Abstract 38: Saturated free fatty acids activate a c-Src-JNK1 axis within lipid rafts: Implications for the development of insulin resistance, obesity, and obesity-associated cancer

Abstract Obesity is a risk factor for the development of insulin resistance/type 2 diabetes and several types of cancer, including cancers of the colon, breast, liver, endometrium and esophagus. Obese individuals have increased levels of free fatty acids (FFAs) in their serum, and so we are investigating signaling pathways that are activated by FFAs in vitro to gain insight into pathways that may trigger insulin resistance and the activation of oncogenes in obese individuals in vivo. Obesity is associated with chronic activation of c-Jun NH2-terminal kinase (JNK)1 in liver, fat and muscle tissue, and studies using JNK1-deficient mice demonstrate that JNK activation is important for adiposity, peripheral insulin resistance and the production of the proinflammatory cytokines, but the mechanism of JNK1 activation in obesity is unclear. Our data demonstrate that JNK1 is activated by FFAs in vitro in a c-Src-dependent manner, and that activation of c-Src occurs within lipid rafts. Src-deficient murine embryonic fibroblasts (MEFs) and SYF MEFs, which are deficient in c-Src family kinases c-Src, c-Yes and c-Fyn, do not activate JNK1 after exposure to FFAs in vitro, while NIH 3T3 MEFs and SYF MEFs reconstituted with c-Src activate JNK1 normally. In contrast, SYF MEFs reconstituted with c-Yes and c-Fyn do not activate JNK1. Knockdown of c-Src with shRNA in HEK 293T cells also inhibits FFA-induced activation of JNK1, and inhibition of c-Src with pharmacologic inhibitors has the same effect in J774 mouse macrophages. Pharmacologic inhibition of c-Src also prevents the FFA-induced upregulation of tumor necrosis factor (TNF)-α mRNA in macrophages. Importantly, c-Src is activated within lipid rafts after FFA treatment, as seen by both detergent-dependent and detergent-independent methods of raft isolation. Interestingly, omega-3 polyunsaturated fatty acids (PUFAs), which can protect against the onset of obesity, will also block JNK activation following treatment with saturated FFAs, and we suspect that this effect may be due to the ability of PUFAs to exclude c-Src from lipid rafts. Finally, preliminary data suggests that c-Src may be aberrantly activated in liver tissue from obese mice that were fed a high-fat diet. Experiments are currently underway to verify the role of c-src in the activation of JNK1 in vivo by acutely infusing mice with a free fatty acid emulsion in the presence of a pharmacologic inhibitor of c-src. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 38.