Fatty acid modulation of epidermal growth factor-induced mouse mammary epithelial cell proliferation in vitro

Mammary epithelial cells were isolated from midpregnant BALB/c mice, grown in primary culture within collagen gels, and maintained with serum-free medium containing 10 ng/ml epidermal growth factor (EGF) as the mitogen. Supplementation of culture medium with the saturated fatty acid, Na-stearate (18:0), significantly attenuated, whereas treatment with the unsaturated fatty acid, Na-arachidonate (20:4), significantly enhanced mammary epithelial cell proliferation, as compared to untreated controls. Treatment with various doses of either 18:0 or 20:4 was also found to result in a direct dose-dependent enrichment of mammary epithelial cell membrane fatty acid composition and a concurrent decrease in the relative levels of other membrane fatty acids, as determined by gas chromatography. Administration of the prostaglandin synthesis inhibitor, indomethacin, significantly inhibited EGF-induced cell growth in all treatment groups, but did not alter the relative inhibitory (18:0) or stimulatory (20:4) effects of fatty acid treatment. EGF-induced PKC translocation into the membrane fraction of mammary epithelial cells was enhanced in 20:4 and attenuated in 18:0 treatment groups, as compared to controls. Western blot analysis of phospholipid-dependent protein kinase C isoenzymes showed that PKC alpha was the predominant isoenzyme present in mouse mammary epithelial cells grown in primary culture, and the molecular weight of this PKC isoenzyme was determined to be 85 kDa. These results suggest that supplementation of culture media with specific fatty acids is associated with significant alterations in mammary epithelial cell membrane fatty acid composition, PKC activation, and mitogenic responsiveness. Since EGF can induce both PKC activation and cell proliferation, and because PKC activation requires membrane-derived phospholipids and diacylglycerol, these data suggest that specific fatty acid modulation of mammary epithelial cell mitogenesis is mediated through alterations in PKC alpha activation.