title: The phosphorylation state of GluR1 subunits determines the susceptibility of AMPA receptors to calpain cleavage.
abstract: The alpha-Amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid receptor (AMPAR) is an ionotropic glutamate receptor that governs most of excitatory synaptic transmission in neurons. In vitro biochemical assay has shown that calpain, a Ca2+-activated protease, can cleave AMPAR GluR1 subunits. Our physiological study found that calpain, which was activated by prolonged stimulation of the N-methyl-D-aspartate receptor (100 microM, 10 min), caused a substantial suppression of AMPAR currents in cortical neurons. Since the phosphorylation sites of GluR1 by several protein kinases are located in close proximity to the calpain cleavage sites, we investigated the effect of phosphorylation on the susceptibility of GluR1 to calpain cleavage. Interestingly, we found that the calpain regulation of AMPAR currents was diminished by inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII) but was augmented by inhibition of protein phosphatase 1/2A (PP1/2A). In agreement with this, in vitro assay showed that the calpain-induced proteolytic cleavage of GluR1 C-terminal fusion protein was strongly potentiated by adding the purified active CaMKII, and GluR1 phosphorylated at Ser831 by CaMKII is much more sensitive to calpain cleavage. Taken together, our data suggest that calpain activation suppresses AMPA receptor currents via proteolytic cleavage of GluR1 subunits, and the susceptibility of AMPARs to calpain cleavage is determined by the phosphorylation state of GluR1 subunits, which is mediated by CaMKII-PP1/2A activity.
authors.affiliation: Department of Physiology and Biophysics, State University of New York at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York 14214, USA.
authors.forename: Eunice Y
authors.initials: EY
authors.lastname: Yuen
authors.forename: Wenhua
authors.initials: W
authors.lastname: Liu
authors.forename: Zhen
authors.initials: Z
authors.lastname: Yan
mesh_terms: D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000201:enzymology*; D004789:Enzyme Activation / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000378:metabolism*; D013997:Time Factors
chemical_list: D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002154:Calpain; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D021122:Protein Subunits; D018091:Receptors, AMPA