Li Yan, Sroubek Jakub, Krishnan Yamini, McDonald Thomas V
Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
J Membr Biol. 2008 May;223(2):107-16. doi: 10.1007/s00232-008-9118-4. Epub 2008 Aug 5.
Adrenergic stimulation of the heart initiates a signaling cascade in cardiac myocytes that increases the concentration of cAMP. Although cAMP elevation may occur over a large area of a target-organ cell, its effects are often more restricted due to local concentration of its main effector, protein kinase A (PKA), through A-kinase anchoring proteins (AKAPs). The HERG potassium channel, which produces the cardiac rapidly activating delayed rectifying K+ current (I(Kr)), is a target for cAMP/PKA regulation. PKA regulation of the current may play a role in the pathogenesis of hereditary and acquired abnormalities of the channel leading to cardiac arrhythmia. We examined the possible role for AKAP-mediated regulation of HERG channels. Here, we report that the PKA-RII-specific AKAP inhibitory peptide AKAP-IS perturbs the distribution of PKA-RII and diminishes the PKA-dependent phosphorylation of HERG protein. The functional consequence of AKAP-IS is a reversal of cAMP-dependent regulation of HERG channel activity. In further support of AKAP-mediated targeting of kinase to HERG, PKA activity was coprecipitated from HERG expressed in HEK cells. Velocity gradient centrifugation of solubilized porcine cardiac membrane proteins showed that several PKA-RI and PKA-RII binding proteins cosediment with ERG channels. A physical association of HERG with several specific AKAPs with known cardiac expression, however, was not demonstrable in heterologous cotransfection studies. These results suggest that one or more AKAP(s) targets PKA to HERG channels and may contribute to the acute regulation of I(Kr) by cAMP.
心脏的肾上腺素能刺激在心肌细胞中引发信号级联反应，增加环磷酸腺苷（cAMP）的浓度。尽管cAMP升高可能发生在靶器官细胞的大面积区域，但由于其主要效应物蛋白激酶A（PKA）通过A激酶锚定蛋白（AKAPs）进行局部浓度调节，其作用往往更具局限性。产生心脏快速激活延迟整流钾电流（I(Kr)）的人类ether-à-go-go相关基因（HERG）钾通道是cAMP/PKA调节的靶点。PKA对该电流的调节可能在导致心律失常的该通道遗传性和获得性异常的发病机制中起作用。我们研究了AKAP介导的HERG通道调节的可能作用。在此，我们报告PKA-RII特异性AKAP抑制肽AKAP-IS扰乱了PKA-RII的分布，并减少了HERG蛋白的PKA依赖性磷酸化。AKAP-IS的功能后果是HERG通道活性的cAMP依赖性调节的逆转。为进一步支持AKAP介导的激酶靶向HERG，从在人胚肾（HEK）细胞中表达的HERG中共沉淀出PKA活性。对溶解的猪心脏膜蛋白进行速度梯度离心显示，几种PKA-RI和PKA-RII结合蛋白与ERG通道共沉降。然而，在异源共转染研究中未证实HERG与几种已知在心脏中表达的特定AKAPs存在物理关联。这些结果表明，一种或多种AKAP将PKA靶向HERG通道，并可能有助于cAMP对I(Kr)的急性调节。
