Peffley D M, Gayen A K
Department of Pharmacology and Molecular Biology, Finch University of Health Sciences/The Chicago Medical School, Illinois 60064, USA.
Arch Biochem Biophys. 1997 Jan 15;337(2):251-60. doi: 10.1006/abbi.1996.9796.
Previously, we found that mevalonate-derived products together with an oxysterol regulated reductase synthesis at a posttranscriptional level. To determine which products were responsible for this regulation, either the squalene synthase inhibitor zaragozic acid A or the squalene cyclase inhibitor 4,4,10-beta-trimethyl-trans-decal-3beta-ol (TMD) was added to lovastatin-treated Syrian hamster cells in conjunction with mevalonate. Mevalonate alone decreased reductase synthesis 50% compared with lovastatin-treated cells. In contrast, when both zaragozic acid A and mevalonate were added to lovastatin-treated cells, there was no change in reductase synthesis. With either treatment, reductase mRNA levels did not change compared with lovastatin-treated cells. When both 25-hydroxycholesterol and mevalonate were added to lovastatin-treated cells, reductase synthesis and mRNA levels were decreased 95 and 50%, respectively. The 10-fold difference between changes in reductase synthesis and mRNA levels under these conditions reflects a specific effect of mevalonate-derived isoprenoids on reductase synthesis at the translational level. In contrast, coincubation of cells with mevalonate plus 25-hydroxycholesterol in the presence of zaragozic acid decreased reductase synthesis and mRNA levels 60 and 50%, respectively, compared with lovastatin-treated cells. Moreover, degradation of reductase was increased approximately 7-fold in cells treated with mevalonate alone but only 3-fold in cells treated with mevalonate and zaragozic acid A. These results indicate that isoprenoid products between mevalonate and squalene affect reductase at a posttranslational level by increasing degradation but do not regulate reductase synthesis at a posttranscriptional level. In contrast, when both TMD and mevalonate were added to lovastatin-treated cells, reductase synthesis was decreased approximately 50% with no corresponding decrease in reductase mRNA levels, similar to mevalonate only. Reductase degradation was increased approximately 7-fold under these conditions. Cellular incubation in TMD, mevalonate, and 25-hydroxycholesterol decreased reductase synthesis and mRNA levels 95 and 50%, respectively. From these results we concluded that mevalonate-derived nonsterols synthesized between squalene and lanosterol decrease reductase synthesis at a translational level-either alone or in combination with 25-hydroxycholesterol-and also increase reductase degradation.
此前，我们发现甲羟戊酸衍生产物与一种氧化甾醇在转录后水平调节还原酶的合成。为确定哪些产物负责这种调节，将鲨烯合酶抑制剂扎拉戈昔酸A或鲨烯环化酶抑制剂4,4,10-β-三甲基反式十氢萘-3β-醇（TMD）与甲羟戊酸一起添加到用洛伐他汀处理的叙利亚仓鼠细胞中。单独使用甲羟戊酸时，与用洛伐他汀处理的细胞相比，还原酶合成减少了50%。相比之下，当将扎拉戈昔酸A和甲羟戊酸都添加到用洛伐他汀处理的细胞中时，还原酶合成没有变化。无论哪种处理方式，与用洛伐他汀处理的细胞相比，还原酶mRNA水平均未改变。当将25-羟基胆固醇和甲羟戊酸都添加到用洛伐他汀处理的细胞中时，还原酶合成和mRNA水平分别降低了95%和50%。在这些条件下，还原酶合成变化与mRNA水平变化之间10倍的差异反映了甲羟戊酸衍生的类异戊二烯在翻译水平对还原酶合成的特异性作用。相比之下，在扎拉戈昔酸存在的情况下，将细胞与甲羟戊酸加25-羟基胆固醇共同孵育，与用洛伐他汀处理的细胞相比，还原酶合成和mRNA水平分别降低了60%和50%。此外，单独用甲羟戊酸处理的细胞中还原酶的降解增加了约7倍，但在用甲羟戊酸和扎拉戈昔酸A处理的细胞中仅增加了3倍。这些结果表明，甲羟戊酸和鲨烯之间的类异戊二烯产物通过增加降解在翻译后水平影响还原酶，但在转录后水平不调节还原酶的合成。相比之下，当将TMD和甲羟戊酸都添加到用洛伐他汀处理的细胞中时，还原酶合成减少了约50%，而还原酶mRNA水平没有相应降低，这与单独使用甲羟戊酸时相似。在这些条件下，还原酶降解增加了约7倍。用TMD、甲羟戊酸和25-羟基胆固醇进行细胞孵育分别使还原酶合成和mRNA水平降低了95%和50%。从这些结果我们得出结论，在鲨烯和羊毛甾醇之间合成的甲羟戊酸衍生的非甾醇单独或与25-羟基胆固醇联合在翻译水平降低还原酶合成，并且还增加还原酶的降解。
