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 functions as both a neutral triglyceride and cholesteryl ester hydrolase. In order to explore the effects of HSL on cholesterol homeostasis, Chinese hamster ovary (CHO) cells were transfected with rat HSL and several different stable cell lines that overexpress HSL mRNA, HSL protein, and HSL activity approximately 600-fold were isolated. Cells transfected with HSL contained less cholesteryl esters and unesterified cholesterol than control cells. HSL transfectants expressed 20-60% fewer LDL receptors than control cells when grown in lipid-depleted media or in the presence of mevinolin, as assessed by binding and degradation of LDL and immunoblotting of LDL receptors. In contrast, the rate of cholesterol synthesis and the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase were increased 3- to 14-fold in HSL transfectants grown in sterol replete media. The rate of cholesterol synthesis and the activity of HMG-CoA reductase increased when cells were grown in lipid-depleted media, and remained markedly elevated compared to control cells. These results show that the regulation of LDL receptor expression and cholesterol synthesis can be dissociated through the actions of HSL and suggest multiple control mechanisms for sterol-responsive genes.
Kraemer
F B
FB
Department of Veterans Affairs Medical Center, Palo Alto, CA 94304, USA.
Fong
L
L
Patel
S
S
Natu
V
V
Komaromy
M C
MC
D000818:Animals; D016466:CHO Cells; D002784:Cholesterol / Q000096:biosynthesis / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D006224:Cricetinae; D015870:Gene Expression; D006706:Homeostasis; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D007700:Kinetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011973:Receptors, LDL / Q000378:metabolism; D002787:Sterol Esterase / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection
D002788:Cholesterol Esters; D012333:RNA, Messenger; D011973:Receptors, LDL; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D002787:Sterol Esterase