Servetnick D A, Brasaemle D L, Gruia-Gray J, Kimmel A R, Wolff J, Londos C
Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1995 Jul 14;270(28):16970-3. doi: 10.1074/jbc.270.28.16970.
Steroidogenic cells store cholesteryl esters, precursors for steroid hormone synthesis, in intracellular lipid droplets. Cholesteryl ester hydrolysis is activated by protein kinase A and catalyzed by cholesteryl esterase. The esterase is similar, if not identical, to hormone-sensitive lipase in adipocytes where an analogous lipolytic mechanism occurs. Perilipins, proteins located exclusively at lipid droplet surfaces in adipocytes, are polyphosphorylated by protein kinase A in response to lipolytic stimuli, suggesting a role for these proteins in mediating lipid metabolism. The present study reveals that perilipins are associated with cholesteryl ester droplets in two steroidogenic cell lines: Y-1 adrenal cortical cells and MA-10 Leydig cells. The relative abundance of perilipin mRNAs and protein is much less in steroidogenic cells than in adipocytes. Like adipocytes, steroidogenic cells express perilipin A; additionally, the latter cells contain relatively abundant amounts of perilipin C, a protein that is not detectable in adipocytes by Western analysis. The data suggest a strong link between perilipins and lipid hydrolysis that is mediated by the hormone-sensitive lipase/cholesteryl esterase class of enzymes.
类固醇生成细胞将胆固醇酯（类固醇激素合成的前体）储存在细胞内脂滴中。胆固醇酯水解由蛋白激酶A激活，并由胆固醇酯酶催化。该酯酶与脂肪细胞中的激素敏感性脂肪酶相似（即便不完全相同），脂肪细胞中也存在类似的脂解机制。脂周蛋白是仅位于脂肪细胞脂滴表面的蛋白质，在脂解刺激下会被蛋白激酶A多磷酸化，这表明这些蛋白质在介导脂质代谢中发挥作用。本研究表明，脂周蛋白与两种类固醇生成细胞系中的胆固醇酯滴相关：Y-1肾上腺皮质细胞和MA-10睾丸间质细胞。脂周蛋白mRNA和蛋白质的相对丰度在类固醇生成细胞中比在脂肪细胞中低得多。与脂肪细胞一样，类固醇生成细胞表达脂周蛋白A；此外，后一种细胞含有相对大量的脂周蛋白C，通过蛋白质免疫印迹分析在脂肪细胞中无法检测到这种蛋白质。数据表明脂周蛋白与由激素敏感性脂肪酶/胆固醇酯酶类酶介导的脂质水解之间存在紧密联系。
