Kim R, Rine J, Kim S H
Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
Mol Cell Biol. 1990 Nov;10(11):5945-9. doi: 10.1128/mcb.10.11.5945-5949.1990.
Ras protein requires an intermediate of the cholesterol biosynthetic pathway for posttranslational modification and membrane anchorage. This step is necessary for biological activity. Maturation of Xenopus laevis oocytes induced by an oncogenic human Ras protein can be inhibited by lovastatin or compactin, inhibitors of the synthesis of mevalonate, an intermediate of cholesterol biosynthesis. This inhibition can be overcome by mevalonic acid or farnesyl diphosphate, a cholesterol biosynthetic intermediate downstream of mevalonate, but not by squalene, an intermediate after farnesyl pyrophosphate in the pathway. This study supports the idea that in Xenopus oocytes, the Ras protein is modified by a farnesyl moiety or its derivative. Furthermore, an octapeptide with the sequence similar to the C-terminus of the c-H-ras protein inhibits the biological activity of Ras proteins in vivo, suggesting that it competes for the enzyme or enzymes responsible for transferring the isoprenoid moiety (prenylation) in the oocytes. This inhibition of Ras prenylation by the peptide was also observed in vitro, using both Saccharomyces cerevisiae and Xenopus oocyte extracts. These observations show that Xenopus oocytes provide a convenient in vivo system for studies of inhibitors of the posttranslational modification of the Ras protein, especially for inhibitors such as peptides that do not penetrate cell membranes.
Ras蛋白需要胆固醇生物合成途径的一种中间产物进行翻译后修饰和膜锚定。这一步骤对于生物活性是必需的。致癌性人类Ras蛋白诱导的非洲爪蟾卵母细胞成熟可被洛伐他汀或美伐他汀抑制，这两种药物是胆固醇生物合成中间产物甲羟戊酸合成的抑制剂。这种抑制作用可被甲羟戊酸或法尼基二磷酸（甲羟戊酸下游的胆固醇生物合成中间产物）克服，但不能被鲨烯（该途径中法尼基焦磷酸之后的一种中间产物）克服。这项研究支持了在非洲爪蟾卵母细胞中Ras蛋白被法尼基部分或其衍生物修饰的观点。此外，一种序列与c-H-ras蛋白C末端相似的八肽在体内可抑制Ras蛋白的生物活性，这表明它在卵母细胞中竞争负责转移类异戊二烯部分（异戊二烯化）的一种或多种酶。使用酿酒酵母和非洲爪蟾卵母细胞提取物在体外也观察到了该肽对Ras异戊二烯化的这种抑制作用。这些观察结果表明，非洲爪蟾卵母细胞为研究Ras蛋白翻译后修饰的抑制剂提供了一个便利的体内系统，特别是对于像不穿透细胞膜的肽这样的抑制剂。
