Local Ca2+ Signals within Caveolae Cause Nuclear Translocation of CaMK1a in Mouse Vascular Smooth Muscle Cells

An increase in intracellular Ca2+ concentration ([Ca2+](i)) activates Ca2+-sensitive enzymes such as Ca2+/ calmodulin-dependent kinases (CaMK) and induces gene transcription in various types of cells. This signaling pathway is called excitation-transcription (E-T) coupling. Recently, we have revealed that a L-type Ca2+ channel/CaMK kinase (CaMKK) 2/CaMK1a complex located within caveolae in vascular smooth muscle cells (SMCs) can convert [Ca2+] i changes to gene transcription profiles that are related to chemotaxis. Although CaMK1a is expected to be the key molecular identity that can transport Ca2+ signals originated within caveolae to the nucleus, data sets directly proving this scheme are lacking. In this study, multicolor fluorescence imaging methods were utilized to address this question. Live cell imaging using mouse primary aortic SMCs revealed that CaMK1a can translocate from the cytosol to the nucleus; and that this movement was blocked by nifedipine or a CaMKK inhibitor, STO609. Experiments using two types of Ca2+ chelators, ethylene glyco l-bis(2-aminoethylether)-N,N, N',N'-tetraacetic acid (EGTA) and 1,2-bis(2- aminophenoxy)-ethane-N,N,N', N'- tetraacetic acid ( BAPTA), combined with caveolin-1 knockout (cav1-KO) mice showed that local Ca2+ events within c aveolae are required to trigger this C aMK1a nuclear translocation. Importantly, overexpression of cav1 in isolated cav1-KO myocytes recovered the CaMK1a translocation. In SMCs freshly isolated from mesenteric arteries, CaMK1a was localized mainly within caveolae in the resting state. Membrane depolarization induced both nuclear translocation and phosphorylation of CaMK1a. These responses were inhibited by nifedipine, STO609, cav1-KO, or BAPTA. These new findings strongly suggest that CaMK1a can transduce Ca2+ signaling generated within or very near caveolae to the nucleus and thus, promote E-T coupling.

Automated summary

This study reveals the existence of a complex located within caveolae in vascular smooth muscle cells that can convert changes in intracellular calcium concentrations to gene transcription profiles related to chemotaxis. CaMK1a is believed to be the key molecular identity that can transport calcium signals from caveolae to the nucleus.