Alternative splicing determines the interaction of SMRT isoforms with nuclear receptor-DNA complexes
Alternative splicing determines the interaction of SMRT isoforms with nuclear receptor-DNA complexes
复制标题
DOI：
10.1042/bsr20080093
复制
发表时间：
2009-06-01
影响因子：
4
通讯作者：
Sharpe, Colin R.
中科院分区：
文献类型：
--
作者：
Faist, Flavie;Short, Stephen;Sharpe, Colin R.
小分子的信号传导，如维甲酸，是由异源二聚体介导的，异源二聚体包括II类核受体和RXR（类维甲酸X受体）亚基。受体结合DNA应答元件并作为配体依赖的转录因子，但在缺乏信号的情况下，受体结合共阻遏物SMRT [RAR（视黄酸受体）和TR（甲状腺激素受体）的沉默介质]和NCoR（核受体共阻遏物）并抑制基因表达。哺乳动物SMRT转录物的选择性剪接产生六种同工异构体，其中包含1、2或3个核受体协同抑制因子（corr）盒基序，负责与核受体的相互作用。我们发现人类细胞系表达所有六种SMRT亚型，然后确定小鼠SMRT亚型对RAR/RXR和另外三种II类核受体- dna复合物的结合亲和力。这种方法证明了在指导SMRT与核受体的相互作用时，每个SMRT蛋白中完整的CoRNR盒补体的重要性，而不是单个CoRNR盒的身份。每一类SMRT异构体表现出不同的特征，1-box异构体区分DNA应答元件，2-box异构体促进与TR复合物的高亲和力结合，3-box异构体与核受体的差异结合。因此，在体内观察到的SMRT异构体的差异部署可以显著扩大核受体信号传导的调节能力。
Signalling by small molecules, such as retinoic acid, is mediated by heterodimers comprising a class II nuclear receptor and an RXR (retinoid X receptor) subunit. The receptors bind to DNA response elements and act as ligand-dependent transcription factors, but, in the absence of signal, the receptors bind the co-repressors SMRT [silencing mediator for RAR (retinoic acid receptor) and TR (thyroid hormone receptor)] and NCoR (nuclear receptor co-repressor) and repress gene expression. Alternative splicing of the SMRT transcript in mammals generates six isoforms containing 1, 2 or 3 CoRNR (co-repressor for nuclear receptor) box motifs which are responsible for the interactions with nuclear receptors. We show that human cell lines express all six SMRT isoforms and then determine the binding affinity of mouse SMRT isoforms for RAR/RXR and three additional class II nuclear receptor-DNA complexes. This approach demonstrates the importance of the full complement of CoRNR boxes within each SMRT protein, rather than the identity of individual CoRNR boxes, in directing the interaction of SMRT with nuclear receptors. Each class of SMRT isoform displays a distinct feature, as the 1-box isoform discriminates between DNA response elements, the 2-box isoforms promote high-affinity binding to TR complexes and the 3-box isoforms show differential binding to nuclear receptors. Consequently, the differential deployment of SMRT isoforms observed in vivo could significantly expand the regulatory capacity of nuclear receptor signalling.