Chen H, Born E, Mathur S N, Field F J
Department of Internal Medicine, University of Iowa, Iowa City.
J Lipid Res. 1993 Dec;34(12):2159-67.
There is a presumed association between cellular cholesterol and sphingomyelin metabolism. To study this relationship in the intestine, the activity of the rate controlling enzyme of sphingolipid synthesis, serine palmitoyltransferase (SPT), and the biosynthesis of long-chain bases were characterized in cultured human intestinal cells, CaCo-2. Cells were then incubated with substances known to alter cholesterol biosynthesis, and the effect of these mediators on SPT activity and long-chain base synthesis was determined and compared with their effects on HMG-CoA reductase activity and cholesterol synthesis. The polar sterol, 25-hydroxycholesterol, the squalene epoxide inhibitor, U18666A, and the inhibitor of HMG-CoA reductase, lovastatin, all significantly inhibited the synthesis of cholesterol without altering either SPT activity or long-chain base synthesis. Mevalonate, which increased cholesterol production 3-fold, also had no affect on SPT activity or sphingoid base synthesis. Serine, which significantly increased the synthesis of long-chain bases, did not alter cholesterol biosynthesis. Moreover, the suicide inhibitors of SPT, beta-chloroalanine and cycloserine, did not alter cholesterol synthesis while markedly decreasing long chain base synthesis. Cells were incubated with palmitic, oleic, linoleic, and eicosapentaenoic acids. Only palmitic acid, the preferred substrate for SPT, increased the production of long-chain bases. Both palmitic and oleic acids, however, increased the synthesis of cholesterol. Cells enriched in sphingomyelin had higher rates of synthesis of both cholesterol and long-chain bases compared to their controls. In contrast, cholesterol and long-chain base syntheses were significantly decreased in cells enriched in cholesterol. Control cells incubated with phospholipid liposomes alone had higher rates of synthesis of both lipids.(ABSTRACT TRUNCATED AT 250 WORDS)
细胞胆固醇与鞘磷脂代谢之间可能存在关联。为了研究肠道中的这种关系，在培养的人肠道细胞CaCo-2中对鞘脂合成的限速酶丝氨酸棕榈酰转移酶（SPT）的活性以及长链碱基的生物合成进行了表征。然后将细胞与已知会改变胆固醇生物合成的物质一起孵育，确定这些介质对SPT活性和长链碱基合成的影响，并将其与它们对HMG-CoA还原酶活性和胆固醇合成的影响进行比较。极性固醇25-羟基胆固醇、鲨烯环氧酶抑制剂U18666A和HMG-CoA还原酶抑制剂洛伐他汀均显著抑制胆固醇的合成，而不改变SPT活性或长链碱基合成。使胆固醇产量增加3倍的甲羟戊酸对SPT活性或鞘氨醇碱基合成也没有影响。显著增加长链碱基合成的丝氨酸并未改变胆固醇的生物合成。此外，SPT的自杀性抑制剂β-氯丙氨酸和环丝氨酸并未改变胆固醇合成，却显著降低了长链碱基合成。将细胞与棕榈酸、油酸、亚油酸和二十碳五烯酸一起孵育。只有棕榈酸（SPT的首选底物）增加了长链碱基的产生。然而，棕榈酸和油酸均增加了胆固醇的合成。与对照相比，富含鞘磷脂的细胞中胆固醇和长链碱基的合成速率更高。相反，富含胆固醇的细胞中胆固醇和长链碱基的合成显著降低。单独用磷脂脂质体孵育的对照细胞中两种脂质的合成速率更高。（摘要截短于250字）
