Tugwood J D, Holden P R, James N H, Prince R A, Roberts R A
Zeneca Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire, UK.
Arch Toxicol. 1998 Feb;72(3):169-77. doi: 10.1007/s002040050483.
The peroxisome proliferator class of non-genotoxic rodent hepatocarcinogens cause hepatocyte DNA synthesis, peroxisome proliferation and liver tumours when administered to rats and mice, but fail to induce S-phase or peroxisome proliferation in hepatocytes from other species including guinea-pigs, dogs, and primates including humans. There are compelling data that implicate a nuclear receptor, the peroxisome proliferator-activated receptor-alpha (PPARalpha) as an important mediator of the toxic and carcinogenic effects of peroxisome proliferators (PPs). We were interested to consider the guinea-pig as a possible model for human responses to these compounds. This manuscript describes the isolation of a full-length cDNA encoding PPARalpha from guinea-pig liver that is closely related to receptors identified previously in mouse, rat and human. RNA hybridisation experiments suggested that the livers of the PP-responsive rat and mouse contained relatively high levels of PPARalpha transcripts, whereas in human and guinea-pig liver PPARalpha mRNA was much less abundant. Functional analyses suggested that the guinea-pig PPARalpha was able to be activated by PPs. DNA binding studies using in vitro translated proteins showed that the guinea-pig receptor was able to bind specifically to DNA in the presence of the retinoid X receptor (RXR), and transient transfection assays showed that the guinea-pig PPARalpha was capable of being transcriptionally activated in a concentration-dependent fashion by the PPs Wy-14,643 and nafenopin. Also, in guinea-pig primary hepatocyte cultures, a dominant negative repressor of PPARalpha ablated the suppression of spontaneous apoptosis by PPs. Taken together, these data show that the 'non-responsive' guinea-pig expresses active PPARalpha in the liver at reduced levels, and may be a useful model for exploring the mechanisms underlying the human response to PPs.
非遗传毒性啮齿动物肝癌致癌物中的过氧化物酶体增殖剂类，在给予大鼠和小鼠时会导致肝细胞DNA合成、过氧化物酶体增殖和肝肿瘤，但在包括豚鼠、狗以及包括人类在内的灵长类动物的肝细胞中却不能诱导S期或过氧化物酶体增殖。有确凿的数据表明，一种核受体，即过氧化物酶体增殖物激活受体α（PPARα），是过氧化物酶体增殖剂（PPs）毒性和致癌作用的重要介质。我们有兴趣将豚鼠视为人类对这些化合物反应的一种可能模型。本手稿描述了从豚鼠肝脏中分离出的编码PPARα的全长cDNA，它与先前在小鼠、大鼠和人类中鉴定出的受体密切相关。RNA杂交实验表明，对PP有反应的大鼠和小鼠的肝脏中PPARα转录本水平相对较高，而在人类和豚鼠肝脏中，PPARα mRNA的含量要少得多。功能分析表明，豚鼠PPARα能够被PPs激活。使用体外翻译蛋白进行的DNA结合研究表明，豚鼠受体在视黄酸X受体（RXR）存在的情况下能够特异性结合DNA，瞬时转染实验表明，豚鼠PPARα能够被PPs Wy-14,643和萘酚平以浓度依赖的方式转录激活。此外，在豚鼠原代肝细胞培养物中，PPARα的显性负性抑制剂消除了PPs对自发凋亡的抑制作用。综上所述，这些数据表明，“无反应”的豚鼠肝脏中表达水平降低的活性PPARα，可能是探索人类对PPs反应潜在机制的有用模型。
