Kovacs Werner J, Tape Khanichi N, Shackelford Janis E, Duan Xueying, Kasumov Takhar, Kelleher Joanne K, Brunengraber Henri, Krisans Skaidrite K
Department of Biology, San Diego State University, San Diego, CA, USA.
Histochem Cell Biol. 2007 Mar;127(3):273-90. doi: 10.1007/s00418-006-0254-6. Epub 2006 Dec 19.
Previous studies have indicated that the early steps in the isoprenoid/cholesterol biosynthetic pathway occur in peroxisomes. However, the role of peroxisomes in cholesterol biosynthesis has recently been questioned in several reports concluding that three of the peroxisomal cholesterol biosynthetic enzymes, namely mevalonate kinase, phosphomevalonate kinase, and mevalonate diphosphate decarboxylase, do not localize to peroxisomes in human cells even though they contain consensus peroxisomal targeting signals. We re-investigated the subcellular localization of the cholesterol biosynthetic enzymes of the pre-squalene segment in human cells by using new stable isotopic techniques and data computations with isotopomer spectral analysis, in combination with immunofluorescence and cell permeabilization techniques. Our present findings clearly show and confirm previous studies that the pre-squalene segment of the cholesterol biosynthetic pathway is localized to peroxisomes. In addition, our data are consistent with the hypothesis that acetyl-CoA derived from peroxisomal beta-oxidation of very long-chain fatty acids and medium-chain dicarboxylic acids is preferentially channeled to cholesterol synthesis inside the peroxisomes without mixing with the cytosolic acetyl-CoA pool.
先前的研究表明，类异戊二烯/胆固醇生物合成途径的早期步骤发生在过氧化物酶体中。然而，过氧化物酶体在胆固醇生物合成中的作用最近在几份报告中受到质疑，这些报告得出结论，过氧化物酶体中的三种胆固醇生物合成酶，即甲羟戊酸激酶、磷酸甲羟戊酸激酶和甲羟戊酸二磷酸脱羧酶，在人类细胞中并不定位于过氧化物酶体，尽管它们含有一致的过氧化物酶体靶向信号。我们通过使用新的稳定同位素技术和同位素异构体光谱分析的数据计算，并结合免疫荧光和细胞通透技术，重新研究了人类细胞中前角鲨烯段胆固醇生物合成酶的亚细胞定位。我们目前的研究结果清楚地表明并证实了先前的研究，即胆固醇生物合成途径的前角鲨烯段定位于过氧化物酶体。此外，我们的数据与以下假设一致：源自极长链脂肪酸和中链二羧酸过氧化物酶体β氧化的乙酰辅酶A优先被引导至过氧化物酶体内的胆固醇合成，而不与胞质乙酰辅酶A池混合。
