制其增殖的自分泌因子。在大多数情况下，因子和相关的信号转导途径是未知的。PI发现生长中的盘基网柄菌细胞分泌一种名为AprA的蛋白质，用于自分泌增殖抑制因子。AprA是一种60 kDa的蛋白质，是一种分泌的约150 kDa复合物的一部分，与细菌和哺乳动物的未知功能蛋白质有一定的相似性。与野生型细胞相比，aprA缺失细胞增殖更快，而AprA过表达细胞增殖更慢。此外，向细胞中加入免疫沉淀的AprA会减缓它们的增殖。我提出了三个具体的目标来阐明AprA调节细胞增殖的机制。首先，我们将通过纯化该因子并鉴定其组分来确定约150 kDa的因子是否含有单独的AprA或AprA加上其他因子。其次，我们将确定该因子的候选受体是否感知并结合该因子，或者是否是抑制增殖的不同途径的一部分。第三，我们将确定该因子的生长抑制作用所需的下游组分。在初步筛选中，我们确定了四个抑制剂的缓慢增殖AprA过表达表型;一个编码的蛋白质与CLN 2，一个基因牵连在青少年神经元蜡样质脂褐质沉积症，分化不良的肿瘤，和心脏肥大的相似性。我们将使抑制基因无效，并确定它们是否是AprA信号转导途径的一部分，或者是抑制增殖的不同机制的一部分。我们的鉴定的aprA突变体和AprA蛋白开辟了分子和遗传分析的机制，细胞外因子可以抑制增殖的应用。我们预计，这些研究将有助于了解正常组织和肿瘤生长在多细胞生物中是如何调节的，并可能有助于找到抑制肿瘤细胞增殖的新方法。

DESCRIPTION (provided by applicant): Many cells, including some tumor cells, appear to secrete autocrine factors that repress their proliferation. In most cases the factors and associated signal transduction pathways are unknown. The PI has found that growing Dictyostelium cells secrete a protein called AprA for autocrine proliferation repressor. AprA is a 60 kDa protein, is part of a secreted approximately 150 kDa complex, and has some similarity to bacterial and mammalian proteins of unknown function. Compared to wild-type cells, aprA null cells proliferate faster while AprA overexpressing cells proliferate slower. Furthermore, adding immunoprecipitated AprA to cells slows their proliferation. I propose three specific aims to elucidate the mechanisms by which AprA regulates cell proliferation. First, we will determine if the approximately 150 kDa factor contains AprA alone or AprA plus additional factors, by purifying this factor and identifying its components. Second, we will determine if our candidate receptor for this factor senses and binds this factor, or is part of a different pathway that inhibits proliferation. Third, we will identify downstream components that are required for the growth inhibitory action of this factor. In preliminary screens, we identified four suppressors of the slow-proliferation AprA overexpressor phenotype; one encodes a protein with similarity to CLN2, a gene implicated in juvenile neuronal ceroid lipofuscinosis, poorly differentiated tumors, and cardiac hypertrophy. We will make nulls of suppressor genes and determine if they are part of the AprA signal transduction pathway, or are part of a different mechanism that represses proliferation. Our identification of the aprA mutant and AprA protein has opened the way for the application of molecular and genetic analysis to the mechanism by which extracellular factors can inhibit proliferation. We anticipate that these studies will assist in understanding both how normal tissue and tumor growth are regulated in multicellular organisms, and may help lead to novel ways to repress tumor cell proliferation.