Regulation of the Ca2+/CaM-Responsive Pool of CaMKII by Scaffold-Dependent Autophosphorylation

Abstract

CaMKII is critical for structural and functional plasticity. Here we show that Camguk (Cmg), the Drosophila homolog of CASK/Lin-2, associates in an ATP-regulated manner with CaMKII to catalyze formation of a pool of calcium-insensitive CaMKII. In the presence of Ca(2+)/CaM, CaMKII complexed to Cmg can autophosphorylate at T287 and become constitutively active. In the absence of Ca(2+)/CaM, ATP hydrolysis results in phosphorylation of T306 and inactivation of CaMKII. Cmg coexpression suppresses CaMKII activity in transfected cells, and the level of Cmg expression in Drosophila modulates postsynaptic T306 phosphorylation. These results suggest that Cmg, in the presence of Ca(2+)/CaM, can provide a localized source of active kinase. When Ca(2+)/CaM or synaptic activity is low, Cmg promotes inactivating autophosphorylation, producing CaMKII that requires phosphatase to reactivate. This interaction provides a mechanism by which the active postsynaptic pool of CaMKII can be controlled locally to differentiate active and inactive synapses.

Protein Phosphatases and Calcium/Calmodulin-Dependent Protein Kinase II-Dependent Synaptic Plasticity: Figure 1.

“…Although these studies did not specifically identify the phosphatase activity (Weeber et al, 2003), the phosphopeptide substrate used is generally considered PP2A selective. Interestingly, recent work in Drosophila provided genetic evidence for PP2A-mediated dephosphorylation of Thr 306 (equivalent to Thr 305 in mammalian CaMKII) in vivo (Lu et al, 2003). If PP2A also dephosphorylates Thr 305 and Thr 306 in mammals, it is possible that reduced PP2A activity in the mouse model of Angelman's syndrome results in enhanced CaMKII autophosphorylation at Thr 305/306 and/or Thr 286 .…”

αCaMKII autophosphorylation levels differ depending on subcellular localization

“…In addition, T305/6 phosphorylation increases the dissociation rate of CaMKII from the PSD (Shen et al, 2000), and mimicking phosphorylation on these residues prevents while inhibiting phosphorylation enhances PSD association of the kinase (Elgersma et al, 2002). Furthermore, CaMKII interaction with NR2B, which is enriched at the PSD, has been shown to suppress T305/6 phosphorylation (Bayer et al, 2001), and T306 phosphorylation leads to CaMKII dissociation from the synapse associated protein Camguk in Drosophila (Lu et al, 2003). These studies suggest that phosphorylation of T305/6 is an important inhibitory mechanism controlling αCaMKII association with the PSD, and that αCaMKII localized at the PSD is most likely less phosphorylated on T305/6 than αCaMKII in other parts of the neuron.…”

Deletion of CASK in mice is lethal and impairs synaptic function

“…Moreover, analysis of CASK mutations in Drosophila melanogaster and C. elegans suggested several other functions. In Drosophila, CASK mutations produce a discrete neurological phenotype that includes aberrant regulation of activities mediated by calcium/calmodulin-dependent kinase II (15,16), and CASK may function by modulating Ca 2ϩ -calmodulin dependent protein kinase (17). In contrast, in C. elegans the CASK homolog Lin-2 is selectively required for vulval differentiation and proper localization of the EGF receptor LET-23 (5).…”