Mechanisms and biological consequences of the nuclear receptor CAR activation

CAR和PXR是核受体超家族中NR1I亚家族的成员。我的实验室是第一个将CAR定性为药物激活的核受体的实验室，领导了世界范围的研究，以确定CAR和PXR的特征并确定它们的生物学作用。CAR和PXR不仅调节肝脏的药物代谢和处置，而且还调节能量代谢，如糖异生、脂肪异生和酮生。此外，它们还调节细胞生长和死亡信号，包括JNK1、p38MAPK、AKT和GADD45信号。因此，CAR和PXR现在被认为与各种肝脏毒性和疾病有关，如肝脏肿瘤。现在已经知道，这些受体在这些调节中既作为转录因子又作为信号转导。然而，它们的分子机制目前还不完全清楚。我们的工作发现，CAR在DBD内的苏氨酸38位被磷酸化，并被灭活。这种磷酸化是CAR功能分化的基本原理。例如，苯巴比妥通过结合EGF受体和/或胰岛素受体并抑制其下游ERK1/2信号来激活CAR，从而通过蛋白磷酸酶2A刺激苏氨酸38的脱磷。在PXR中，LBD内丝氨酸350的磷酸化调节其功能。DBD或LBD中的这些磷酸化基序在大多数核受体中都是保守的，这表明CAR和PXR的发现可以与许多其他核受体的研究相关联 雌激素受体(ER)在其DBD内保守CAR的丝氨酸216位的苏氨酸38。在小鼠的中性粒细胞和巨噬细胞等免疫细胞中，发现ER在丝氨酸216位被特异性磷酸化。Er Ki(Esr1S216A)小鼠携带非仿磷酸型丙氨酸突变，以研究这种磷酸化的生物学作用。Er Ki老鼠是有生育能力的，但会患上肥胖症。对大脑、小胶质细胞和Kupffer细胞(大脑或肝脏中的驻留巨噬细胞)的分析表明，这种磷酸化赋予ER抗炎和抗凋亡的能力。磷酸化的ER可以成为研究肥胖和炎症相关的神经退行性疾病等各种疾病及其机制的新靶点。Er Ki小鼠可以作为这些研究的很好的动物模型。维甲酸相关孤儿受体(ROR)在DBD内保守这种丝氨酸100的磷酸化。这种丝氨酸残基在苯巴比妥治疗后在小鼠肝脏中被磷酸化，调节CAR靶向基因。这些核受体似乎通过保守的磷酸化来进行通讯，调节基因和疾病的发展，以响应环境化学物质，并提供了一个很好的实验系统来研究这种通讯的分子机制。对药物治疗和/或生理/病理生理条件作出反应。有40个核受体与DBD保持这一主题，使我们能够将同一条通讯研究线延伸到远远超出这三个核受体的范围。

CAR and PXR are members of the NR1I subfamily within the nuclear receptor superfamily. My laboratory was the first to characterize CAR as a drug-activated nuclear receptor, leading world-wide investigations to characterize CAR and PXR and establish their biological roles. Both CAR and PXR regulate not only hepatic drug metabolism and disposition but also energy metabolism such as gluconeogenesis and lipogenesis and ketogenesis. In addition, they regulate cell growth and death signals as well, which includes JNK1, p38MAPK, AKT and GADD45 signals. Consequently, CAR and PXR have now been implicated in various hepatic toxicities and diseases such as liver tumors. It is now known that these receptors act as transcription factors as well as signal transducers in these regulations. However, their molecular mechanisms are not fully understood now. Our work found that CAR is phosphorylated at threonine 38 within the DBD and is inactivated. This phosphorylation is the underlying principle through which CAR functions diverge. For example, phenobarbital stimulates dephosphorization of threonine 38 by protein phosphatase 2A, by binding EGF receptor and/or insulin receptor and repressing their down-stream ERK1/2 signal for CAR activation. In PXR, phosphorylation of serine 350 within the LBD regulates its functions. These phosphorylation motifs within the DBD or LBD are conserved in the majority of nuclear receptors, suggesting that findings with CAR and PXR can be implicated in the investigations of numerous other nuclear receptors Estrogen receptor (ER) conserves threonine 38 of CAR at serine 216 within its DBD. With a phospho-Ser216peptide antibody, it was found that ER is specifically phosphorylated at serine 216 in immune cells such as neutrophils and macrophages in mice. ER KI (Esr1S216A) mice bearing a non-phosphomimetic alanine mutation were generated to investigate the biological roles of this phosphorylation. ER KI mice are fertile but develop obesity. Analysis of brains and microglia and Kupffer cells (resident macrophages in the brain or liver) showed that this phosphorylation confers anti-inflammatory and anti-apoptotic capabilities to ER Phosphorylated ER can be a novel target to investigate various diseases such as obesity and inflammation-related neurodegenerative diseases and their mechanisms. ER KI mice can be an excellent animal model for these investigations. Retinoid related orphan receptor (ROR) conserves this phosphorylation at serine 100 within the DBD. This serine residue becomes phosphorylated in mouse livers in response to phenobarbital treatment, regulating CAR-targeted genes. These nuclear receptors appears to communicate through the conserved phosphorylation, regulating genes and disease developments in response to environmental chemicals and providing an excellent experimental system to investigate the molecular mechanism of this communication. in response to drug treatments and/or physiological/pathophysiological conditions. There are 40 nuclear receptors which conserve this motif with the DBD, enabling us to extend the same line of communication study far beyond these three nuclear receptors.