Dissociation of protein kinase-mediated regulation of metabotropic glutamate receptor 7 (mGluR7) interactions with calmodulin and regulation of mGluR7 function.

Sorensen SD, Macek TA, Cai Z, Saugstad JA, Conn PJ
Mol Pharmacol. 2002 61 (6): 1303-12

PMID: 12021391 · DOI:10.1124/mol.61.6.1303

Presynaptic metabotropic glutamate receptors (mGluRs) often act as feedback inhibitors of synaptic transmission and serve important roles in defining the activity of glutamatergic synapses. Recent investigations have begun to identify novel interactions of presynaptic mGluRs, especially mGluR7, with multiple protein kinases and putative regulatory proteins that probably serve to further shape the overall activity of glutamatergic synapses. In the present study, we report that in addition to protein kinase C (PKC), cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) can inhibit calmodulin (CaM) interactions with the carboxyl-terminal tail of mGluR7. These actions are mediated by PKC-, PKA-, or PKG-dependent phosphorylation of mGluR7 at a single serine residue, Ser(862), in the carboxyl terminus of the receptor. Mutation of this residue inhibits kinase-mediated phosphorylation of the mGluR7 carboxyl terminus and reverses kinase-mediated inhibition of CaM binding to mGluR7. However, PKC-mediated inhibition of the functional coupling of mGluR7 to G protein-coupled inward rectifier potassium (GIRK) currents in a heterologous expression system is not affected by mutating Ser(862). Furthermore, mutation of Ser(862) to glutamate to mimic receptor phosphorylation and inhibit CaM interactions with mGluR7 does not affect receptor function. These studies demonstrate that the ability of these second messenger-dependent kinases to inhibit mGluR7-mediated activation of GIRK current is not dependent on the phosphorylation of Ser(862) or the regulation of CaM binding to mGluR7. Furthermore, our studies suggest that CaM binding is not required for mGluR7-mediated activation of GIRK current.

MeSH Terms (19)

Amino Acid Substitution Animals Calmodulin Cells, Cultured Cyclic AMP-Dependent Protein Kinases Cyclic GMP-Dependent Protein Kinases G Protein-Coupled Inwardly-Rectifying Potassium Channels Humans Phosphorylation Point Mutation Potassium Channel Blockers Potassium Channels Potassium Channels, Inwardly Rectifying Protein Kinase C Rats Receptors, Metabotropic Glutamate Second Messenger Systems Serine Transfection

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