Cloning and functional analysis of the mouse vasopressin/angiotensin II dual receptor

血管紧张素II/血管加压素双受体(AT/VPR)基因是从大鼠中克隆的，其蛋白产物具有独特的受体特性，即血管紧张素II(AII)和血管加压素(VP)都作为配体。然而，该基因的结构尚未确定，其受体的功能特性也有待阐明。在本研究中，我们克隆了小鼠AT/VPR的mRNA和基因(6.5kb)。虽然小鼠和大鼠的AT/AVPR基因在核苷酸序列上具有极高的相似性，但出乎意料的是，在小鼠中，大鼠基因的起始密码子从Met改变为Leu，导致N-末端的蛋白质产物延伸(179 A.A.)。比较小鼠AT/VPR基因的核苷酸序列，该基因至少由5个外显子和4个内含子组成。有趣的是，该基因与病原体识别受体Nacht/Nalp6部分同源。然后，我们检测了AT/VPR基因的组织分布，发现它在垂体、丘脑、大脑皮层、海马、小脑、肝脏、胆囊、肾上腺、结肠、睾丸和白色脂肪组织中表达。在心肌细胞中表达很弱，在骨骼肌、皮肤和脾中没有表达。最后，我们构建了该受体的表达载体，并在体外培养的大鼠血管平滑肌细胞中表达。我们认为，至少在我们的实验条件下，AII不会激活任何细胞内信号通路。另一方面，当AT/VPR过表达时，加压素适度增强依赖SRE的转录的反应，而显著减弱依赖于NF-kB的转录的反应。因此，我们认为AT/VPR可能不是作为经典的“激素受体”而是作为模式识别受体发挥作用，并且正在改变依赖于NF-kB的基因的转录。小鼠和大鼠AT/VPR的功能差异有待进一步研究。

Angiotensin II/vasopressin dual receptor (AT/VPR) gene was cloned from the rat, the protein product of which has unique receptor characteristics, i.e. both angiontensin II (AII) and vasopressin (VP) act as ligands. However, the structure of the gene has not characterized yet, and the functional characteristics of the receptor remains to be clarified. In this study, we cloned the mouse AT/VPR mRNA and gene (6.5 Kb). Although the mouse and the rat AT/AVPR genes showed extremely high similarity in their nucleotide sequences, unexpectedly, the initiation codon of the rat gene was changed from Met to Leu in the mouse, resulting in extended protein product at N-terminus (179 a.a.). The mouse AT/VPR gene consisted of at least 5 exons and 4 introns by comparing the nucleotide sequence of its cDNA. Interestingly, the gene partly shared that of NACHT/Nalp6,which belongs the pathogen-recognition receptor.We then examined the tissue distribution of the AT/VPR mRNA, and found it to be expressed in the pituitary, thalamus, cerebral cortex, hippocampus, cerebellum, liver, gall bladder, adrenal gland, colon, testis, and white adipose tissue.Expression in cardiomyocytes was weak, and no expression was observed in skeletal muscle, skin, and spleen.Finally, we constructed an expression vector of the receptor and expressed it in A10 rat vascular smooth muscle cells in vitro. We fund that, at least in our experimental condition, AII did not activate any intracellular signaling pathways. On the other hand, vasopressin modestly enhanced the response of SRE-dependent transcription, whereas markedly attenuated that of NF-kB-dependent transcription, when the AT/VPR was overexpressed.We thus conclude that AT/VPR may be working not as a classical "hormone receptor" but as a pattern recognition receptor, and is modifying the NF-kB-dependent gene transcription. The functional differences between the mouse and rat AT/VPR awaits further investigation.