Liu Y, Kalintchenko N, Sassone-Corsi P, Aguilera G
Section on Endocrine Physiology, Developmental Endocrinology Branch, National Institute of Child Health and Human Development/NIH, CRC Room 1-3330, MSC 1303, Bethesda, MD 20892, USA.
J Neuroendocrinol. 2006 Jan;18(1):42-9. doi: 10.1111/j.1365-2826.2005.01383.x.
We have shown recently that the rapid decline in corticotrophin-releasing hormone (CRH) transcription following activation by stress is associated with induction and binding to the CRH promoter of the repressor isoforms of cAMP responsive element modulator (CREM), inducible cAMP early repressor (ICER). The ability of ICER to inhibit CRH transcription was examined in the hypothalamic cell line, 4B, which expresses CRH. Co-transfection of the inhibitory isoforms of CREM, ICER I and II and CREMbeta, and CRH promoter-luciferase constructs in 4B cells blunted basal and forskolin-stimulated CRH promoter activity, an effect which was abolished by mutation of the CRE of the CRH promoter. Western blot analyses and electromobility gel-shift and super-shift showed increases in endogenous ICER after 3 h of incubation with forskolin. Consistent with an inhibitory effect of CREM on CRH transcription, chromatin immunoprecipitation assays in cells transfected with ICER I revealed recruitment of CREM by the CRH promoter in conjunction with decreases in Pol II association. The study shows that generation of ICER following prolonged stimulation with forskolin, or transfection of an ICER expression vector in hypothalamic cell lines expressing CRH, is associated with CREM binding to the CRH promoter and transcriptional repression. The data support the hypothesis that induction of repressor isoforms of CREM is part of an intracellular feedback mechanism contributing to the termination of CRH transcription during stimulation.
我们最近发现，应激激活后促肾上腺皮质激素释放激素（CRH）转录的快速下降与环磷酸腺苷反应元件调节剂（CREM）的阻遏异构体、诱导型环磷酸腺苷早期阻遏物（ICER）与CRH启动子的诱导和结合有关。在表达CRH的下丘脑细胞系4B中检测了ICER抑制CRH转录的能力。在4B细胞中共转染CREM的抑制异构体ICER I和II以及CREMβ和CRH启动子-荧光素酶构建体，可减弱基础和福斯可林刺激的CRH启动子活性，CRH启动子的CRE突变可消除这种效应。蛋白质免疫印迹分析、电泳迁移率凝胶阻滞和超迁移显示，与福斯可林孵育3小时后内源性ICER增加。与CREM对CRH转录的抑制作用一致，用ICER I转染的细胞中的染色质免疫沉淀试验显示，CRH启动子募集了CREM，同时Pol II结合减少。该研究表明，用福斯可林长时间刺激后产生ICER，或在表达CRH的下丘脑细胞系中转染ICER表达载体，与CREM与CRH启动子的结合和转录抑制有关。这些数据支持了这样一种假说，即CREM阻遏异构体的诱导是细胞内反馈机制的一部分，有助于在刺激过程中终止CRH转录。
