Acinus: A Novel Corepressor of RAR-Regulated Gene Expression

描述（由申请人提供）：维甲酸（RA）是维生素A的最有效的天然形式，在介导正常和转化细胞的生长和分化中起重要作用。RA通过视黄酸受体（RAR）和类维生素A X受体（RXR）转录调节基因表达发挥功能。已经描述了三种不同但高度同源的RAR亚型，称为RAR α、RAR β和RAR γ。RAR含有高度保守的DNA结合结构域（结构域C）、充分保守的配体结合结构域（结构域E）和三个或四个不那么保守的另外的结构域（结构域A、B、D和F）。关于RAR的A/B结构域功能的信息有限，但已知其含有配体非依赖性反式激活活性（AF-1），该活性与位于E结构域的配体依赖性反式激活活性（AF-2）协同作用。本申请中提供的初步数据证明了Acinus作为一种新蛋白的鉴定，该蛋白特异性结合RAR的B结构域并以配体非依赖性方式抑制转录。最近的研究表明腺泡也可能作为剪接因子发挥作用。我们假设腺泡作为一种新的辅阻遏蛋白发挥作用，该蛋白在RAR调节的转录和RAR调节的前mRNAS的剪接的共转录调节中起重要作用。具体而言，我们将致力于以下4个目标：（1）完成Acinus作为RAR结合蛋白的表征，其抑制RAR依赖性转录;（2）检测Acinus在介导RAR调节的基因表达和RA依赖性P19细胞分化中的作用;（3）研究腺泡特异性丝氨酸残基的磷酸化在介导其细胞定位和抑制基因表达中的作用;（4）开始阐明腺泡改变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.