Acinus: A Novel Corepressor of RAR-Regulated Gene Expression

描述(申请人提供)：维甲酸(RA)是维生素A最有效的天然形式，在调节正常细胞和转化细胞的生长和分化方面发挥着重要作用。RA通过维甲酸受体(RARs)和维甲酸X受体(RXRs)转录调控基因表达。三种不同但高度同源的RAR亚型被描述为RARpha、RARbeta和RARGamma。RARs含有一个高度保守的DNA结合域(C域)、一个高度保守的配体结合域(E域)以及另外三个或四个保守程度较低的结构域(A、B、D和F)。关于RARs A/B结构域的功能的信息有限，但已知的是包含与位于E结构域的配体依赖的反式激活活性(AF-2)协同的配体非依赖性反式激活活性(AF-1)。本申请中提供的初步数据表明，腺泡蛋白是一种新的蛋白质，它特异性地与RARs的B结构域结合，并以非配体依赖的方式抑制转录。最近的报道表明，腺泡蛋白也可能是一个剪接因子。我们假设Acinus作为一种新的辅阻遏子蛋白，在RAR调节的转录和RAR调节的前-mRNAs的剪接的共转录调控中发挥重要作用。具体地说，我们将解决以下4个目标：(1)完成腺泡蛋白作为RAR结合蛋白的特征，以抑制RAR依赖的转录；(2)检测腺泡蛋白在介导RAR调节的基因表达和依赖RA的P19细胞分化中的作用；(3)检测腺泡蛋白特定丝氨酸残基的磷酸化在调节其细胞定位和抑制基因表达中的作用；以及(4)开始阐明腺泡杆菌改变RAR调节基因表达的机制。

DESCRIPTION (provided by applicant): Retinoic acid (RA), the most potent natural form of vitamin A, plays an important role in mediating the growth and differentiation of both normal and transformed cells. RA functions by transcriptionally regulating gene expression via retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Three distinct but highly homologous RAR subtypes have been described termed RARalpha, RARbeta and RARgamma. RARs contain a highly conserved DNA binding domain (domain C), a well conserved ligand binding domain (domain E), and three or four additional domains that are not as well conserved (domains A, B, D and F). There is a limited amount of information concerning the function of the A/B domains of RARs however it is known to contain ligand-independent transactivation activity (AF-1) that synergizes with the ligand- dependent transactivation activity (AF-2) located in the E domain. Preliminary data presented in this application demonstrate the identification of Acinus as a new protein that binds specifically to the B-domain of RARs and represses transcription in a ligand-independent fashion. Recently reports suggest that Acinus may also function as a splicing factor. We hypothesize that Acinus functions as a novel corepressor protein that plans an important role in the cotranscriptional regulation of both RAR-regulated transcription and the splicing of RAR-regulated pre-mRNAS. Specifically we will address the following 4 aims: (1) Complete the characterization of Acinus as a RAR binding protein that represses RAR-dependent transcription; (2) Examine the role of Acinus in mediating both RAR-regulated gene expression and RA-dependent differentiation of P19 cells; (3) Examine the role of phosphorylation of specific serine residues of Acinus in mediating its cellular localization and repression of gene expression; and (4) Begin to elucidate the mechanism by which Acinus alters RAR-regulated gene expression.