Bocos C, Göttlicher M, Gearing K, Banner C, Enmark E, Teboul M, Crickmore A, Gustafsson J A
Department of Medical Nutrition, Karolinska Institute, Huddinge University Hospital, Sweden.
J Steroid Biochem Mol Biol. 1995 Jun;53(1-6):467-73. doi: 10.1016/0960-0760(95)00093-f.
Peroxisome proliferators such as clofibric acid, nafenopin, and WY-14,643 have been shown to activate peroxisome proliferator-activated receptor (PPAR), a member of the steroid nuclear receptor superfamily. We have cloned the cDNA from rat that is homologous to that from mouse, which encodes a 97% similar protein. To search for physiologically occurring activators, we established a transcriptional transactivation assay by stably expressing in CHO cells a chimera of rat PPAR and the human glucocorticoid receptor that activates expression of the placental alkaline phosphatase reporter gene under the control of the mouse mammary tumor virus promoter. 150 microM concentrations of arachidonic or linoleic acid but not of dehydroepiandrosterone, cholesterol, or 25-hydroxy-cholesterol, activated the receptor chimera. In addition, saturated fatty acids induced the reporter gene. Shortening the chain length to n = 6 or introduction of an omega-terminal carboxylic group abolished the activation potential of the fatty acid. To test whether a common PPAR binding metabolite might be formed from free fatty acids we tested the effects of differentially beta-oxidizable fatty acids and inhibitors of fatty acid metabolism. The peroxisomal proliferation-inducing, non-beta-oxidizable, tetradecylthioacetic acid activated PPAR to the same extent as the strong peroxisomal proliferator WY-14,643, whereas the homologous beta-oxidizable tetradecylthiopropionic acid was only as potent as a non-substituted fatty acid. Cyclooxygenase inhibitors, radical scavengers or cytochrome P450 inhibitors did not affect activation of PPAR. In conclusion, beta-oxidation is apparently not required for the formation of the PPAR-activating molecule and this moiety might be a fatty acid, its ester with CoA, or a further derivative of the activated fatty acid prior to beta-oxidation of the acyl-CoA ester.
诸如氯贝酸、萘酚平以及WY-14,643等过氧化物酶体增殖剂已被证明可激活过氧化物酶体增殖物激活受体（PPAR），它是类固醇核受体超家族的一员。我们已从大鼠中克隆出与小鼠同源的cDNA，其编码的蛋白质相似度达97%。为寻找生理上存在的激活剂，我们通过在CHO细胞中稳定表达大鼠PPAR与人类糖皮质激素受体的嵌合体，建立了一种转录反式激活分析方法，该嵌合体在小鼠乳腺肿瘤病毒启动子的控制下激活胎盘碱性磷酸酶报告基因的表达。150微摩尔浓度的花生四烯酸或亚油酸可激活受体嵌合体，而脱氢表雄酮、胆固醇或25-羟基胆固醇则不能。此外，饱和脂肪酸可诱导报告基因。将链长缩短至n = 6或引入ω-末端羧基会消除脂肪酸的激活潜力。为测试游离脂肪酸是否可能形成共同的PPAR结合代谢物，我们测试了不同β-氧化脂肪酸和脂肪酸代谢抑制剂的作用。过氧化物酶体增殖诱导性、非β-氧化的十四烷基硫代乙酸激活PPAR的程度与强过氧化物酶体增殖剂WY-14,643相同，而同源的可β-氧化的十四烷基硫代丙酸的效力仅与未取代的脂肪酸相当。环氧化酶抑制剂、自由基清除剂或细胞色素P450抑制剂均不影响PPAR的激活。总之，PPAR激活分子的形成显然不需要β-氧化，该部分可能是脂肪酸、其与辅酶A的酯，或是酰基辅酶A酯β-氧化之前活化脂肪酸的进一步衍生物。
