Role of poly ADP polymerase in transcriptional regulation by nuclear receptor

哺乳动物聚（adp -核糖）聚合酶（PARP）是一种核染色质相关蛋白，分子量为114 kDa，催化adp -核糖单位从NAD+转移到位于染色质内的核蛋白上。我们在这里报告了PARP作为核受体信号调节器的新特性的鉴定。PARP直接与类视黄醇X受体（RXR）结合，抑制由RXR异源二聚体和甲状腺激素受体（TR）介导的配体依赖性转录活性。相互作用表面位于RXRa的DNA结合区域。凝胶转移实验表明，PARP在反应元件上与TR/RXR异源二聚体结合。在瞬时转染实验中，过表达野生型PARP选择性地阻断了核受体功能，而酶缺陷突变型PARP未表现出明显的抑制作用，提示聚adp -核糖基酶活性在核受体基因调控中发挥了重要作用，并且融合到Gal4 DNA结合域的PARP抑制了含有Gal4结合位点的启动子的转录活性。因此，当募集到启动子时，PARP具有转录抑制活性。这些结果表明，聚adp核糖基化是基因转录的负辅助因子，调节核受体超家族成员。

Mammalian poly( ADP-ribose ) polymerase ( PARP ) is a nuclear chromatin-associated protein with molecular mass of 114 kDa that catalyzes the transfer of ADP-ribose units from NAD+ to nuclear proteins that are located within the chromatin. We report here the identification of a novel property of PARP as a modulator of nuclear receptor signalling. PARP directly bound to the retinoid X receptors ( RXR ) and repressed the ligand-dependent transcriptional activities mediated by the heterodimers of RXR and the thyroid hormone receptor ( TR ). The interacting surface is located in the DNA binding domain of RXRa. The gel shift assay demonstrated that PARP bound to the TR/RXR heterodimers on the response element. Overexpression of the wild-type PARP selectively blocked the nuclear receptor function in the transient transfection experiments, while the enzyme defective mutant PARP did not show significant inhibition, suggesting that the essential role of poly ADP-ribosyl enzymatic activity in the gene regulation by nuclear receptors, Furthermore the PARP fused to Gal4 DNA binding domain suppressed the transcriptional activity of promoter harboring Gal4 binding site. Thus the PARP has transcriptional represser activity when recruited to the promoter. These results indicates that poly ADP-ribosylation is a negative co factor in gene transcription, regulating the member of the nuclear receptor superfamily.