Agonist and inverse agonist actions of β-blockers at the human β2-adrenoceptor provide evidence for agonist-directed signaling
Agonist and inverse agonist actions of β-blockers at the human β2-adrenoceptor provide evidence for agonist-directed signaling
复制标题
DOI：
10.1124/mol.64.6.1357
复制
发表时间：
2003-12-01
影响因子：
3.6
通讯作者：
Hill, SJ
中科院分区：
文献类型：
--
作者：
Baker, JG;Hall, IP;Hill, SJ
β-受体阻滞剂在心力衰竭中有有益的作用，尽管潜在的机制尚不清楚。β(2)--然而，在衰竭的心脏中，肾上腺素受体的比例更高。这项研究表明，几种临床使用的β-受体阻滞剂是人类β(2)-肾上腺素受体的激动剂。虽然在cAMP水平上这些激动剂作用很小，但在cAMP反应元件(CRE)介导的基因转录水平上它们是实质性的。“β-受体阻滞剂”在心力衰竭中的一些作用可能与这些化合物的β(2)-激动剂作用有关。Cre基因对β(2)激动剂、Forsklin和cAMP类似物的转录反应对p42/44丝裂原活化蛋白(MAP)激酶途径抑制剂敏感。Western blotting和酶联免疫吸附分析技术也直接显示了p42/44-MAP激酶的激活。N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline(H89；一种蛋白激酶A抑制剂)在蛋白激酶A被抑制的浓度下，通过β(2)-肾上腺素受体刺激cAMP积累和Cre基因转录，为另一种途径提供了证据。然而，心得安产生了矛盾的作用；它减少了基础cAMP的积累(通过β(2)介导的反向激动剂)，但刺激了β(2)介导的Cre基因转录。这不能用从Gs-腺苷环化酶-cAMP到Cre结合蛋白磷酸化的一系列途径来解释。心得安和普奈洛尔对百日咳毒素均不敏感，因此排除了胃肠道蛋白的影响。心得安Cre基因转录反应可被p42/44-MAP激酶抑制剂减弱，心得安也可直接刺激P42/44-MAP激酶通路。肌醇磷酸蓄积和蛋白激酶C或Rho激酶抑制剂对Cre基因转录的研究没有提供G(Q/11)或G(12/13)参与的证据。这些数据表明，普萘洛尔可以同时通过Gs偶联机制作为反向激动剂，同时通过另一种不依赖G蛋白的机制刺激p42/44-MAP激酶途径。
beta-Blockers have beneficial effects in heart failure, although the underlying mechanism is unknown. beta(2)-Adrenoceptors, however, are proportionally higher in the failing human heart. This study shows several clinically used beta-blockers are agonists at the human beta(2)-adrenoceptor. Although these agonist effects were small at the cAMP level, they were substantial at the level of cAMP response element (CRE)-mediated gene transcription. Some of the effects of "beta-blockers" seen in heart failure may be related to the beta(2)-agonist actions of these compounds. CRE-gene transcription responses to beta(2)-agonists, forskolin, and cAMP-analogs were sensitive to p42/44-mitogen-activated protein (MAP) kinase pathway inhibitors. p42/44-MAP kinase activation was also shown directly by western blotting and enzyme-linked immunosorbent assay techniques. N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89; a protein kinase A inhibitor) stimulated cAMP accumulation and CRE gene transcription via the beta(2)-adrenoceptor at concentrations at which protein kinase A was inhibited, providing evidence for an alternative pathway. Propranolol, however, produced paradoxical effects; it reduced basal cAMP accumulation (via beta(2)-mediated inverse agonism) but stimulated beta(2)-mediated CRE gene transcription. This cannot be explained by a sequential pathway from Gs-adenylyl cyclase-cAMP to CRE binding protein phosphorylation. Both responses to propranolol were insensitive to pertussis toxin, thus excluding Gi-protein involvement. Propranolol CRE gene transcription responses were attenuated by p42/44-MAP kinase inhibitors and propranolol was also found to directly stimulate the p42/44-MAP kinase pathway. Studies of inositol phosphate accumulation and of protein kinase C or Rho kinase inhibitors on CRE-gene transcription provided no evidence for G(q/11) or G(12/13) involvement. These data suggest that propranolol can simultaneously act as an inverse agonist through a Gs-coupled mechanism while stimulating the p42/44-MAP kinase pathway through an alternative G-protein-independent mechanism.