Department of Pharmacology, University of California San Diego, CA, USA.
Circ Res. 2011 Dec 9;109(12):1354-62. doi: 10.1161/CIRCRESAHA.111.248401. Epub 2011 Oct 13.
Differential effects of δ(B) and δ(C) subtypes of Ca²⁺/calmodulin-dependent protein kinase (CaMKII) on cardiomyocyte Ca²⁺ handling and survival have been suggested to result from their respective nuclear versus cytosolic localizations. CaMKIIδ subtype localization and its relationship to enzyme activation and target phosphorylation have not, however, been systematically evaluated.
To determine whether CaMKIIδ subtypes are restricted to a particular subcellular location and assess the relationship of localization to enzyme activation and function.
CaMKIIδ is highly expressed in mouse heart and cardiomyocytes and concentrated in sarcoplasmic reticulum (SR)/membrane and nuclear fractions. CaMKIIδ(B) and δ(C) subtypes differ by a nuclear localization sequence, but both are present in nuclear and SR/membrane fractions. Nonselective subtype distribution is also seen in mice overexpressing CaMKIIδ(B) or δ(C), even in a CaMKIIδ null background. Fluorescently tagged CaMKIIδ(B) expressed in cardiomyocytes concentrates in nuclei whereas δ(C) concentrates in cytosol, but neither localization is exclusive. Mouse hearts exposed to phenylephrine show selective CaMKIIδ activation in the nuclear (versus SR) compartment, whereas caffeine selectively activates CaMKIIδ in SR (versus nuclei), independent of subtype. Compartmentalized activation extends to functional differences in target phosphorylation at CaMKII sites: phenylephrine increases histone deacetylase 5 phosphorylation (Ser498) but not phospholamban (Thr17), whereas the converse holds for caffeine.
These studies demonstrate that CaMKIIδ(B) and δ(C) are not exclusively restricted to the nucleus and cytosol and that spatial and functional specificity in CaMKIIδ activation is elicited by mobilization of different Ca²⁺ stores rather than by compartmentalized subtype localization.
δ(B)和δ(C)亚型的钙/钙调蛋白依赖性蛋白激酶 (CaMKII) 的作用不同，对心肌细胞 Ca²⁺处理和存活的影响被认为是由于它们各自的核内和细胞质定位。然而，CaMKIIδ 亚基的定位及其与酶激活和靶磷酸化的关系尚未得到系统评估。
确定 CaMKIIδ 亚型是否局限于特定的亚细胞位置，并评估定位与酶激活和功能的关系。
CaMKIIδ 在小鼠心脏和心肌细胞中高度表达，并集中在肌浆网 (SR)/膜和核部分。CaMKIIδ(B)和δ(C)亚型通过核定位序列不同，但均存在于核和 SR/膜部分。在过表达 CaMKIIδ(B)或δ(C)的小鼠中也观察到非选择性亚型分布，即使在 CaMKIIδ 缺失的背景下也是如此。在心肌细胞中表达的荧光标记 CaMKIIδ(B)集中在核内，而 δ(C)集中在细胞质中，但没有一种定位是排他性的。用苯肾上腺素处理的小鼠心脏显示 CaMKIIδ 在核 (相对于 SR) 区室中的选择性激活，而咖啡因选择性地在 SR (相对于核) 中激活 CaMKIIδ，而与亚型无关。分区激活扩展到 CaMKII 位点靶磷酸化的功能差异：苯肾上腺素增加组蛋白去乙酰化酶 5 的磷酸化 (Ser498)，但不增加磷酸化酶 (Thr17)，而咖啡因则相反。
这些研究表明，CaMKIIδ(B)和δ(C)并非仅局限于核和细胞质，CaMKIIδ 的空间和功能特异性激活是通过动员不同的 Ca²⁺库而不是通过分区亚型定位来引发的。
