OVEREXPRESSION OF HORMONE-SENSITIVE LIPASE IN CHINESE-HAMSTER OVARY CELLS LEADS TO ABNORMALITIES IN CHOLESTEROL HOMEOSTASIS

Hormone-sensitive lipase (HSL) is an intracellular enzyme that functio ns as both a neutral triglyceride and cholesteryl eater hydrolase. In order to explore the effects of HSL on cholesterol homeostasis, Chines e hamster ovary (CHO) cells were transfected with rat HSL and several different stable cell lines that overexpress HSL mRNA, HSL protein, an d HSL activity approximately 600-fold were isolated. Cells transfected with HSL contained less cholesteryl eaters and unesterified cholester ol than control cells. HSL transfectants expressed 20-60% fewer LDL re ceptors than control cells when grown in lipid-depleted media or in th e presence of mevinolin, as assessed by binding and degradation of LDL and immunoblotting of LDL receptors. In contrast, the rate of cholest erol synthesis and the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase were increased 3- to 14-fold in HSL transfectan ts grown in sterol replete media. The rate of cholesterol synthesis an d the activity of HMG-CoA reductase increased when cells were grown in lipid-depleted media, and remained markedly elevated compared to cont rol cells. These results show that the regulation of LDL receptor expr ession and cholesterol synthesis can be dissociated through the action s of HSL and suggest multiple control mechanisms for sterol-responsive genes.