Lefebvre P, Gaub M P, Tahayato A, Rochette-Egly C, Formstecher P
CJF INSERM 92-03, Laboratoire de Biochimie Structurale Faculté de Médecine de Lille, France.
J Biol Chem. 1995 May 5;270(18):10806-16. doi: 10.1074/jbc.270.18.10806.
To determine which factors may regulate the DNA binding and transcriptional properties of retinoic acid receptors (RARs and RXRs), we investigated the sensitivity of reporter genes bearing various retinoic acid response elements (RAREs) to protein phosphatases (PPases) inhibition. PPases inhibition by okadaic acid led to an increase of the reporter genes activity in a RARE-dependent and ligand-independent manner and was dependent on the type of response element used. Overexpression of protein phosphatases 2A and 1 (PP2A and PP1) decreased the inducibility of the reporter genes tested. Nuclear extracts from okadaic acid-treated COS cells displayed an 2-5-fold increased level of receptor binding to RAREs in vitro, suggesting that PPases inhibition increased the DNA binding activity of retinoid receptors. Treatment of receptors extracted from COS cells by alkaline phosphatase and partially purified PP1 and PP2A decreased their DNA binding activity, but heterodimers bound to DNA were not sensitive to phosphatase treatment. Reconstitution experiments showed that phosphorylation of both receptors increased the DNA binding activity of RXR/RAR heterodimers. Taken together, these data show that the modulation of the phosphorylation state of RARs and RXRs represents an other level of regulation of the retinoid signaling pathway.
为了确定哪些因素可能调节视黄酸受体（RARs和RXRs）的DNA结合和转录特性，我们研究了携带各种视黄酸反应元件（RAREs）的报告基因对蛋白磷酸酶（PPases）抑制的敏感性。冈田酸对PPases的抑制导致报告基因活性以RARE依赖且不依赖配体的方式增加，并且取决于所使用的反应元件类型。蛋白磷酸酶2A和1（PP2A和PP1）的过表达降低了所测试报告基因的诱导性。来自经冈田酸处理的COS细胞的核提取物在体外显示受体与RAREs的结合水平增加了2至5倍，这表明PPases抑制增加了类视黄醇受体的DNA结合活性。用碱性磷酸酶以及部分纯化的PP1和PP2A处理从COS细胞中提取的受体降低了它们的DNA结合活性，但与DNA结合的异二聚体对磷酸酶处理不敏感。重组实验表明，两种受体的磷酸化均增加了RXR/RAR异二聚体的DNA结合活性。综上所述，这些数据表明，RARs和RXRs磷酸化状态的调节代表了类视黄醇信号通路的另一种调节水平。
