Cyclin-Dependent Kinase 5 Regulates PSD-95 Ubiquitination in Neurons

Abstract

The kinase Cdk5 and its activator p35 have been implicated in drug addiction, neurodegenerative diseases such as Alzheimer’s, learning and memory, and synapse maturation and plasticity. However the molecular mechanisms by which Cdk5 regulates synaptic plasticity are still unclear. PSD-95 is a major postsynaptic scaffolding protein of glutamatergic synapses that regulates synaptic strength and plasticity. PSD-95 is ubiquitinated by the Ubiquitin E3 Ligase Mdm2, and rapid and transient PSD-95 ubiquitination has been implicated in NMDA receptor-induced AMPA receptor endocytosis. Here we demonstrate that genetic or pharmacological reduction of Cdk5 activity increases the interaction of Mdm2 with PSD-95 and enhances PSD-95 ubiquitination without affecting PSD-95 protein levels in vivo in mice, suggesting a non-proteolytic function of ubiquitinated PSD-95 at synapses. We show that PSD-95 ubiquitination correlates with increased interaction with β-adaptin, a subunit of the clathrin adaptor protein complex AP-2. This interaction is increased by genetic reduction of Cdk5 activity or NMDA receptor stimulation and is dependent on Mdm2. Together these results support a function for Cdk5 in regulating PSD-95 ubiqutination and its interaction with AP-2 and suggest a mechanism by which PSD-95 may regulate NMDA receptor-induced AMPA receptor endocytosis.

Low Density Lipoprotein Receptor-related Protein 1 (LRP1) Modulates N-Methyl-d-aspartate (NMDA) Receptor-dependent Intracellular Signaling and NMDA-induced Regulation of Postsynaptic Protein Complexes

“…In contrast to Colledge et al (25), we found that, at least in our experimental system, NMDA-induced PSD-95 degradation was not proteasome-dependent because it could not be prevented by a variety of proteasome inhibitors. This is in line with the findings of Bianchetta et al (26), who did not find proteasomal degradation of PSD-95 and suggested a non-proteolytical regulatory function for ubiquitinated PSD-95 in the regulation of NMDAinduced AMPA receptor endocytosis. Still, NMDA-induced degradation of PSD-95 was impaired in the absence of LRP1 (Fig.…”

Palmitoylation of Superoxide Dismutase 1 (SOD1) Is Increased for Familial Amyotrophic Lateral Sclerosis-linked SOD1 Mutants

“…Proteins were eluted with 0.1 M glycine-HCl buffer, pH 2.1, and then enzymatically digested with Glu-C to ensure that cysteine-containing peptides were of proper length (ϳ500 -3000 Da) for optimum MS/MS by high energy collisional dissociation fragmentation in a Hybrid Orbitrap Elite MS system. Similar LC MS/MS were carried out as described previously (39). Collected MS and MS/MS data were peak-picked with MASCOT Distiller and searched against the Swiss Prot Human protein database utilizing an in-house MASCOT algorithm (version 2.2.0).…”

The Role of Cdk5 in Alzheimer’s Disease

“…Preliminary findings have already shown that Cdk5 is also pivotal to postsynaptic compartment, where exists a lot of substrates of Cdk5, such as NMDAR [90], PSD-95 [91], DARPP-32 [42], and dopamine D2 receptor [33]. Cdk5 can modulate the function of NMDAR, which is related to the induction of some forms of synaptic plasticity; for example, the NMDAR-dependent Hebbian long-term potentiation (LTP) and long-term depression (LTD).…”

“…Also, an inhibition of Cdk5 displays an enhancement of learning and plasticity owning to an increased NR2B levels at the synapse triggered by disturbing calpain/ NR2B complex [90]. Moreover, Cdk5 mediates the regulation of the scaffold protein PSD-95 expression, which can fasten NMDA receptors to the postsynaptic density [91]. The scaffold protein PSD-95, prime ingredient of postsynaptic density, is known to transfer signal to neurotransmitter receptors.…”