Molecular Studies on a Novel Receptor-type Transcription factor, AhR/Arnt.

以2,3,7,8四氯二苯并二氧芑为代表的环境污染物进入细胞后，除了诱导药物代谢酶外，还会产生各种不良的生物学效应，如致畸、促肿瘤、免疫缺陷和表皮发育不良等。这些作用被认为是由Ah受体（AhR）介导的。我们克隆了AhR的cDNA，并通过序列分析推断其主要结构为受体型转录因子，其n端具有新的bHLH和PAS结构域。PAS被认为是果蝇Per、Arnt （Ah受体核转运子）和果蝇Sim之间的保守序列。免疫化学分析显示，AhR抗体可以形成一个复合物结合XRE序列，XRE序列是一个诱导增强子序列，以响应ducers。AhR/Arnt复合物与Sp1协同增强CYP1A1基因的体外转录，模拟了基因在DNA转移实验中的转录。这两个转录因子在其同源DNA元件上相互作用以促进转录。从小鼠胚胎cDNA文库中分离到b/HLH/PAS家族新成员的cDNA克隆，采用RNA印迹杂交和全载原位杂交技术对其表达进行了研究。它们在发育中的胚胎的有限组织中特异性表达，表明它们在发育中的功能作用。其中一个克隆体是mSim，它是人类基因的小鼠复制品，被认为是唐氏综合症的致病基因。

When taken up in the cells, environmental pollutants usually represented by 2,3,7,8 tetrachlorodibenzodioxin exert various adverse biologicl effects such as teratogenesis, tumour promotion, immuno-decifiency, and epidermal dysplasia, in addition to induction of drug-metabolizing enzymes. These effects are considered to be mediated by Ah receptor (AhR). we cloned cDNA for AhR and deduced its primary structure from sequence analysis, which turned out to be a receptor-type transcription factor with novel bHLH and PAS domains at its N-terminus. The PAS is designated as a conserved sequence among Drosophila Per, Arnt (Ah receptor nuclear translocator) and Drosophila Sim.Immunochemical analysis revealed that AhR andarnt form a complex to bind the XRE sequence, an inducible enhancer sequence to in response to ducers. The AhR/Arnt complex enhanced in vitro transcription of CYP1A1 gene in cooperation with Sp1, mimicking the transcription of the gene in the DNA transfer experiments. The two transcription factors interacted with each other on their cognate DNA elements to enhance the transcription. cDNA clones of novel members of the b/HLH/PAS family were isolated from cDNA libraries of mouse embryos and their expressions were investigated by the RNA blot hybridization and whole mount in situ hybridization. They were expressed specifically in the limited tissues of the developing embryos, suggesting the functional roles in the development. One of the clones is mSim, a mouse counterpart of the human gene which is suggested to be a causative gene for Down Syndrome.