An oxysterol-derived positive signal for 3-hydroxy-3-methylglutaryl-CoA reductase degradation in yeast
An oxysterol-derived positive signal for 3-hydroxy-3-methylglutaryl-CoA reductase degradation in yeast
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DOI：
10.1074/jbc.m007888200
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发表时间：
2001-03-23
影响因子：
4.8
通讯作者：
Hampton, RY
中科院分区：
文献类型：
--
作者：
Gardner, RG;Shan, H;Hampton, RY
甲羟戊酸途径的甾醇合成部分通过 3-羟基-3-甲基戊二酰辅酶 A 还原酶 (HMGR) 的反馈调节降解进行调节。在哺乳动物中，源自法尼基二磷酸 (FPP) 的非甾醇类异戊二烯信号和源自甾醇的信号似乎共同作用，积极调节 HMGR 降解速率。尽管甾醇衍生信号的性质和数量尚不清楚，但越来越多的证据表明氧甾醇可以发挥这种作用。在酵母中，FPP 产生的类似非甾醇类异戊二烯信号可积极调节 HMGR 降解，但迄今为止尚未揭示任何甾醇衍生信号的存在。我们现在通过使用氧化角鲨烯-羊毛甾醇环化酶的遗传和药理学操作证明，氧甾醇衍生的信号可正向调节酵母中的 HMGR 降解。氧甾醇衍生的信号通过特异性调节 HMGR 稳定性来发挥作用，而不是一般与内质网相关的降解。甲羟戊酸途径产物的直接生化标记证实氧甾醇是在酵母中内源产生的，并且它们的水平随着改变 HMGR 稳定性的遗传或药理学操作而适当变化。氧化角鲨烯-羊毛甾醇环化酶的基因操作确实导致气相色谱、气相色谱-质谱和MMR分析可检测到的24,25-氧化羊毛甾醇水平的增加，而在野生型细胞或角鲨烯环氧化酶下调的细胞中没有观察到可检测的水平。与哺乳动物细胞相反，酵母氧固醇衍生的信号对于酵母中的HMGR降解来说不是必需的。相反，该第二信号的功能是增强FPP衍生的信号促进HMGR降解的能力。因此，尽管确实存在差异，但酵母和哺乳动物细胞都采用相似的 HMGR 降解多输入调节策略。
Sterol synthesis by the mevalonate pathway is modulated, in part, through feedback-regulated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR). In mammals, both a non-sterol isoprenoid signal derived from farnesyl diphosphate (FPP) and a sterol-derived signal appear to act together to positively regulate the rate of HMGR degradation. Although the nature and number of sterol-derived signals are not clear, there is growing evidence that oxysterols can serve in this capacity. In yeast, a similar non-sterol isoprenoid signal generated from FPP acts to positively regulate HMGR degradation, but the existence of any sterol-derived signal has thus far not been revealed. We now demonstrate, through the use of genetic and pharmacological manipulation of oxidosqualene-lanosterol cyclase, that an oxysterol-derived signal positively regulated HMGR degradation in yeast. The oxysterol-derived signal acted by specifically modulating HMGR stability, not endoplasmic reticulum-associated degradation in general. Direct biochemical labeling of mevalonate pathway products confirmed that oxysterols were produced endogenously in yeast and that their levels varied appropriately in response to genetic or pharmacological manipulations that altered HMGR stability. Genetic manipulation of oxidosqualene-lanosterol cyclase did result in the buildup of detectable levels of 24,25-oxidolanosterol by gas chromatography, gas chromatography-mass spectroscopy, and MMR analyses, whereas no detectable amounts were observed in wild-type cells or cells with squalene epoxidase down-regulated. In contrast to mammalian cells, the yeast oxysterol-derived signal was not required for HMGR degradation in yeast, Rather, the function of this second signal was to enhance the ability of the FPP-derived signal to promote HMGR degradation. Thus, although differences do exist, both yeast and mammalian cells employ a similar strategy of multiinput regulation of HMGR degradation.