Fardoun Riham Zein, Asghar Mohammad, Lokhandwala Mustafa
Heart and Kidney Institute, College of Pharmacy, University of Houston, Houston, TX 77204, USA.
Free Radic Biol Med. 2007 Mar 15;42(6):756-64. doi: 10.1016/j.freeradbiomed.2006.11.033. Epub 2006 Dec 15.
Dopamine promotes sodium excretion, in part, via activation of D1 receptors in renal proximal tubules (PT) and subsequent inhibition of Na, K-ATPase. Recently, we have reported that oxidative stress causes D1 receptor-G-protein uncoupling via mechanisms involving protein kinase C (PKC) and G-protein-coupled receptor kinase 2 (GRK 2) in the primary cultures of renal PT of Sprague-Dawley (SD) rats. There are reports suggesting that redox-sensitive nuclear transcription factor, NF-kappaB, is activated in conditions associated with oxidative stress. This study was designed to identify the role of NF-kappaB in oxidative stress-induced defective renal D1 receptor-G-protein coupling and function. Treatment of the PT with hydrogen peroxide (H(2)O(2), 50 microM/20 min) induced the nuclear translocation of NF-kappaB, increased PKC activity, and triggered the translocation of GRK 2 to the proximal tubular membranes. This was accompanied by hyperphosphorylation of D1 receptors and defective D1 receptor-G-protein coupling. The functional consequence of these changes was decreased D1 receptor activation-mediated inhibition of Na, K-ATPase activity. Interestingly, pretreatment with pyrrolidine dithiocarbamate (PDTC, 25 microM/10 min), an NF-kappaB inhibitor, blocked the H(2)O(2)-induced nuclear translocation of NF-kappaB, increase in PKC activity, and GRK 2 translocation and hyperphosphorylation of D1 receptors in the proximal tubular membranes. Furthermore, PDTC restored D1 receptor G-protein coupling and D1 receptor agonist-mediated inhibition of the Na, K-ATPase activity. Therefore, we suggest that oxidative stress causes nuclear translocation of NF-kappaB in the renal proximal tubules, which contributes to defective D1 receptor-G-protein coupling and function via mechanisms involving PKC, membranous translocation of GRK 2, and subsequent phosphorylation of dopamine D1 receptors.
多巴胺部分通过激活肾近端小管（PT）中的D1受体并随后抑制钠钾ATP酶来促进钠排泄。最近，我们报道氧化应激通过涉及蛋白激酶C（PKC）和G蛋白偶联受体激酶2（GRK 2）的机制，导致Sprague-Dawley（SD）大鼠肾PT原代培养物中的D1受体-G蛋白解偶联。有报道表明，氧化还原敏感的核转录因子NF-κB在与氧化应激相关的条件下被激活。本研究旨在确定NF-κB在氧化应激诱导的肾D1受体-G蛋白偶联和功能缺陷中的作用。用过氧化氢（H₂O₂，50微摩尔/20分钟）处理PT可诱导NF-κB的核转位，增加PKC活性，并触发GRK 2向近端小管膜的转位。这伴随着D1受体的过度磷酸化和D1受体-G蛋白偶联缺陷。这些变化的功能后果是D1受体激活介导的钠钾ATP酶活性抑制降低。有趣的是，用NF-κB抑制剂吡咯烷二硫代氨基甲酸盐（PDTC，25微摩尔/10分钟）预处理可阻断H₂O₂诱导的NF-κB核转位、PKC活性增加、GRK 2转位以及近端小管膜中D1受体的过度磷酸化。此外，PDTC恢复了D1受体G蛋白偶联以及D1受体激动剂介导的钠钾ATP酶活性抑制。因此，我们认为氧化应激导致肾近端小管中NF-κB的核转位，这通过涉及PKC、GRK 2的膜转位以及随后多巴胺D1受体磷酸化的机制，导致D1受体-G蛋白偶联和功能缺陷。
