Transcriptional regulation and cellular trafficking of aquaporin-2 water channel

我们研究了水通道蛋白-2 （AQP-2）在体内和体外系统中的调节机制。(1)体外实验：将小鼠AQP-2基因5′-侧翼区-9.5 kb的多个片段克隆到荧光素酶（Luc）报告质粒中，瞬时转染MDCK或mIMCD3细胞。高张力反应增强子至少位于两个片段，即张力反应增强子（TonE）（-570 ~ -560bp）和AQP-2基因5'侧区-6.1 ~ -4.3 kb之间的未知区域。后者与TonE具有不同的高渗反应结构和机制。它们独立于精氨酸抗利尿素（AVP）调节AQP-2的转录调节。-6.1 ~ -4.3 kb区域主要接收高渗性信号，但其调控进一步协同TonE激活AQP-2基因的转录。相反，TonE本身可能参与低张力调节AQP-2的转录。低渗本身不会改变Luc的基础活性，但会减弱camp诱导的Luc活性。这种作用是通过JNK介导的。这些发现表明，张力反应增强子位于AQP-2的5'侧区，并调节高张力和低张力诱导的AQP-2转录。(2)体内实验：观察衰老对糖皮质激素缺乏大鼠肾脏AQP-2表达的影响。糖皮质激素缺乏大鼠的水排泄功能受损，但老龄大鼠的水排泄功能受损程度较幼龄大鼠严重。衰老大鼠肾脏AQP-2表达降低。糖皮质激素缺乏大鼠血浆AVP未被充分抑制，老年糖皮质激素缺乏大鼠肾脏AQP-2 mRNA和蛋白表达明显上调。目前的研究结果表明，在糖皮质激素缺乏的老年大鼠中，AQP-2抗衰老的上调在依赖于AVP的非抑制性释放的水排泄持续损伤中起着至关重要的作用。少

We had examined the regulatory mechanism of aquaporin-2 (AQP-2) water channel in both in vitro and in vivo systems. (1) in vitro study : Various fragments of 5'-flanking region of murine AQP-2 gene up to -9.5 kb were cloned into a luciferase (Luc) reporter plasmid, and they were transiently transfected into MDCK or mIMCD3 cells. Hypertonicity-response enhancers were at least resided at two segments, namely tonicity-response enhancer (TonE)(-570〜-560bp) and unknown region between -6.1 and -4.3 kb of the 5'-flanking region of AQP-2 gene. The latter had the different structure and mechanism of response to hypertonicity from those of TonE. They regulated AQP-2 transcriptional regulation independently of arginine vasopressin (AVP). The region between -6.1 and -4.3 kb dominantly received hypertonicity signal, but its regulation further collaborated with TonE to activate the transcription of AQP-2 gene. On the contrary, TonE per se could be involved in hypotonicity-regulated AQP-2 transcripti … More on. Hypotonicity per se did not alter basal activity of Luc, but attenuated cAMP-induced Luc activity. This action was mediated through JNK. These findings indicate that tonicity-response enhancers are located at the 5'-flanking region of AQP-2, and regulate hyper- and hypotonicity-induced AQP-2 transcription. (2) in vivo study : We examined whether aging affects kidney expression of AQP-2 in glucocorticoid-deficient rats. Impaired water excretion was found in glucocorticoid-deficient rats, but its impairment was much serious in the aged rats compared with the young ones. Kidney AQP-2 expression was reduced in the aged rats. Plasma AVP was not sufficiently suppressed in the glucocorticoid-deficient t rats, and the expression of kidney AQP-2 mRNA and protein were rather upregulated in the aged rats with glucocorticoid deficiency. The present findings indicate that the upregulation of AQP-2 against aging plays a crucial role in persistent impairment in water excretion, dependent upon non-suppressible release of AVP, in aged rats with glucocorticoid deficiency. Less