Status epilepticus alters hippocampal PKAbeta and PKAgamma expression in mice

Metabotropic Glutamate Receptors and Interacting Proteins in Epileptogenesis

Neurotransmitter and receptor systems are involved in different neurological and neuropsychological disorders such as Parkinson's disease, depression, Alzheimer’s disease and epilepsy. Recent advances in studies of signal transduction pathways or interacting proteins of neurotransmitter receptor systems suggest that different receptor systems may share the common signal transduction pathways or interacting proteins which may be better therapeutic targets for development of drugs to effectively control brain diseases. In this paper, we reviewed metabotropic glutamate receptors (mGluRs) and their related signal transduction pathways or interacting proteins in status epilepticus and temporal lobe epilepsy, and proposed some novel therapeutical drug targets for controlling epilepsy and epileptogenesis.

GABAB receptor phosphorylation regulates KCTD12-induced K⁺ current desensitization

GABAB receptors assemble from GABAB1 and GABAB2 subunits. GABAB2 additionally associates with auxiliary KCTD subunits (named after their K(+) channel tetramerization-domain). GABAB receptors couple to heterotrimeric G-proteins and activate inwardly-rectifying K(+) channels through the βγ subunits released from the G-protein. Receptor-activated K(+) currents desensitize in the sustained presence of agonist to avoid excessive effects on neuronal activity. Desensitization of K(+) currents integrates distinct mechanistic underpinnings. GABAB receptor activity reduces protein kinase-A activity, which reduces phosphorylation of serine-892 in GABAB2 and promotes receptor degradation. This form of desensitization operates on the time scale of several minutes to hours. A faster form of desensitization is induced by the auxiliary subunit KCTD12, which interferes with channel activation by binding to the G-protein βγ subunits. Here we show that the two mechanisms of desensitization influence each other. Serine-892 phosphorylation in heterologous cells rearranges KCTD12 at the receptor and slows KCTD12-induced desensitization. Likewise, protein kinase-A activation in hippocampal neurons slows fast desensitization of GABAB receptor-activated K(+) currents while protein kinase-A inhibition accelerates fast desensitization. Protein kinase-A fails to regulate fast desensitization in KCTD12 knock-out mice or knock-in mice with a serine-892 to alanine mutation, thus demonstrating that serine-892 phosphorylation regulates KCTD12-induced desensitization in vivo. Fast current desensitization is accelerated in hippocampal neurons carrying the serine-892 to alanine mutation, showing that tonic serine-892 phosphorylation normally limits KCTD12-induced desensitization. Tonic serine-892 phosphorylation is in turn promoted by assembly of receptors with KCTD12. This cross-regulation of serine-892 phosphorylation and KCTD12 activity sharpens the response during repeated receptor activation.