Gangopadhyay Samudra S, Gallant Cynthia, Sundberg Eric J, Lane William S, Morgan Kathleen G
Department of Health Sciences, Sargent College, Boston University, 635 Commonwealth Avenue, Boston, MA 02215, USA.
Biochem J. 2008 Jun 15;412(3):507-16. doi: 10.1042/BJ20071582.
We present here the identification and characterization of an SCP3 (small C-terminal domain phosphatase-3) homologue in smooth muscle and show, for the first time, that it dephosphorylates CaMKII [Ca(2+)/CaM (calmodulin)-dependent protein kinase II]. SCP3 is a PP2C (protein phosphatase 2C)-type phosphatase that is primarily expressed in vascular smooth muscle tissues and specifically binds to the association domain of the CaMKIIgamma G-2 variant. The dephosphorylation is site-specific, excluding the Thr(287) associated with Ca(2+)/CaM-independent activation of the kinase. As a result, the autonomous activity of CaMKIIgamma G-2 is not affected by the phosphatase activity of SCP3. SCP3 co-localizes with CaMKIIgamma G-2 on cytoskeletal filaments, but is excluded from the nucleus in differentiated vascular smooth muscle cells. Upon depolarization-induced Ca(2+) influx, CaMKIIgamma G-2 is activated and dissociates from SCP3. Subsequently, CaMKIIgamma G-2 is targeted to cortical adhesion plaques. We show here that SCP3 regulates phosphorylation sites in the catalytic domain, but not those involved in regulation of kinase activation. This selective dephosphorylation by SCP3 creates a constitutively active kinase that can then be differentially regulated by other phosphorylation-dependent regulatory mechanisms.
我们在此展示了平滑肌中SCP3（小C末端结构域磷酸酶-3）同源物的鉴定与特性，并首次表明它可使CaMKII[Ca(2+)/CaM（钙调蛋白）依赖性蛋白激酶II]去磷酸化。SCP3是一种PP2C（蛋白磷酸酶2C）型磷酸酶，主要在血管平滑肌组织中表达，并特异性结合CaMKIIγ G-2变体的结合结构域。这种去磷酸化是位点特异性的，不包括与激酶的Ca(2+)/CaM非依赖性激活相关的苏氨酸(287)。因此，CaMKIIγ G-2的自主活性不受SCP3磷酸酶活性的影响。SCP3与CaMKIIγ G-2在细胞骨架丝上共定位，但在分化的血管平滑肌细胞中被排除在细胞核外。在去极化诱导的Ca(2+)内流时，CaMKIIγ G-2被激活并与SCP3解离。随后，CaMKIIγ G-2靶向皮质黏附斑。我们在此表明，SCP3调节催化结构域中的磷酸化位点，但不调节参与激酶激活调节的位点。SCP3的这种选择性去磷酸化产生了一种组成型活性激酶，然后它可以通过其他磷酸化依赖性调节机制进行差异调节。
