Ishizaka N, Griendling K K, Lassègue B, Alexander R W
From the Department of Medicine, Division of Cardiology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Hypertension. 1998 Sep;32(3):459-66. doi: 10.1161/01.hyp.32.3.459.
Caveolae are membrane domains that have been implicated in signal transduction, and caveolins are major structural components of these domains. We found that all reported caveolin isoforms (caveolin-1, -2, and -3) were expressed in vascular smooth muscle cells (VSMCs); however, only caveolin-1 mRNA was regulated by angiotensin II (Ang II). Ang II (100 nmol/L) increased caveolin-1 mRNA, with a peak at 2 hours (193+/-6% of control, P<0.01, n=4). In contrast, Ang II significantly decreased caveolin-1 protein, with a nadir at 4 hours (64+/-5% of control, P<0.01, n=6). [35S]Methionine labeling showed that Ang II increased caveolin biosynthesis (226+/-33% of control labeling at 4 hours), suggesting that the transient decrease in caveolin protein levels is due to increased degradation. When cells were fractionated with sucrose, on agonist stimulation, AT1 receptors appeared in fraction 5 where caveolin was fractionated. This migration was blocked by low temperature and treatment with phenylarsine oxide, interventions that interfere with agonist-induced Ang II type 1 (AT1) receptor sequestration and tonic phase signaling. In addition, caveolin-1 coimmunoprecipitates with AT1 receptor only on agonist stimulation. These data support the concept that the caveola is a specialized signaling domain in VSMCs that can be dynamically accessed by the AT1 receptor. Because of the signaling and coupling proteins that are localized in caveolae and because of evidence that these proteins may interact directly with caveolin, caveola-AT1 receptor interaction likely represents an important focus for dynamic control of receptor signaling in VSMCs.
小窝是与信号转导有关的膜结构域，而小窝蛋白是这些结构域的主要结构成分。我们发现，所有已报道的小窝蛋白异构体（小窝蛋白-1、-2和-3）均在血管平滑肌细胞（VSMC）中表达；然而，只有小窝蛋白-1的mRNA受血管紧张素II（Ang II）调节。Ang II（100 nmol/L）可使小窝蛋白-1的mRNA增加，在2小时时达到峰值（为对照的193±6%，P<0.01，n=4）。相反，Ang II可使小窝蛋白-1的蛋白显著减少，在4小时时降至最低点（为对照的64±5%，P<0.01，n=6）。[35S]甲硫氨酸标记显示，Ang II可增加小窝蛋白的生物合成（4小时时为对照标记的226±33%），提示小窝蛋白水平的短暂下降是由于降解增加所致。当用蔗糖对细胞进行分级分离时，在激动剂刺激下，AT1受体出现在与小窝蛋白分级相同的第5级分中。这种迁移被低温和苯砷氧化物处理所阻断，这两种干预措施会干扰激动剂诱导的血管紧张素II 1型（AT1）受体的内吞和紧张相信号传导。此外，只有在激动剂刺激下，小窝蛋白-1才与AT1受体共免疫沉淀。这些数据支持这样一种概念，即小窝是VSMC中的一个特殊信号结构域，AT1受体可动态地与之结合。由于定位于小窝的信号和偶联蛋白，以及这些蛋白可能直接与小窝蛋白相互作用的证据，小窝-AT1受体相互作用可能是VSMC中受体信号动态控制的一个重要焦点。
