Protein Kinase C Activation Modulates α-Calmodulin Kinase II Binding to NR2A Subunit of N-Methyl-D-Aspartate Receptor Complex

The N-methyl-d-aspartate (NMDA) receptor subunits NR2 possess extended intracellular C-terminal domains by which they can directly interact with a large number of postsynaptic density (PSD) proteins involved in synaptic clustering and signaling. We have previously shown that PSD-associated alpha-calmodulin kinase II (alphaCaMKII) binds with high affinity to the C-terminal domain of the NR2A subunit. Here, we show that residues 1412-1419 of the cytosolic tail of NR2A are critical for alphaCaMKII binding, and we identify, by site directed mutagenesis, PKC-dependent phosphorylation of NR2A(Ser(1416)) as a key mechanism in inhibiting alphaCaMKII-binding and promoting dissociation of alphaCaMKII.NR2A complex. In addition, we show that stimulation of PKC activity in hippocampal slices either with phorbol esters or with the mGluRs specific agonist trans-1-amino-1,3- cyclopentanedicarboxylic acid (t-ACPD) decreases alphaCaMKII binding to NMDA receptor complex. Thus, our data provide clues on understanding the molecular basis of a direct cross-talk between alphaCaMKII and PKC pathways in the postsynaptic compartment

Differential translocation of protein kinase C isozymes in rats characterized by a chronic lack of LTP induction and cognitive impairment

AbstractThe translocation of protein kinase C isozymes was investigated in an animal model of cognitive deficit and lack of induction of long-term potentiation (LTP). In MAM rats, presynaptic α, β, ϵ PKC showed enhanced translocation, while postsynaptic γ PKC displayed decreased translocation when compared to control levels. This imbalance of PKC isozyme translocation between the pre- and post-synaptic compartment might therefore represent a possible molecular cause for the lack of synaptic plasticity observed in these animals

Distribution of interleukin-1 receptor complex at the synaptic membrane driven by interleukin-1β and NMDA stimulation

Interleukin-1β (IL-1β) is a pro-inflammatory cytokine that contributes to neuronal injury in various degenerative diseases, and is therefore a potential therapeutic target. It exerts its biological effect by activating the interleukin-1 receptor type I (IL-1RI) and recruiting a signalling core complex consisting of the myeloid differentiation primary response protein 88 (MyD88) and the IL-1R accessory protein (IL-1RAcP). This pathway has been clearly described in the peripheral immune system, but only scattered information is available concerning the molecular composition and distribution of its members in neuronal cells. The findings of this study show that IL-1RI and its accessory proteins MyD88 and IL-1RAcP are differently distributed in the hippocampus and in the subcellular compartments of primary hippocampal neurons. In particular, only IL-1RI is enriched at synaptic sites, where it co-localises with, and binds to the GluN2B subunit of NMDA receptors. Furthermore, treatment with NMDA increases IL-1RI interaction with NMDA receptors, as well as the surface expression and localization of IL-1RI at synaptic membranes. IL-1β also increases IL-1RI levels at synaptic sites, without affecting the total amount of the receptor in the plasma membrane. Our results reveal for the first time the existence of a dynamic and functional interaction between NMDA receptor and IL-1RI systems that could provide a molecular basis for IL-1β as a neuromodulator in physiological and pathological events relying on NMDA receptor activation

The l-histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity is a general response in cultured mammalian cell lines and is always associated with the formation of DNA double strand breaks

AbstractMicromolar concentrations of l-histidine increase the cytotoxicity of hydrogen peroxide in a number of cell lines including CHO(hamster), EAHY, McCoy's, U937 and CCRF-CEM (human), Vero (monkey) and SC-1 (mouse). Importantly, these cell lines displayed differentt degrees of sensitivity to H2O2 alone and the extent of enhancement elicited by the amino acid was more pronounced in resistant cell lines. The increased cytotoxicity was invariably associated with the formation of DNA DSBs and a remarkable correlation was found by plotting the level of DNA DSBs against the cytotoxic response. These results strongly support the hypothesis that the mechanism whereby l-histidine increases the toxicity elicited by H2O2 involves the formation of DNA DSBs and are consistent with the possibility that the amino acid might participate in the regulation of the physio-pathological response to oxidative stress in mammals

Chapter 27 Signalling mechanisms involved in P2Y receptor-mediated reactive astrogliosis

Transductional studies have suggested that the P2Y receptor signaling to the nucleus occurs through an early release of AA and induction of the fos and jun gene products, likely via the PKC/MAPK pathway or through a yet-to-be determined intracellular pathway involving products of arachidonate metabolism. Formation of Fos and Jun heterodimers upon challenge of astroglial cells with ATP has been suggested by Neary; these complexes may affect the transcription of genes specifically involved in the gliotic reaction. A new field concerns the identification of the molecules that specifically contribute to purine-induced reactive astrogliosis and it is anticipated that in the next few years several researchers will focus their attention on this intriguing topic. The finding that ATP has a role in reactive astrogliosis may also disclose novel therapeutic approaches to the modulation of post-traumatic and post-ischemic brain repair. In particular, recent data demonstrating induction of COX-2 in astrocytes upon stimulation of the gliotic P2Y receptor (Brambilla et al.,) may have intriguing implications in the therapy of neurological disorders characterized by excessive astroglial reaction and inflammation