The Role of Docosahexaenoic Acid in Regulation of Epidermal Growth Factor Receptor Activation and Function

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase integral in regulating cell growth, survival, and migration. EGFR signaling, which is dependent on localization of the receptor within lipid rafts, is often hijacked during colon tumorigenesis. Previous work has found that docosahexaenoic acid (DHA) is protective against colon cancer. This fatty acid is proposed to function in part by perturbing lipid rafts and thereby altering cell signaling. The overall objective of this work was to determine whether DHA alters EGFR function and signaling.

 We assessed EGFR localization and ligand-induced phosphorylation in YAMC cells treated with fatty acids.  We found that DHA reduced the localization of EGFR to lipid rafts.  Concomitant with altering receptor localization, DHA was found to increase EGFR phosphorylation.  However, DHA paradoxically suppressed EGFR signal transduction.  We found that DHA uniquely altered EGFR activity, and other long chain polyunsaturated fatty acid did not exert the same effect.  We additionally observed similar effects on EGFR activation and signaling by feeding mice a diet enriched in fish oil (high in DHA), and this was attendant with reduced colon tumorigenesis.  

 We next probed the mechanism by which DHA enhances EGFR phosphorylation.  We found that DHA facilitates receptor dimerization to increase phosphorylation.  We additionally identified Ras activation as the site of perturbation of signal transduction.  DHA suppressed signal transduction by both changing the localization of EGFR within the plasma membrane and increasing receptor endocytosis and degradation.

 Lastly, we extended our observations into a wounding model.  Although DHA uniquely altered ligand-stimulated EGFR activity, both DHA and EPA altered EGFR transactivation and signaling upon injury.  This culminated in reduced wound healing in DHA and EPA treated cells.  In an animal model, we found that diets enriched in either DHA or EPA altered EGFR signaling in the colonocytes of wounded animals.

 Overall, we found that DHA modifies EGFR signaling, which can be beneficial or detrimental for health depending on the disease state of an individual.  These data help elucidate a mechanism by which DHA protects against colon cancer, as well as indicating a potential downside of n-3 PUFA therapy.