Regulation of NMDA Receptor Activity by F-Actin and Myosin Light Chain Kinase

Abstract

The postsynaptic density (PSD) at excitatory dendritic synapses comprises a protein complex of glutamate receptors, scaffolding elements, and signaling enzymes. For example, NMDA receptors (NMDARs) are linked to several proteins in the PSD, such as PSD-95, and are also tethered via binding proteins such as alpha-actinin directly to filamentous actin of the cytoskeleton. Depolymerization of the cytoskeleton modulates the activity of NMDARs, and, in turn, strong activation of NMDARs can trigger depolymerization of actin. Myosin, the motor protein of muscular contraction and nonmuscle motility, is also associated with NMDARs and the PSD. We show here that constitutively active myosin light chain kinase (MLCK) enhances NMDAR-mediated whole-cell and synaptic currents in acutely isolated CA1 pyramidal and cultured hippocampal neurons, whereas inhibitors of MLCK depress these currents. This MLCK-dependent regulation was observed in cell-attached patches but was lost after excision to inside-out patches. Furthermore, the enhancement induced by constitutively active MLCK and the depression of MLCK inhibitors were eliminated after depolymerization of the cytoskeleton. NMDARs and MLCK did not colocalize in clusters on the dendrites of cultured hippocampal neurons, further indicating that the effects of MLCK are mediated indirectly via actomyosin. Our results suggest that MLCK enhances actomyosin contractility to either increase the membrane tension on NMDARs or to alter physical relationships between the actin cytoskeleton and the linker proteins of NMDARs.

Glutamatergic Signaling Maintains the Epithelial Phenotype of Proximal Tubular Cells

“…Being aware of the existence of biochemical and functional interactions between NMDAR subunits and cytoskeletal proteins, 34,35 we sought to examine the influence of NMDAR activation on migration and F-actin distribution in HK-2. We showed by two independent in vitro migration assays that the activation of NMDAR has an inhibitory effect on cell migration.…”

PDZ Domain-mediated Interaction of Interleukin-16 Precursor Proteins with Myosin Phosphatase Targeting Subunits

“…It has been shown in this context that a PDZ-mediated NMDA-postsynaptic density 95 com- plex is linked to myosin V and dynein by the guanylate kinase domain-associated protein (47). Moreover, the activity of NMDA receptors is regulated by F-actin and myosin light chain kinase, indicating a regulatory function for the myosin phosphatase as well (48). A complex of myosin phosphatase targeting subunits, npro-IL-16 and ion channels, raises the possibility that the interactions play a role in the processes of ion channel trafficking or positioning in the cortical cytoskeleton at the plasma membrane mentioned above.…”

Dysfunctional synapse in Alzheimer's disease – A focus on NMDA receptors

“…Moreover, cofilin, an actin depolymerizing factor which links actin and PIP 2 is required for NMDARs regulation, suggesting that a decrease in PIP 2 leads to cofilin release and actin depolymerization, which in turn promotes NMDARs internalization (Mandal and Yan, 2009). Active myosin light chain kinase enhances NMDARs-mediated whole-cell and synaptic currents, increasing actin-myosin contractility, which leads to increased membrane tension on NMDARs or to altered physical relationships between NMDAR anchored proteins, such as PSD-95 (Kornau et al, 1995) and cytoskeleton (Lei et al, 2001). …”