Slotte J P, Tenhunen J, Pörn I
Department of Biochemistry and Pharmacy, Abo Akademi University, Turku, Finland.
Biochim Biophys Acta. 1990 Jun 27;1025(2):152-6. doi: 10.1016/0005-2736(90)90092-3.
The hydrolysis of sphingomyelin from cellular plasma membranes imposes many consequences on cellular cholesterol homeostasis by causing a rapid and dramatic redistribution of plasma membrane cholesterol within the cells (Slotte, J.P. and Bierman, E.L. (1988) Biochem. J. 250, 653-658). The objective of this study was to examine the effects of an extracellular cholesterol acceptor on the directions of the sphingomyelinase-induced cholesterol flow in cultured fibroblasts. We have used HDL3 as a physiological acceptor for cholesterol, and measured the effects of sphingomyelin hydrolysis on efflux and endogenous esterification of cellular [3H]cholesterol. Treatment of cells with sphingomyelinase did induce a dramatically increased esterification of plasma-membrane-derived [3H]cholesterol. The presence of HDL3 in the medium (100 micrograms/ml) did not prevent or reduce the extent of the sphingomyelinase-induced cellular esterification of [3H]cholesterol. Degradation of cellular sphingomyelin (75% hydrolysis) also did not enhance the rate of [3H]cholesterol efflux from the plasma membranes to HDL3. In addition, we also observed that the degradation of sphingomyelin in the HDL3 particles (complete degradation) did not change the apparent rate of [3H]cholesterol transfer from HDL3 to the cells. These findings together indicate that hydrolysis of sphingomyelin did not markedly affect the rates of cholesterol surface transfer between HDL3 and cells. By whatever mechanism cholesterol is forced to be translocated from the plasma membranes subsequent to the degradation of sphingomyelin, it appears that the sterol flow is specifically directed towards the interior of the cells.
细胞膜鞘磷脂的水解会导致细胞膜胆固醇在细胞内迅速且显著地重新分布，从而对细胞胆固醇稳态产生诸多影响（斯洛特，J.P.和比尔曼，E.L.（1988年）《生物化学杂志》250卷，653 - 658页）。本研究的目的是检测细胞外胆固醇受体对培养的成纤维细胞中鞘磷脂酶诱导的胆固醇流动方向的影响。我们使用高密度脂蛋白3（HDL3）作为胆固醇的生理受体，并测量鞘磷脂水解对细胞[³H]胆固醇流出和内源性酯化的影响。用鞘磷脂酶处理细胞确实会显著增加源自细胞膜的[³H]胆固醇的酯化。培养基中存在HDL3（100微克/毫升）并不能阻止或降低鞘磷脂酶诱导的细胞[³H]胆固醇酯化程度。细胞鞘磷脂的降解（75%水解）也没有提高[³H]胆固醇从细胞膜向HDL3的流出速率。此外，我们还观察到HDL3颗粒中鞘磷脂的降解（完全降解）并没有改变[³H]胆固醇从HDL3向细胞转移的表观速率。这些发现共同表明，鞘磷脂的水解并没有显著影响HDL3与细胞之间胆固醇表面转移的速率。无论鞘磷脂降解后胆固醇被迫从细胞膜转运的机制是什么，似乎固醇流动都特别指向细胞内部。
