Approximately 30-50% of colorectal cancers contain KRas mutations, which confer resistance to standard therapy. A diet high in long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) is generally considered chemoprotective in regard to colon cancer. However, the molecular mechanisms by which n-3 PUFA suppresses tumorigenesis remain to be determined. Therefore, our overall goal is to define the role of n-3 PUFA in the modulation of oncogenic KRas-driven colon cancer. We hypothesized that n-3 PUFA would modify the biophysical properties of the plasma membrane though its incorporation into plasma membrane phospholipids. Utilizing quantitative fluorescence microscopy, we determined that n-3 PUFA reduce the rigidity of the plasma membrane of young adult mouse colonocytes (YAMC), CD3/CD28 activated CD4⁺ T cells, and colonic crypts derived from transgenic Fat-1 mice, which synthesize n-3 PUFA de novo. Interestingly, n-3 PUFA increased the rigidity of cytoskeletal free giant plasma membrane vesicles (GPMVs), derived from the aforementioned samples. Oncogenic Ras signaling is dependent on the formation of specific plasma membrane localized proteolipid complexes. Thus, it is noteworthy in YAMC cells and Drosophila midguts we documented for the first time that n-3 PUFA generates mix clusters of H- and K-Ras isoforms, which signal through ERK less efficiently. This resulted in a reduction of Ras driven colonic phenotypes in mice and Drosophila models. We then assessed the ability of n-3 PUFA to disrupt macropinocytosis, a cellular process in which extra cellular proteins are internalized through dynamic changes in plasma membrane lipids and cytoskeletal proteins. This process provides energy substrates that support the unique metabolic needs of Ras expressing cells. We determined that Ras expression mediates an increase in plasma membrane free cholesterol, which rigidifies the plasma membrane. Attenuating this rigidification by incorporating n-3 PUFA into the plasma membrane disrupted Ras driven macropinocytosis. Overall, we have demonstrated that n-3 PUFA ameliorate oncogenic Ras driven phenotypes through modification of plasma membrane biophysical properties leading to a disruption of Ras signaling. This reduces the ability of tumor cells to acquire energy substrate necessary to maintain its unique metabolic needs. These data contribute to the mechanistic understanding of how n-3 PUFA protect against colon cancer.
- Fish Oil
- N-3 PUFA