Wolf Irene M, Periyasamy Sumudra, Hinds Terry, Yong Weidong, Shou Weinian, Sanchez Edwin R
Department of Physiology & Pharmacology and the Center for Diabetes & Endocrine Research (CeDER), University of Toledo College of Medicine, 3035 Arlington Avenue, Toledo, OH 43614-5804, USA.
J Steroid Biochem Mol Biol. 2009 Jan;113(1-2):36-45. doi: 10.1016/j.jsbmb.2008.11.006. Epub 2008 Nov 27.
FKBP52 is a tetratricopeptide repeat (TPR) protein with peptidyl-prolyl isomerase activity and is found in steroid receptor complexes, including glucocorticoid receptor (GR). It is generally accepted that FKBP52 has a stimulatory effect on GR transcriptional activity. However, the mechanism by which FKBP52 controls GR is not yet clear, with reports showing effects on GR hormone-binding affinity and/or hormone-induced nuclear translocation. To address this issue, we have generated mice with targeted ablation of the FKBP52 gene. To date, no overt defects of GR-regulated physiology have been found in these animals, demonstrating that FKBP52 is not an essential regulator of global GR activity. To better assess the impact of FKBP52 on GR, mouse embryonic fibroblasts (MEFs) were generated from wild-type (WT) and FKBP52-deficient (KO) animals. Analysis of GR activity at reporter genes showed an approximate 70% reduction of activity in 52KO MEF cells, with no effect of FKBP52 loss on thyroid receptor. Interestingly, GR activity at endogenous genes was not globally affected in 52KO cells, with reduced activity at GILZ and FKBP51, but not at SGK and p21. Thus, FKBP52 appears to be a gene-specific modulator of GR. To investigate the mechanism of this action, analyses of GR heterocomplex composition, hormone-binding affinity, and ability to undergo hormone-induced nuclear translocation and DNA-binding were performed. Interestingly, no effect of FKBP52 loss was found for any of these GR properties, suggesting that the main function of FKBP52 is a heretofore-unknown ability to control GR activity at target genes. Lastly, loss of FKBP52 did not affect the ability of GR to undergo hormone-induced autologous down-regulation, showing that FKBP52 does not contribute to all branches of GR signaling. The implications of these results to the potential actions of FKBP52 on GR activity in vivo are discussed.
FKBP52是一种具有肽基脯氨酰异构酶活性的四肽重复序列（TPR）蛋白，存在于类固醇受体复合物中，包括糖皮质激素受体（GR）。普遍认为FKBP52对GR转录活性具有刺激作用。然而，FKBP52调控GR的机制尚不清楚，有报道显示其对GR激素结合亲和力和/或激素诱导的核转位有影响。为了解决这个问题，我们构建了FKBP52基因靶向敲除的小鼠。迄今为止，在这些动物中未发现GR调节的生理学有明显缺陷，这表明FKBP52不是整体GR活性的必需调节因子。为了更好地评估FKBP52对GR的影响，从小鼠野生型（WT）和FKBP52缺陷型（KO）动物中分离出小鼠胚胎成纤维细胞（MEF）。对报告基因处GR活性的分析表明，在52KO MEF细胞中活性降低了约70%，FKBP52缺失对甲状腺受体没有影响。有趣的是，52KO细胞中内源性基因处的GR活性并未受到整体影响，GILZ和FKBP51处的活性降低，但SGK和p21处没有。因此，FKBP52似乎是GR的基因特异性调节因子。为了研究这种作用的机制，我们对GR异源复合物组成、激素结合亲和力以及激素诱导的核转位和DNA结合能力进行了分析。有趣的是，FKBP52缺失对这些GR特性均无影响，这表明FKBP52的主要功能是一种迄今未知的控制靶基因处GR活性的能力。最后，FKBP52的缺失并不影响GR进行激素诱导的自身下调的能力，这表明FKBP52并非对GR信号传导的所有分支都有作用。我们讨论了这些结果对FKBP52在体内对GR活性潜在作用的影响。
