Redox Regulation of Signal Transduction Mechanism in the Heart

活性氧（ROS）由于其强烈的反应性而被认为是“邪恶的球员”。本文报道了一种ROS过氧化氢（H_2O_2）直接激活乳鼠心肌细胞G蛋白三聚体（G_i/G_0）。当H_2O_2激活G_i/G_0时，Gβγ从三聚体G_i/G_0中释放出来，释放的Gβγ激活ERK以保护细胞免受氧化损伤。我们已经鉴定了H_2O_2修饰的氨基酸，并发现H_2O_2介导的287和326位半胱氨酸残基的修饰是激活G_i所必需的。这些结果表明，ROS在心脏中可作为细胞内介质发挥作用，并提示由受体刺激产生的ROS可激活G_i和G_0。除H_2O_2处理细胞外，ROS的产生还与受体刺激有关。虽然血管紧张素II刺激产生ROS并诱导MAP激酶激活，但血管紧张素II刺激不能激活G_1和G_0。因此，我们得出结论，活性氧的量是一个重要的因素激活G蛋白。我们还发现，过氧化氧还蛋白II（PrxII）的表达消除了细胞内的ROS，PrxII消除了c-Jun NH_2-末端激酶（JNK）的激活，而不影响ERK和p38 MAPK的激活。结论：血管紧张素II激活特定的信号通路，导致JNK激活。这也表明ROS可以作为细胞内介质。

Reactive oxygen species (ROS) has been considered as an 'evil player' due to a strong reactivity. We have reported that trimeric G protein (G_i/G_0) is directly activated by one of ROS hydrogen peroxide (H_2O_2) in rat neonatal myocytes. Upon activation of G_i/G_0 by H_2O_2, Gβγis released from trimeric G_i/G_0 and the released Gβγ activates ERK to protect the cells against oxidative damage. We have now identified the amino acids that are modified by H_2O_2, and have found that the H_2O_2-mediated modification of cysteine residues located at 287 and 326 is necessary for activation of G_i. These results indicate that ROS can work as an intracellular mediator in the heart, and suggest that ROS generated by receptor stimulation can activate G_i and G_0. Other than the treatment of cells with H_2O_2, ROS was generated by receptor stimulation. Although angiotensin II stimulation generated ROS and induced MAP kinase activation, angiotensin II stimulation could not activate G_i and G_0. Therefore, we concluded that the amount of ROS is an important factor for activation of G protein. We have also found that the expression of peroxiredoxin II (PrxII) eliminates ROS from cells, and PrxII abolishes c-Jun NH_2-terminal kinase (JNK) activation without affecting ERK and p38 MAPK activation. It is concluded that angiotensin II activates specific signaling pathway leading to JNK activation. It also suggests that ROS can work as an intracellular mediator.