Abstract
Both increased de novo fatty acid synthesis and higher neutral lipid accumulation are a common phenotype observed in aggressive breast cancer cells, making lipid metabolism a promising target for breast cancer prevention. In the present studies, we demonstrate a novel effect of the active metabolite of vitamin D, 1α,25-dihydroxyvitamin D (1,25(OH)&sub2;D) on lipid metabolism in malignant breast epithelial cells. Treatment of MCF10CA1a breast epithelial cells with 1,25(OH)&sub2;D (10 nM) for 5 and 7 days decreased the level of triacylglycerol, the most abundant form of neutral lipids, by 20%(±3.9) and 50%(±5.9), respectively. In addition, 1,25(OH)&sub2;D treatment for 5 days decreased palmitate synthesis from glucose, the major fatty acid synthesized de novo (48%±5.5 relative to vehicle). We have further identified the anaplerotic enzyme pyruvate carboxylase (PC) as a target of 1,25(OH)&sub2;D-mediated regulation and hypothesized that 1,25(OH)&sub2;D regulates breast cancer cell lipid metabolism through inhibition of PC. PC mRNA expression was down-regulated with 1,25(OH)&sub2;D treatment at 2 (73%±6 relative to vehicle) and 5 (56%±8 relative to vehicle) days. Decrease in mRNA abundance corresponded with a decrease in PC protein expression at 5 days of treatment (54%±12 relative to vehicle). Constitutive overexpression of PC in MCF10CA1a cells using a pCMV6-PC plasmid inhibited the effect of 1,25(OH)&sub2;D on both TAG accumulation and de novo palmitate synthesis from glucose. Together, these studies demonstrate a novel mechanism through which 1,25(OH)&sub2;D regulates lipid metabolism in malignant breast epithelial cells.