CYCLOOXYGENASE AND TUMORIGENESIS

流行病学研究表明，非甾体类抗炎药（NSAIDs）可以降低结肠癌的发病率。 由于阿司匹林和其他NSAID的药理学作用是抑制环氧合酶[考克斯，前列腺素（PG）生物合成中的限速酶]，因此可以推断NSAID的有益作用可能是通过抑制PG生物合成介导的。 然而，一些实验观察表明，NSAID的有益作用可能是通过COX依赖性和COX非依赖性途径介导的。 因此，具体目标是：1）确定通过用组成型表达的考克斯-1或诱导型考克斯-2 cDNA转染在结肠癌细胞系或正常肠上皮细胞中过表达考克斯是否导致肿瘤发生表型的变化，以及通过NSAID抑制考克斯是否消除体外（培养中的细胞）和体内（移植到无胸腺裸鼠的肿瘤生长）的变化。 这些研究的结果将建立或否定考克斯与肿瘤细胞生长的直接联系。 2)确定NSAID的环氧合酶非依赖性效应是否通过丝裂原活化蛋白激酶（MAPK）、NF κ B或过氧化物酶体增殖物激活受体（PPAR）信号通路介导。 最近的证据表明，NSAID调节MAPK、NF κ B和PPAR信号通路。 因此，这些研究的目的是确定COX非依赖性信号通路通过NSAID抑制肿瘤发生。 3)应用消减杂交和基因表达系列分析方法，筛选过表达考克斯-2的结肠癌细胞株和正常肠上皮细胞中差异表达的基因。鉴定由癌细胞中考克斯-2或NSAID治疗的过表达引起的上调或下调基因将提供关于增加的前列腺素产生如何导致致瘤表型变化的线索，或鉴定NSAID作用的细胞靶点（除了考克斯）的线索。 4)确定激活腺苷酸环化酶的前列腺素受体在结肠癌细胞中与正常细胞相比是否差异表达，并鉴定前列腺素E受体（Ep 2）的下游信号通路。了解前列腺素及其信号通路在癌细胞中的作用可以帮助探索新的治疗和/或预防策略，用于结肠癌和其他癌症，使用调节前列腺素生物合成的药理学药物和/或饮食手段。

Epidemiological studies have demonstrated that nonsteroidal antiinflammatory drugs (NSAIDs) can reduce the incidence of colon cancer. Since the well-documented pharmacological action of aspirin and other NSAIDs is inhibition of cyclooxygenase [COX, the rate limiting enzyme in prostaglandin (PG) biosynthesis], it can be inferred that the beneficial effect of NSAIDs may be mediated through the inhibition of PG biosynthesis. However, several lines of experimental observations imply that the beneficial effects of NSAIDs may be mediated through both COX-dependent and COX-independent pathways. Thus, Specific Aims are: 1) To determine whether the overexpression of COX in colon cancer cell lines or normal intestinal epithelial cells by transfecting with constitutively expressed COX-1 or inducible COX-2 cDNA, results in changes in tumorigenic phenotypes, and whether inhibiting COX by NSAIDs abrogates the changes in vitro (cells in culture) and in vivo (growth of transplanted tumors to athymic nude mice). Results from these studies will establish or negate a direct link of COX to tumor cell growth. 2) To determine whether cyclooxygenase-independent effects of NSAIDs are mediated through mitogen-activated protein kinase (MAPK), NFkappaB or peroxisome proliferator-activated receptor (PPAR) signaling pathways. Recent evidence suggests that NSAIDs modulate MAPK, NFkappaB and PPAR signaling pathways. Thus, these studies are aimed to identify COX-independent signaling pathways through which NSAIDs suppress tumorigenesis. 3) To identify differentially expresssed genes in the colon cancer line and normal intestinal epithelial cells overexpressing COX-2 by subtractive hybridization and Serial Analysis of Gene Expression methods. Identifying up-or-down-regulated genes caused by the overexpression of COX-2 or NSAID treatment in the cancer cells will provide a clue as to how increased prostaglandin production can lead to changes in tumorigenic phenotypes, or a clue to identifying the cellular targets (other than COX) of the NSAID actions. 4) To determine whether prostaglandin receptors that activate adenylate cyclase are differentially expressed in the colon cancer cells as compared with normal cells and to identify downstream signaling pathways of prostaglandin E receptor (Ep2). Understanding the roles of prostaglandins and their signaling pathways in cancer cells could help explore new treatments and/or preventive strategies for colon cancer and perhaps other cancers using pharmacological agents and/or dietary means that modulate prostaglandin biosynthesis.