Role of a Novel Lysophospholipase in Tumorigenesis

描述（由申请人提供）：已知磷脂和溶血磷脂可作为调节细胞增殖和存活信号传导途径的脂质有丝分裂原。这些脂质的水平由其各自的脂肪酶严格调节，因此，这些酶的表达和活性对于细胞内稳态至关重要。我们已经克隆了一个cDNA，编码一种新的推定溶血磷脂酶。鉴于其预测的分子量为34 kDa，我们将其命名为LPL 34（溶血磷脂酶34）。初步结果表明，LPL 34含有脂肪酶活性。我们的初步结果还表明，LPL 34 mRNA在正常结肠粘膜中高度表达，但在已建立的结肠癌细胞系中不存在或减少。与其匹配的正常组织相比，LPL 34 mRNA表达在63%（24/38）的原发性结肠癌中也丢失或减少。使用纯化的LPL 34蛋白，我们已经产生了两种高质量的LPL 34抗体。使用这些抗体的蛋白质印迹和免疫组织化学分析表明，在所有测试的原发性结肠肿瘤中，LPL 34蛋白表达也显著降低。与这些结果一致，在缺乏内源性LPL 34的癌细胞中表达外源性LPL 34导致生长抑制，表明LPL 34似乎是新的肿瘤抑制因子。为了研究LPL 34改变在结肠肿瘤发生中的相关性，我们将检测匹配的原发性结肠正常和肿瘤标本中的LPL 34蛋白表达状态，并将LPL 34表达与各种临床病理学参数相关联。将研究负责结肠肿瘤中LPL 34下调的分子机制，还将确定LPL 34的脂肪酶活性在细胞生长抑制中的作用。为了进一步了解LPL 34在细胞生长控制中的生理功能，我们将启动研究以鉴定和研究其潜在的脂质底物和相互作用蛋白。为了阐明LPL 34在胃肠道恶性肿瘤中的作用，我们提出在转基因小鼠的胃肠道中产生LPL 34的可诱导的条件性缺失。这些研究的结果将提供关于（1）LPL 34作为诊断/预后标志物的价值，（2）这种新型溶血磷脂酶在正常细胞生长中作用的分子机制和（3）其在结肠癌发展中的作用的重要信息。 公共卫生相关性：已知磷脂和溶血磷脂充当调节细胞增殖和存活信号传导途径的脂质有丝分裂原。这些脂质的水平由其各自的脂肪酶严格调节，因此，这些酶的表达和活性对于细胞内稳态至关重要。我们已经克隆了一个cDNA，编码一种新的推定的lysophosphoplipase，命名为LPL 34。我们的初步结果表明，LPL 34含有脂肪酶活性，可能参与结肠癌的发展。我们提出了三个具体的目标来研究这种新的溶血磷脂酶。这些研究的结果将提供关于（1）LPL 34作为诊断/预后标志物的价值，（2）这种新型溶血磷脂酶在正常细胞生长中作用的分子机制和（3）其在结肠癌发展中的作用的重要信息。

DESCRIPTION (provided by applicant): Phospholipids and lysophospholipids are known to act as lipid mitogens that regulate cell proliferation and survival signaling pathways. The levels of these lipids are tightly regulated by their respective lipases and thus, the expression and activity of these enzymes is critical for cellular homeostasis. We have cloned a cDNA that encodes a novel putative lysophospholipase. In view of its predicted molecular mass of 34 kDa, we have named it LPL34 (Lysophospholipase 34). Preliminary results suggest that LPL34 contains lipase activity. Our preliminary results also show that LPL34 mRNA is highly expressed in normal colon mucosa but absent or reduced in established colon cancer cell lines. LPL34 mRNA expression is also lost or reduced in 63% (24/38) of primary colon cancers when compared to their matching normal tissues. Using purified LPL34 protein, we have generated two high quality LPL34 antibodies. Western blot and immunohistochemistry analyses using these antibodies demonstrate that LPL34 protein expression is also significantly reduced in all primary colon tumors tested. Consistent with these results, expression of exogenous LPL34 in cancer cells lacking endogenous LPL34 results in growth inhibition suggesting that LPL34 appears to be a novel tumor suppressor. To investigate the relevance of LPL34 alterations in colon tumoriogenesis, we will examine LPL34 protein expression status in matching primary colon normal and tumor specimens and correlate LPL34 expression with various clinicapathological parameters. The molecular mechanism(s) responsible for LPL34 down-regulation in colon tumor will be investigated and the role of lipase activity of LPL34 in cellular growth suppression will also be determined. To further understand the physiological function(s) of LPL34 in cell growth control, we will initiate studies to identify and study its potential lipid substrates and interacting proteins. To delineate the role of LPL34 in the GI malignancies, we propose to generate inducible conditional deletion of LPL34 in the GI tract of transgenic mice. The outcome of these studies will provide important information about (1) the value of LPL34 as diagnostic/prognostic marker, (2) the molecular mechanism(s) of action of this novel lysophospholipase in normal cell growth and (3) its contribution in colon cancer development. PUBLIC HEALTH RELEVANCE: Phospholipids and lysophospholipids are known to act as lipid mitogens that regulate cell proliferation and survival signaling pathways. The levels of these lipids are tightly regulated by their respective lipases and thus, the expression and activity of these enzymes is critical for cellular homeostasis. We have cloned a cDNA that encodes a novel putative lysophospohlipase, named LPL34. Our preliminary results suggest that LPL34 contains lipase activity and may be involved in colon cancer development. We have proposed three specific aims to study this novel lysophospholipase. The outcome of these studies will provide important information about (1) the value of LPL34 as diagnostic/prognostic marker, (2) the molecular mechanism(s) of action of this novel lysophospholipase in normal cell growth and (3) its contribution in colon cancer development.