Han Z, Wax M B, Patil R V
Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Biol Chem. 1998 Mar 13;273(11):6001-4. doi: 10.1074/jbc.273.11.6001.
The molecular mechanisms for regulating water balance in many tissues are unknown. Like the kidney, the eye contains multiple water channel proteins (aquaporins) that transport water through membranes, including two (AQP1 and AQP4) in the ciliary body, the site of aqueous humor production. However, because humans with defective AQP1 are phenotypically normal and because the ocular application of phorbol esters reduce intraocular pressure, we postulated that the water channel activity of AQP4 may be regulated by these agents. We now report that protein kinase C activators, phorbol 12,13-dibutyrate, and phorbol 12-myristate 13-acetate strongly stimulate the phosphorylation of AQP4 and inhibit its activity in a dose-dependent manner. Phorbol 12,13-dibutyrate (10 microM) and phorbol 12-myristate 13-acetate (10 nM) reduced the rate of AQP4-expressing oocyte swelling by 87 and 92%, respectively. Further, phorbol 12,13-dibutyrate significantly increased the amount of phosphorylated AQP4. These results demonstrate that protein kinase C can regulate the activity of AQP4 through a mechanism involving protein phosphorylation. Moreover, they suggest important potential roles for AQP4 in several clinical disorders involving rapid water transport such as glaucoma, brain edema, and swelling of premature infant lungs.
许多组织中调节水平衡的分子机制尚不清楚。与肾脏一样，眼睛含有多种水通道蛋白（水孔蛋白），这些蛋白可通过膜运输水，包括睫状体（房水产生部位）中的两种（水通道蛋白1和水通道蛋白4）。然而，由于水通道蛋白1缺陷的人类在表型上是正常的，并且由于佛波酯的眼部应用可降低眼压，我们推测水通道蛋白4的水通道活性可能受这些药物调节。我们现在报告，蛋白激酶C激活剂佛波醇12,13 - 二丁酸酯和佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯强烈刺激水通道蛋白4的磷酸化，并以剂量依赖的方式抑制其活性。佛波醇12,13 - 二丁酸酯（10微摩尔）和佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（10纳摩尔）分别使表达水通道蛋白4的卵母细胞肿胀率降低了87%和92%。此外，佛波醇12,13 - 二丁酸酯显著增加了磷酸化水通道蛋白4的量。这些结果表明，蛋白激酶C可通过涉及蛋白质磷酸化的机制调节水通道蛋白4的活性。此外，它们提示水通道蛋白4在几种涉及快速水运输的临床疾病（如青光眼、脑水肿和早产儿肺肿胀）中具有重要的潜在作用。
