DHA alters lipid raft organization and function in breast cancer cells

Background. Polyunsaturated fatty acids (PUFA), in particular docosahaexanoic acid (DHA), play beneficial roles in breast cancer prevention and therapy. Many studies have shown that DHA contributes to reduction of growth rate and induction of apoptosis. However, the mechanism by which n-3 PUFA inhibit breast cancer cells growth, is not yet well understood. It was suggested that these fatty acids might change the fluidity and structure of cell membrane, especially of lipid rafts. In fact the possible dismantling of lipid rafts is particularly important in cancer therapy. Aim. We propose that DHA alters raft structure which influences receptor function and signal transduction in breast cancer cells. Methods. Human breast cancer adenocarcinoma MDA-MB-231 cells, estrogen-insensible, were treated with DHA; we have isolated and analyzed lipid rafts from treated and untreated cells using protocols including or not detergents. Microdomains structure was also analyzed with atomic force microscopy (AFM). Results. We demonstrate, by HPLC-GC analysis, that DHA is incorporated and metabolized in breast cancer cells and in lipid rafts with different specificity for the phospholipids moiety. Of note is the observation that only the treatment with DHA, compared with other PUFA, reduces lipid raft cholesterol and sphingomyelin content, indicating a possible change in raft organization. Moreover our data suggest that DHA induces the exclusion EGF receptor from raft with a decrease of Ras raft localization and consequently a decrease of ERK activity. Conclusions. DHA incorporated into lipid rafts, induces the formation of “declustered rafts” with a reorganization of lipids and signal transduction proteins.