Regulation of NMDA receptors by cyclin-dependent kinase-5

Abstract

Members of the N-methyl-D-aspartate (NMDA) class of glutamate receptors (NMDARs) are critical for development, synaptic transmission, learning and memory; they are targets of pathological disorders in the central nervous system. NMDARs are phosphorylated by both serine͞threonine and tyrosine kinases. Here, we demonstrate that cyclin dependent kinase-5 (Cdk5) associates with and phosphorylates NR2A subunits at Ser-1232 in vitro and in intact cells. Moreover, we show that roscovitine, a selective Cdk5 inhibitor, blocks both long-term potentiation induction and NMDAevoked currents in rat CA1 hippocampal neurons. These results suggest that Cdk5 plays a key role in synaptic transmission and plasticity through its up-regulation of NMDARs. The N-methyl-D-aspartate (NMDA) class of glutamate receptors (NMDAR) are essential for learning, memory, and development in the central nervous system (1-5). NMDARs are multimeric complexes formed from both NMDA receptor subunit (NR1) and modulatory NR2 subunits (6-9). A single gene encodes the NR1 subunit. Eight possible alternative RNA-splice variants provide molecular diversity of NMDARs (10). NR2A-NR2D are encoded by four separate genes (11,12). NMDARs consist of NR1͞NR2 heteromeric complexes (13-15). The activation of NMDARs and the influx of Ca NMDA-channel activity is dynamically modulated in both intracellular and extracellular sites (3). Phosphorylation sites have been identified on the NR1, NR2A, and NR2B subunits, but not on the NR2C-NR2D subunits. Protein kinase C phosphorylates Ser-890 and Ser-896, and protein kinase A phosphorylates Ser-897 within the C1 exon of the NR1 subunit (17-19). Calcium͞calmodulin protein kinase II mediates phosphorylation of NR2B, but not NR2A (20). More recently, phosphorylation at tyrosine residues of NR2A and NR2B has been described as an important determinant for NMDAR functions (19)(20). In particular, Fyn, a member of the Src family of nonreceptor protein tyrosine kinases, was shown to phosphorylate the NR2A (7, 21-23). However, no information is available concerning which kinases phosphorylate NR2A at serine͞threonine sites. Cyclindependent kinase-5 (Cdk5) is a serine͞threonine kinase that is activated by neuron-specific p35 and p39 proteins (24-27). It exists as a large, multimeric complex associated with cytoskeletal proteins in the neurons. Cdk5 has been shown to phosphorylate a wide variety of proteins, all of which have serine͞threonine sites in (K͞RT͞SPXK)-type motifs (28,29). A number of synaptic proteins have been identified as Cdk5 substrates (30-32). Cdk5 and p35, predominantly expressed in postmitotic neurons, play essential roles in neuronal migration, neurite outgrowth, and laminar configuration of the cerebral cortex (25,27,33). Cdk5 in association with p25, a truncated form of p35, hyperphosphorylates the microtubule-associated protein tau. This hyperphosphorylation is thought to disrupt the neuronal cytoskeleton and ultimately contributes to neurodegeneration in Alzheimer's disease (34).Because of its virtue of phosphoryl...

Cyclin-dependent kinase 5 regulates dopaminergic and glutamatergic transmission in the striatum

“…In agreement with our results, roscovitine had no effect on AMPA-mediated excitatory postsynaptic potentials in the CA1 area of the hippocampus (24). However, longer (35 min) application of CDK5 inhibitors produced a delayed increase in AMPA-mediated responses through the modulation of calcium-channel activity (25).…”

“…The ability of CDK5 to regulate dopamine release may explain the difference in the effect of roscovitine on NMDA currents in the striatum and in the hippocampus, where the dopamine levels are much lower and roscovitine decreases extrasynaptically activated NMDA currents. Such a depressant effect presumably results from inhibition of CDK5-mediated phosphorylation of the NMDA receptor subunit NR2A (24). This observation constitutes an additional difference with the striatum where the NR2A subunit is expressed at low levels (19,20) and probably does not account for the majority of functional NMDA receptors.…”

Cyclin-dependent Kinase-5 Is Involved in Neuregulin-dependent Activation of Phosphatidylinositol 3-Kinase and Akt Activity Mediating Neuronal Survival

“…Moreover, neuregulin induced Cdk5 activation in myotubes that correlated with the expression of acetylcholine receptor. Cdk5 has been implicated in synaptic function in other systems, phosphorylating components of the presynaptic complex or the postsynaptic receptor (7,11,12). Our results suggest that the neuregulin/ErbB receptor signal cascade that regulates neuronal survival is another important site for Cdk5 modulation.…”

“…Recently, Cdk5 has been suggested as contributing to the control of neuronal positioning in Reelin signaling during neural development (5) and to mediate neuronal guidance by regulating semaphorin-3A with Fyn kinase (6). Cdk5 and p35 have recently also been shown to regulate presynaptic and postsynaptic activity by phosphorylating Munc-18, amphiphysin, and the NR2A subunit of the N-methyl-D-aspartate receptor (7)(8)(9)(10)(11). Cdk5 activity also regulates dopamine signaling by phosphorylating DARPP-32 protein (12) and has been shown to up-regulate the expression of acetylcholine receptor at the neuromuscular junction (13).…”

Cocaine-induced proliferation of dendritic spines in nucleus accumbens is dependent on the activity of cyclin-dependent kinase-5

“…Dendritic spines are highly responsive to fluctuations in dopaminergic and glutamatergic transmission (Meredith et al, 1995;Segal and Andersen, 2000;Robinson et al, 2001). Postsynaptically, Cdk5 can modulate D1/cAMP/PKA/DARPP-32 intracellular signaling and regulate NMDA receptor function (Bibb et al, 1999a,b;Li et al, 2001). Roscovitine may therefore impact cocaine-induced spine proliferation and normal spine maintenance by altering spine actin dynamics, intracellular signaling cascades, or glutamatergic and/or dopaminergic neurotransmission.…”