Lysophosphatidic Acid in Oncogenesis

修订摘要 溶血磷脂酸（LPA），一种天然存在的溶血磷脂，是至少 G蛋白偶联受体（LPA 15）。LPA 13受体是内皮细胞的成员。 细胞分化基因（Edg）家族，并与G蛋白的Gi、Gq和G12/13亚基偶联， 激活一系列细胞内信号级联，导致细胞骨架重排，细胞 增殖、生存和迁移。Edg LPA受体的过表达和上调 通过LysoPLD/autotaxin（AIX）产生LPA的异常是在各种疾病中发现的常见异常。 人类癌症然而，LPA致癌作用的研究由于缺乏足够的信息来源而受到阻碍。 体内证据或动物模型显示LPA信号参与肿瘤发展。 最近，嘌呤能受体家族的p2 γ 9/GPR 23/LPA 4和相关的 GPR 92/LPA 5被鉴定为新的LPA受体。这两种受体在结构上 远离Edg LPA 1.. Gq、GI 2/13和Gs亚基。的 LPA 4和LPA 5受体的生物学功能，特别是它们在癌症中的作用， 以前研究过。我们最近通过在小鼠中进行靶向缺失来破坏Ipa 4基因。 虽然LPA 4不是胚胎发育和生育所必需的，但我们观察到， 在Ipa 4突变小鼠中自发性肿瘤的发展显著增加。肿瘤 包括恶性淋巴瘤、肺腺癌、高度恶性肉瘤、平滑肌肉瘤 浆细胞瘤和毛母质瘤。在这些小鼠中发现的广泛的肿瘤不仅 提供了肿瘤发生中异常LPA信号传导的直接证据， LPA 4作为肿瘤抑制因子的可能性。我们的初步结果进一步表明， LPA 4的缺乏使细胞对LPA诱导的细胞运动和特异性细胞内 途径。因此，我们假设，与Edg LPA受体相反，LPA 4 负调控特定LPA信号通路和LPA的致癌活性。作为 因此，LPA 4的缺乏使小鼠易于发生肿瘤。假设是 通过以下三个具体目标进行测试： 目标1.确定LPA 4在小鼠肿瘤抑制中的作用; 目标二。阐明LPA 4在LPA信号转导中的作用; 目标3。为了评估LPA 4的缺失是否增加小鼠对化学物质的易感性， 癌变 我们将在两个实验室中测定肿瘤的发病率、组织类型和转移率， Aim 1中Ipa 4敲除小鼠的独立品系。我们将利用LPA 4缺陷 细胞和其他敲低或过表达方法来研究生物学特性， LPA 4在LPA信号转导和细胞应答调节中的功能（目的2）。 在目的3中，将通过检查LPA 4的肿瘤抑制功能来进一步探索LPA 4的肿瘤抑制功能。 LPA 4缺失小鼠对化学致癌物的易感性。这些拟议的研究将 建立LPA 4在肿瘤抑制中的作用，并可能导致新的抗癌药物的鉴定。 目标的

Revised Abstract Lysophosphatidic acid (LPA), a naturally occurring lysophospholipid, is a ligand of at least five G protein-coupled receptors (LPA15). The LPA13 receptors are members of the endothelial cell differentiation gene (Edg) family and couple to Gi, Gq, and G12/13 subunits of G proteins to activate an array of intracellular signaling cascades, leading to cytoskeleton rearrangement, cell proliferation, survival, and migration. Overexpression of the Edg LPA receptors and upregulation of LPA production via LysoPLD/autotaxin (AIX) are common abnormalities found in various human cancers. However, studies of oncogenic roles of LPA have been hampered by lack of in vivo evidence or an animal model to show involvement of LPA signals in tumor development. Recently, p2y9/GPR23/LPA4 of the purinergic receptor family and a related GPR92/LPA5 are identified as novel LPA receptors. These two receptors are structurally distant from the Edg LPA1..3 receptors and couple to Gq, GI 2/13 and Gs subunits. The biological functions of LPA4 and LPA5 receptors, particularly their roles in cancer have not been previously studied. We recently disrupted the Ipa4 gene by targeted deletion in mice. Although the LPA4 is not required for embryonic development and fertility, we observed a dramatic increase in development of spontaneous tumors in Ipa4 mutant mice. The tumors include malignant lymphoma, lung adenocarcinoma, high-grade sarcoma, leiomyosarcoma, plasmacytoma and pilomatrixoma. The wide spectrum of tumors found in these mice not only provides direct evidence for aberrant LPA signaling in tumorigenesis but also raises the possibility that LPA4 acts as a tumor suppressor. Our preliminary results further suggest that lack of LPA4 sensitizes cells to LPA-induced cell motility and activation of specific intracellular pathways. We therefore hypothesize that, in contrast to the Edg LPA receptors, LPA4 negatively regulates specific LPA signaling pathways and oncogenic activity of LPA. As a result, the lack of LPA4 predisposes mice to tumor development. The hypothesis will be tested through the following three Specific Aims: Aim 1. To determine the role of LPA4 in tumor suppression in mice; Aim 2. To elucidate the functions of LPA4 in LPA signal transduction; Aim 3. To evaluate whether deletion of LPA4 increases susceptibility of mice to chemical carcinogenesis We will determine tumor incidence, histotypes and metastasis rate of tumors in two independent lines of Ipa4 knockout mice in Aim 1. We will take advantage of the LPA4-deficient cells and other knockdown or overexpression approaches to investigate the biological functions of LPA4 in the regulation of LPA signal transduction and cellular responses (Aim 2). In Aim 3, the tumor suppressive function of LPA4 will be further explored by examining the susceptibility of LPA4 null mice to chemical carcinogens. These proposed studies together will establish the role of LPA4 in tumor suppression and may lead to identification of novel anticancer targets.