Lysophosphatidic Acid in Oncogenesis

修订后的摘要 溶血磷脂酸(LPA)是一种天然存在的溶血磷脂，是至少 5个G蛋白偶联受体(LPA15)。LPA13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亚基偶联以 激活一系列细胞内信号级联，导致细胞骨架重排 扩散、生存和迁徙。EDG LPA受体的过表达及其上调 通过溶血磷脂酶D/自体趋化蛋白(AIX)产生LPA是一种常见的异常 人类癌症。然而，LPA致癌作用的研究因缺乏In而受到阻碍。 显示LPA信号参与肿瘤发展的活体证据或动物模型。 最近，嘌呤能受体家族的p2y9/GPR23/LPA4及其相关基因 GPR92/LPA5为新的LPA受体。这两种受体在结构上 远离EDG LPA1..3受体，与Gq、GI2/13和Gs亚基偶联。这个 LPA4和LPA5受体的生物学功能，特别是它们在癌症中的作用尚未见报道 已经被研究过了。我们最近在小鼠身上通过靶向缺失破坏了IPA4基因。 虽然LPA4不是胚胎发育和生育所必需的，但我们观察到 IPA4突变小鼠自发性肿瘤的发展急剧增加。肿瘤 包括恶性淋巴瘤、肺腺癌、高级别肉瘤、平滑肌肉瘤 浆细胞瘤和毛发粘液瘤。在这些小鼠身上发现的广谱肿瘤不仅 为LPA信号在肿瘤发生中的异常提供了直接证据，但也提高了 LPA4作为肿瘤抑制因子的可能性。我们的初步结果进一步表明， 缺乏LPA4使细胞对LPA诱导的细胞运动和特异性细胞内激活敏感 小路。因此，我们假设，与EDG LPA受体相反，LPA4 负向调节特定的LPA信号通路和LPA的致癌活性。AS 因此，LPA4的缺乏使小鼠更容易发生肿瘤。假设将是 通过以下三个具体目标进行了测试： 目的1.确定LPA4在小鼠肿瘤抑制中的作用； 目的2.阐明LPA4在LPA信号转导中的作用； 目的3.评估LPA4缺失是否会增加小鼠对化学物质的易感性 致癌作用 我们将确定肿瘤的发病率、组织类型和肿瘤的转移率 目标1中独立的IPA4基因敲除小鼠品系。我们将利用LPA4缺陷 细胞和其他击倒或过度表达的方法来研究生物学 LPA4在调节LPA信号转导和细胞反应中的作用(目标2)。 在目标3中，LPA4的肿瘤抑制功能将通过检测 LPA4基因缺失小鼠对化学致癌物的易感性。这些拟议的研究将一起 确定LPA4在肿瘤抑制中的作用并可能导致发现新的抗癌药物 目标。

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.