期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：2
页码：602-606
DOI：10.1073/pnas.1423113112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceVoltage-gated calcium channels are essential for diverse cellular functions. For example, CaV1.1 channels trigger skeletal muscle contraction and CaV1.2 channels regulate neural gene expression in response to neuronal activity. Thus, it is important to understand the cellular mechanisms that regulate delivery of these channels to the plasma membrane and that govern calcium movements via the membrane-inserted channels. Here we show that the cellular adapter protein "Stac3" participates in both processes. Specifically, Stac3 binds to both CaV1.1 and CaV1.2. This binding is essential for efficient delivery of CaV1.1 to the plasma membrane, but not for CaV1.2. However, binding of Stac3, or the related protein Stac2, to CaV1.2 causes a dramatic slowing of inactivation, thereby increasing calcium entry via CaV1.2. Excitation-contraction (EC) coupling in skeletal muscle depends upon trafficking of CaV1.1, the principal subunit of the dihydropyridine receptor (DHPR) (L-type Ca2+ channel), to plasma membrane regions at which the DHPRs interact with type 1 ryanodine receptors (RyR1) in the sarcoplasmic reticulum. A distinctive feature of this trafficking is that CaV1.1 expresses poorly or not at all in mammalian cells that are not of muscle origin (e.g., tsA201 cells), in which all of the other nine CaV isoforms have been successfully expressed. Here, we tested whether plasma membrane trafficking of CaV1.1 in tsA201 cells is promoted by the adapter protein Stac3, because recent work has shown that genetic deletion of Stac3 in skeletal muscle causes the loss of EC coupling. Using fluorescently tagged constructs, we found that Stac3 and CaV1.1 traffic together to the tsA201 plasma membrane, whereas CaV1.1 is retained intracellularly when Stac3 is absent. Moreover, L-type Ca2+ channel function in tsA201 cells coexpressing Stac3 and CaV1.1 is quantitatively similar to that in myotubes, despite the absence of RyR1. Although Stac3 is not required for surface expression of CaV1.2, the principle subunit of the cardiac/brain L-type Ca2+ channel, Stac3 does bind to CaV1.2 and, as a result, greatly slows the rate of current inactivation, with Stac2 acting similarly. Overall, these results indicate that Stac3 is an essential chaperone of CaV1.1 in skeletal muscle and that in the brain, Stac2 and Stac3 may significantly modulate CaV1.2 function.
关键词：Stac adaptor protein ; L-type Ca2+ channel ; excitation–contraction coupling
