Mouradian M, Kikawa K D, Johnson E D, Beck K L, Pardini R S
Department of Biochemistry and Molecular Biology, University of Nevada, Reno, 1664 N. Virginia St, MS0330, Reno, NV 89557.
Prostaglandins Leukot Essent Fatty Acids. 2014 Apr;90(4):105-115. doi: 10.1016/j.plefa.2013.12.001. Epub 2013 Dec 11.
The distribution of omega-6 and omega-3 polyunsaturated fatty acid (PUFA) intake in Western diets is disproportionate, containing an overabundance of the omega-6 PUFA, linoleic acid (LA; C18:2). Increased enrichment with LA has been shown to contribute to the enhancement of tumorigenesis in several cancer models. Previous work has indicated that phosphatidylinositol 3-kinase (PI3K) may play a key role in LA-induced tumorigenesis. However, the modes by which LA affects carcinogenesis have not been fully elucidated. In this study, a mechanism for LA-induced upregulation of cancer cell growth is defined. LA treatment enhanced cellular proliferation in BT-474 human breast ductal carcinoma and A549 human lung adenocarcinoma cell lines. Enrichment of LA increased cyclooxygenase (COX) activity and led to increases in prostaglandin E2 (PGE2), followed by increases in matrix metalloproteinase (MMP) and transforming growth factor alpha (TGF-α) levels, which are all key elements involved in the enhancement of cancer cell growth. Further investigation revealed that LA supplementation in both BT-474 breast and A549 lung cancer cell lines greatly increased the association between the scaffolding protein GRB2-associated-binding protein 1 (Gab1) and epidermal growth factor receptor (EGFR), although Gab1 protein levels were significantly decreased. These LA-induced changes were associated with increases in activated Akt (pAkt), a downstream signaling component in the PI3K pathway. Treatment with inhibitors of EGFR, PI3K and Gab1-specific siRNAs reversed the upregulation of pAkt, as well as the observed increases in cell proliferation by LA in both cell lines. A549 xenograft assessment in athymic nude mice fed high levels of LA exhibited similar increases in EGFR-Gab1 association and increased levels of pAkt, while mice fed with high levels of the omega-3 PUFA, docosahexaenoic acid (DHA; C22:6), demonstrated an opposite response. The involvement of Gab1 in LA-induced tumorigenesis was further defined utilizing murine cell lines that express high levels of Gab1. Significant increases in cell proliferation were observed with the addition of increasing concentrations of LA. However, no changes in cell proliferation were detected in the murine paired cell lines expressing little or no Gab1 protein, establishing Gab1 as major target in LA-induced enhancement of tumorigenesis.
西方饮食中ω-6和ω-3多不饱和脂肪酸（PUFA）的摄入量分布不均衡，富含过量的ω-6多不饱和脂肪酸亚油酸（LA；C18:2）。在几种癌症模型中，LA富集增加已被证明有助于促进肿瘤发生。先前的研究表明，磷脂酰肌醇3激酶（PI3K）可能在LA诱导的肿瘤发生中起关键作用。然而，LA影响致癌作用的方式尚未完全阐明。在本研究中，确定了LA诱导癌细胞生长上调的机制。LA处理增强了BT-474人乳腺导管癌细胞系和A549人肺腺癌细胞系的细胞增殖。LA富集增加了环氧化酶（COX）活性，导致前列腺素E2（PGE2）增加，随后基质金属蛋白酶（MMP）和转化生长因子α（TGF-α）水平增加，这些都是参与增强癌细胞生长的关键因素。进一步研究发现，在BT-474乳腺癌和A549肺癌细胞系中补充LA，尽管Gab1蛋白水平显著降低，但支架蛋白GRB2相关结合蛋白1（Gab1）与表皮生长因子受体（EGFR）之间的结合大大增加。这些LA诱导的变化与PI3K途径下游信号成分活化的Akt（pAkt）增加有关。用EGFR、PI3K抑制剂和Gab1特异性siRNA处理可逆转pAkt的上调，以及LA在两种细胞系中观察到的细胞增殖增加。在喂食高水平LA的无胸腺裸鼠中进行的A549异种移植评估显示，EGFR-Gab1结合类似增加，pAkt水平升高，而喂食高水平ω-3多不饱和脂肪酸二十二碳六烯酸（DHA；C22:6）的小鼠表现出相反的反应。利用表达高水平Gab1的小鼠细胞系进一步确定了Gab1在LA诱导的肿瘤发生中的作用。随着LA浓度增加，观察到细胞增殖显著增加。然而，在几乎不表达或不表达Gab1蛋白的小鼠配对细胞系中未检测到细胞增殖变化，这确立了Gab1是LA诱导肿瘤发生增强的主要靶点。
