Biology subjects

Kubouchi, K.

Publications and source records attributed to Kubouchi, K..

2 recordsLinked to original sources

bioRxiv2026

Repeated swim exposure and PKN1a knockout enhance group I mGluR-dependent excitability associated with reduced EAAT3 expression in mouse dentate granule cells

Stress-related experiences alter glutamatergic signaling and neuronal excitability, but the mechanisms that couple experience to dentate granule cell function remain incompletely understood. Here, we examined how protein kinase N1a (PKN1a), a protein kinase C-like serine/threonine kinase, and repeated swim exposure regulate mouse hippocampal dentate granule cell excitability, with a focus on the neuronal glutamate transporter excitatory amino acid transporter 3 (EAAT3) and group I metabotropic glutamate receptors (mGluRs). Five days of repeated swim exposure increased spike firing in mature dentate granule cells from wild-type mice. PKN1a knockout produced a similar increase, and repeated swim did not further enhance firing in knockout mice. The enhanced firing observed after repeated swim exposure and in PKN1a knockout mice was reduced by co-application of an mGluR1 antagonist (LY367385) and an mGluR5 antagonist (MPEP). Inhibition of glutamate transporters with DL-TBOA increased granule cell firing in control wild-type mice but did not further increase firing in repeated-swim wild-type or PKN1a knockout mice, suggesting occlusion of transporter-dependent regulation of excitability. Repeated swim exposure and PKN1a knockout also reduced total and surface expression of EAAT3 in the hippocampus, whereas expression of the glial glutamate transporter EAAT2 was not significantly altered. Finally, PKN1a knockout and repeated swim exposure reduced anxiety-related behavior in the elevated plus maze test. Thus, PKN1a-dependent regulation of EAAT3 may restrain group I mGluR-dependent excitability in dentate granule cells, whereas repeated swim exposure and PKN1a knockout shift this system toward a lower-EAAT3, higher-excitability state accompanied by reduced anxiety-related behavior.

neuroscience↗

bioRxiv2025

ATP-independent phosphate recycling on AGC kinase activation loops induced by alkali metal ions

Changes in extracellular Na and K concentrations have traditionally been considered to influence intracellular signal transduction through alterations in cell volume or membrane potential. However, whether intracellular ion concentration changes directly regulate signaling molecules, independent of these conventional pathways, remains largely unexplored. In this study, we demonstrate that even in the absence of cellular membranes, an increase in Na or K concentration rapidly reduces activation-loop phosphorylation of multiple AGC kinases, including PKN, PKC{zeta}/{lambda}, and p70 S6 kinase. When ion concentrations were reduced, the activation-loop phosphorylation, which had initially decreased, recovered within a short period. Notably, this recovery occurred in the absence of PDK1, a known kinase responsible for the phosphorylation of these activation loops, and did not require ATP or Mg{superscript 2} in lysate assays. 3{superscript 2}P tracing experiments revealed a novel reacquisition of phosphate group mechanism, in which phosphate groups transiently dissociate from the activation loops under high Na or K conditions and are subsequently re-incorporated into the activation loops when ion concentrations are reduced. These findings indicate that elevated Na or K concentrations directly and rapidly reduce the activity of multiple AGC kinases, and that the activity rapidly recovers upon reduction in ion concentrations, through an unconventional phosphate transfer mechanism distinct from canonical protein phosphorylation reactions. Our study suggests the existence of a robust phosphorylation homeostasis mechanism independent of conventional kinase-phosphatase systems, providing new insights into signaling pathways regulated by intracellular Na/K ion dynamics.

biochemistry↗