Aboushadi N, Engfelt W H, Paton V G, Krisans S K
Department of Biology, San Diego State University, San Diego, California, USA.
J Histochem Cytochem. 1999 Sep;47(9):1127-32. doi: 10.1177/002215549904700904.
Our group and others have recently demonstrated that peroxisomes contain a number of enzymes involved in cholesterol biosynthesis that previously were considered to be cytosolic or located in the endoplasmic reticulum (ER). Peroxisomes have been shown to contain HMG-CoA reductase, mevalonate kinase, phosphomevalonate kinase, phosphomevalonate decarboxylase, isopentenyl diphosphate isomerase, and FPP synthase. Four of the five enzymes required for the conversion of mevalonate to FPP contain a conserved putative PTS1 or PTS2, supporting the concept of targeted transport into peroxisomes. To date, no information is available regarding the function of the peroxisomal HMG-CoA reductase in cholesterol/isoprenoid metabolism, and the structure of the peroxisomal HMG-CoA reductase has yet to be determined. We have identified a mammalian cell line that expresses only one HMG-CoA reductase protein, and which is localized exclusively to peroxisomes, to facilitate our studies on the function, regulation, and structure of the peroxisomal HMG-CoA reductase. This cell line was obtained by growing UT2 cells (which lack the ER HMG-CoA reductase) in the absence of mevalonate. The surviving cells exhibited a marked increase in a 90-kD HMG-CoA reductase that was localized exclusively to peroxisomes. The wild-type CHO cells contain two HMG-CoA reductase proteins, the well-characterized 97-kD protein localized in the ER, and a 90-kD protein localized in peroxisomes. We have also identified the mutations in the UT2 cells responsible for the lack of the 97-kD protein. In addition, peroxisomal-deficient Pex2 CHO cell mutants display reduced HMG-CoA reductase levels and have reduced rates of sterol and nonsterol biosynthesis. These data further support the proposal that peroxisomes play an essential role in isoprenoid biosynthesis.
我们小组和其他研究团队最近证实，过氧化物酶体含有多种参与胆固醇生物合成的酶，这些酶以前被认为存在于细胞质或内质网（ER）中。已证明过氧化物酶体含有3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶、甲羟戊酸激酶、磷酸甲羟戊酸激酶、磷酸甲羟戊酸脱羧酶、异戊烯基二磷酸异构酶和法尼基焦磷酸（FPP）合酶。甲羟戊酸转化为FPP所需的五种酶中有四种含有保守的假定过氧化物酶体靶向信号1（PTS1）或过氧化物酶体靶向信号2（PTS2），这支持了靶向转运至过氧化物酶体的概念。迄今为止，尚无关于过氧化物酶体HMG-CoA还原酶在胆固醇/类异戊二烯代谢中功能的信息，过氧化物酶体HMG-CoA还原酶的结构也尚未确定。我们已鉴定出一种仅表达一种HMG-CoA还原酶蛋白且该蛋白仅定位于过氧化物酶体的哺乳动物细胞系，以促进我们对过氧化物酶体HMG-CoA还原酶的功能、调节和结构的研究。该细胞系是通过在缺乏甲羟戊酸的条件下培养UT2细胞（缺乏内质网HMG-CoA还原酶）获得的。存活的细胞中一种90-kD的HMG-CoA还原酶显著增加，且该酶仅定位于过氧化物酶体。野生型中国仓鼠卵巢（CHO）细胞含有两种HMG-CoA还原酶蛋白，一种是在内质网中特征明确的97-kD蛋白，另一种是定位于过氧化物酶体的90-kD蛋白。我们还鉴定出了UT2细胞中导致缺乏97-kD蛋白的突变。此外，过氧化物酶体缺陷的Pex2 CHO细胞突变体显示HMG-CoA还原酶水平降低，固醇和非固醇生物合成速率降低。这些数据进一步支持了过氧化物酶体在类异戊二烯生物合成中起重要作用的观点。
