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，因素和相关的信号转导途径是未知的。PI发现，生长中的盘基骨柱细胞分泌一种名为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，是分泌约150 kDa复合物的一部分，与细菌和哺乳动物的功能未知的蛋白质有一些相似之处。与野生型细胞相比，无aprA细胞增殖更快，而过表达aprA细胞增殖更慢。此外，将免疫沉淀的AprA添加到细胞中可以减缓细胞的增殖。我提出了三个具体目标来阐明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大约150 kDa的因子是单独含有AprA还是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，或者是抑制增殖的不同途径的一部分。第三，我们将确定该因子生长抑制作用所需的下游成分。在初步筛选中，我们发现了四种慢增殖AprA过表达表型的抑制因子；其中一种编码一种与CLN2相似的蛋白质，CLN2是一种与幼年神经细胞样脂褐质病、低分化肿瘤和心脏肥厚有关的基因。我们将使抑制基因无效，并确定它们是AprA信号转导途径的一部分，还是抑制增殖的不同机制的一部分。我们对aprA突变体和aprA蛋白的鉴定为应用分子和遗传分析细胞外因子抑制细胞增殖的机制开辟了道路。我们预计这些研究将有助于理解多细胞生物中正常组织和肿瘤生长是如何被调节的，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.