Cellular G protein-coupled receptor kinase levels regulate sensitivity of the α2B-adrenergic receptor to undergo agonist-induced down-regulation
Cellular G protein-coupled receptor kinase levels regulate sensitivity of the α2B-adrenergic receptor to undergo agonist-induced down-regulation
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DOI：
10.1124/jpet.104.076042
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发表时间：
2005-02-01
影响因子：
3.5
通讯作者：
Eikenburg, DC
中科院分区：
文献类型：
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作者：
Desai, AN;Standifer, KM;Eikenburg, DC
最近有报道称，与单独激活α (2B)-AR相比，α (2B)-和β(2)-肾上腺素受体（AR）的慢性共激活可以在较低阈值肾上腺素（EPI）浓度下下调α (2B)-AR。这是G蛋白偶联受体激酶3 （GRK3）适度β (2)- ar依赖性上调的结果。在本研究中，研究人员发现，增加GRK2或GRK3水平，独立于β (2)- ar激活，降低激动剂诱导α (2B)- ar下调的EC50浓度，使用或不过度表达GRK2或GRK3（2- 10倍）的NG108细胞。在亲代NG108细胞中，α (2B)-AR下调所需的EPI EC50浓度为30 muM。然而，在NG108细胞中，GRK3过表达2- 3倍可将EC50降低至0.2 muM（降低150倍），而GRK2过表达可将其降低至1 muM（降低30倍）。然而，当GRK3或GRK2在NG108细胞中过表达8- 10倍时，α (2B)- ar下调的EC50浓度（0.02 ma EPI）降低了1000倍。这些数据清楚地表明，在EPI暴露后，适度上调GRK3（2- 3倍）比适度上调GRK2更有效地增强α (2B)- ar对下调的敏感性，但GRK2和GRK3在上调8- 10倍时诱导α (2B)- ar下调的效果相同。据我们所知，这是第一个系统地证明GRKs，特别是GRK3，在调节激动剂EC50浓度中起关键作用，从而下调α (2B)-AR，从而为已经复杂的信号网络增加了一个新的维度。
Chronic coactivation of alpha(2B)- and beta(2)-adrenoceptors (AR) was recently reported to down-regulate the alpha(2B)-AR at a lower threshold epinephrine (EPI) concentration compared with the activation of alpha(2B)-AR alone. This is the result of a modest beta(2)-AR-dependent up-regulation of G protein-coupled receptor kinase 3 (GRK3). In the present study, we determined that increasing GRK2 or GRK3 levels, independent of beta(2)-AR activation, decreases the EC50 concentration for agonist-induced down-regulation of the alpha(2B)-AR using NG108 cells with or without overexpression (2- to 10-fold) of GRK2 or GRK3. In parental NG108 cells, the EC50 concentration of EPI required for downregulation of the alpha(2B)-AR is 30 muM. A 2- to 3-fold overexpression of GRK3 in NG108 cells, however, reduces the EC50 to 0.2 muM ( a 150-fold decrease), whereas a comparable overexpression of GRK2 reduces it to 1 muM ( a 30-fold decrease). However, when GRK3 or GRK2 in NG108 cells are overexpressed 8- to 10-fold, the EC50 concentration (0.02 muM EPI) for alpha(2B)-AR down-regulation is reduced 1000-fold. These data clearly suggest that a modest (2- to 3-fold) up-regulation of GRK3 is more effective at enhancing the sensitivity of alpha(2B)-AR to down-regulation after exposure to EPI than a modest up-regulation of GRK2, but that both GRK2 and GRK3 are equally effective at inducing alpha(2B)-AR down-regulation when up-regulated 8- to 10-fold. To our knowledge, this is the first report to systematically demonstrate that GRKs, particularly GRK3, play a pivotal role in modulating the agonist EC50 concentration that down-regulates the alpha(2B)-AR and thus adds a new dimension to an already intricate signaling network.