Regulation Of Kainate Receptors Research Articles

Protein Implicated in Nonsyndromic Mental Retardation Regulates Protein Kinase A (PKA) Activity

Mutation of the coiled-coil and C2 domain-containing 1A (CC2D1A) gene, which encodes a C2 domain and DM14 domain-containing protein, has been linked to severe autosomal recessive nonsyndromic mental retardation. Using a mouse model that produces a truncated form of CC2D1A that lacks the C2 domain and three of the four DM14 domains, we show that CC2D1A is important for neuronal differentiation and brain development. CC2D1A mutant neurons are hypersensitive to stress and have a reduced capacity to form dendrites and synapses in culture. At the biochemical level, CC2D1A transduces signals to the cyclic adenosine 3',5'-monophosphate (cAMP)-protein kinase A (PKA) pathway during neuronal cell differentiation. PKA activity is compromised, and the translocation of its catalytic subunit to the nucleus is also defective in CC2D1A mutant cells. Consistently, phosphorylation of the PKA target cAMP-responsive element-binding protein, at serine 133, is nearly abolished in CC2D1A mutant cells. The defects in cAMP/PKA signaling were observed in fibroblast, macrophage, and neuronal primary cells derived from the CC2D1A KO mice. CC2D1A associates with the cAMP-PKA complex following forskolin treatment and accumulates in vesicles or on the plasma membrane in wild-type cells, suggesting that CC2D1A may recruit the PKA complex to the membrane to facilitate signal transduction. Together, our data show that CC2D1A is an important regulator of the cAMP/PKA signaling pathway, which may be the underlying cause for impaired mental function in nonsyndromic mental retardation patients with CC2D1A mutation.

Regulation of the GABA cell phenotype in hippocampus of schizophrenics and bipolars

GABAergic dysfunction is present in the hippocampus in schizophrenia (SZ) and bipolar disorder (BD). The trisynaptic pathway was "deconstructed" into various layers of sectors CA3/2 and CA1 and gene expression profiling performed. Network association analysis was used to uncover genes that may be related to regulation of glutamate decarboxylase 67 (GAD(67)), a marker for this system that has been found by many studies to show decreased expression in SZs and BDs. The most striking change was a down-regulation of GAD(67) in the stratum oriens (SO) of CA2/3 in both groups; CA1 only showed changes in the SO of schizophrenics. The network generated for GAD(67) contained 25 genes involved in the regulation of kainate receptors, TGF-beta and Wnt signaling, as well as transcription factors involved in cell growth and differentiation. In SZs, IL-1beta, (GRIK2/3), TGF-beta2, TGF-betaR1, histone deacetylase 1 (HDAC1), death associated protein (DAXX), and cyclin D2 (CCND2) were all significantly up-regulated, whereas in BDs, PAX5, Runx2, LEF1, TLE1, and CCND2 were significantly down-regulated. In the SO of CA1 of BDs, where GAD67 showed no expression change, TGF-beta and Wnt signaling genes were all up-regulated, but other transcription factors showed no change in expression. In other layers/sectors, BDs showed no expression changes in these GAD(67) network genes. Overall, these results are consistent with the hypothesis that decreased expression of GAD(67) may be associated with an epigenetic mechanism in SZ. In BD, however, a suppression of transcription factors involved in cell differentiation may contribute to GABA dysfunction.

Long-Term Depression of Kainate Receptor-Mediated Synaptic Transmission

Kainate receptors (KARs) have been shown to be involved in hippocampal mossy fiber long-term potentiation (LTP); however, it is not known if KARs are involved in the induction or expression of long-term depression (LTD), the other major form of long-term synaptic plasticity. Here we describe LTD of KAR-mediated synaptic transmission (EPSC(KA) LTD) in perirhinal cortex layer II/III neurons that is distinct from LTD of AMPAR-mediated transmission, which also coexists at the same synapses. Induction of EPSC(KA) LTD requires a rise in postsynaptic Ca(2+) but is independent of NMDARs or T-type voltage-gated Ca(2+) channels; however, it requires synaptic activation of inwardly rectifying KARs and release of Ca(2+) from stores. The synaptic KARs are regulated by tonically activated mGluR5, and expression of EPSC(KA) LTD occurs via a mechanism involving mGluR5, PKC, and PICK1 PDZ domain interactions. Thus, we describe the induction and expression mechanism of a form of synaptic plasticity, EPSC(KA) LTD.

Regulation of kainate receptors by protein kinase C and metabotropic glutamate receptors

Kainate receptors have recently been shown to be involved in synaptic transmission, to regulate transmitter release and to mediate synaptic plasticity in different regions of the CNS. However, very little is known about endogenous mechanisms that can control native kainate receptor signalling. In this study we have found that GluR5-containing kainate receptor-mediated actions can be modulated by activation of protein kinase C (PKC) but not protein kinase A (PKA). However, both PKA and PKC directly phosphorylate the GluR5 subunit of kainate receptors. Metabotropic glutamate (mGlu) receptors are well known to be involved in synaptic transmission, regulation of transmitter release and synaptic plasticity in a variety of brain regions. We now demonstrate that kainate receptor signalling is enhanced by activation of group I mGlu receptors, in a PKC-dependent manner. These data demonstrate for the first time that kainate receptor function can be modulated by activation of metabotropic glutamate receptors and have implications for understanding mechanisms of synaptic transmission, plasticity and disorders such as epilepsy.

Regulation of kainate receptors by protein kinase C and metabotropic glutamate receptors.

Kainate receptors have recently been shown to be involved in synaptic transmission, to regulate transmitter release and to mediate synaptic plasticity in different regions of the CNS. However, very little is known about endogenous mechanisms that can control native kainate receptor signalling. In this study we have found that GluR5-containing kainate receptor-mediated actions can be modulated by activation of protein kinase C (PKC) but not protein kinase A (PKA). However, both PKA and PKC directly phosphorylate the GluR5 subunit of kainate receptors. Metabotropic glutamate (mGlu) receptors are well known to be involved in synaptic transmission, regulation of transmitter release and synaptic plasticity in a variety of brain regions. We now demonstrate that kainate receptor signalling is enhanced by activation of group I mGlu receptors, in a PKC-dependent manner. These data demonstrate for the first time that kainate receptor function can be modulated by activation of metabotropic glutamate receptors and have implications for understanding mechanisms of synaptic transmission, plasticity and disorders such as epilepsy.

124. Differential expression of 5-HT receptor mRNA by AMPA and kainate receptor regulation in brain

124. Differential expression of 5-HT receptor mRNA by AMPA and kainate receptor regulation in brain

Regulation of kainate receptors by cAMP-dependent protein kinase and phosphatases.

In the mammalian central nervous system, receptors for excitatory amino acid neurotransmitters such as the alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA)-kainate receptor mediate a large fraction of excitatory transmission. Currents induced by activation of the AMPA-kainate receptor were potentiated by agents that specifically stimulate adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase A (PKA) activity or were supported by intracellular application of the catalytic subunit of PKA by itself or in combination with cAMP. Furthermore, depression of these currents by a competitive inhibitor of PKA indicates that AMPA-kainate receptors are regulated by endogenous PKA. Endogenous protein phosphatases also regulate these receptors because an inhibitor of cellular phosphates enhanced kainate currents. Modulation of PKA and phosphatases may regulate the function of these receptors and thus contribute to synaptic plasticity in hippocampal neurons.