Gaudin C, Ishikawa Y, Wight D C, Mahdavi V, Nadal-Ginard B, Wagner T E, Vatner D E, Homcy C J
Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York 10032, USA.
J Clin Invest. 1995 Apr;95(4):1676-83. doi: 10.1172/JCI117843.
Alterations in beta-adrenergic receptor-Gs-adenylyl cyclase coupling underlie the reduced catecholamine responsiveness that is a hallmark of human and animal models of heart failure. To study the effect of altered expression of Gs alpha, we overexpressed the short isoform of Gs alpha in the hearts of transgenic mice, using a rat alpha-myosin heavy chain promoter. Gs alpha mRNA levels were increased selectively in the hearts of transgenic mice, with a level 38 times the control. Despite this marked increase in mRNA, Western blotting identified only a 2.8-fold increase in the content of the Gs alpha short isoform, whereas Gs activity was increased by 88%. The discrepancy between Gs alpha mRNA and Gs alpha protein levels suggests that the membrane content of Gs alpha is posttranscriptionally regulated. The steady-state adenylyl cyclase catalytic activity was not altered under either basal or stimulated conditions (GTP + isoproterenol, GTP gamma S, NaF, or forskolin). However, progress curve studies did show a significant decrease in the lag period necessary for GppNHp to stimulate adenylyl cyclase activity. Furthermore, the relative number of beta-adrenergic receptors binding agonist with high affinity was significantly increased. Our data demonstrate that a relatively small increase in the amount of the coupling protein Gs alpha can modify the rate of catalyst activation and the formation of agonist high affinity receptors.
β-肾上腺素能受体-Gs-腺苷酸环化酶偶联的改变是心力衰竭的人类和动物模型的一个标志——儿茶酚胺反应性降低的基础。为了研究Gsα表达改变的影响，我们使用大鼠α-肌球蛋白重链启动子在转基因小鼠心脏中过表达Gsα的短异构体。转基因小鼠心脏中Gsα mRNA水平选择性增加，是对照水平的38倍。尽管mRNA有如此显著的增加，但蛋白质印迹法显示Gsα短异构体的含量仅增加了2.8倍，而Gs活性增加了88%。Gsα mRNA水平与Gsα蛋白水平之间的差异表明，Gsα的膜含量受到转录后调控。在基础或刺激条件下（GTP + 异丙肾上腺素、GTPγS、NaF或福斯可林），稳态腺苷酸环化酶催化活性均未改变。然而，进程曲线研究确实显示，GppNHp刺激腺苷酸环化酶活性所需的延迟期显著缩短。此外，与激动剂结合的高亲和力β-肾上腺素能受体的相对数量显著增加。我们的数据表明，偶联蛋白Gsα量的相对较小增加可以改变催化剂激活速率和激动剂高亲和力受体的形成。
