Phosphorylation of the GluN2B C-tail at S1303 by CaMKII or DAPK1: no indication for involvement in neuronal mechanisms related to ischemia or LTP
Binding of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) and the death associated protein kinase 1 (DAPK1) to the NMDA-type glutamate receptor (NMDAR) subunit GluN2B near S1303 have been implicated in excitoxic/ischemic neuronal cell death. The GluN2BΔCaMKII mutation (L1298A, R1300Q) is neuroprotective, but abolishes only CaMKII but not DAPK1 binding. However, both kinases can additionally phosphorylate GluN2B S1303. Thus, we here set out test the possible contribution of the S1303 phosphorylation to neuronal cell death. We found that the GluN2BΔCaMKII mutation completely abolished the strong S1303 phosphorylation by CaMKII and reduced a modest phosphorylation by DAPK1, suggesting that the neuroprotective effect of the mutation could be disrupted phosphorylation. However, S1303 phosphorylation was not increased by excitotoxic insults in hippocampal slices or by global cerebral ischemia induced by cardiac arrest and cardiopulmonary resuscitation in vivo. In hippocampal cultures, S1303 phosphorylation was induced by chemical LTD but not LTP stimuli. Thus, even though GluN2BΔCaMKII mutation abolishes both binding of and phosphorylation by CaMKII, these results indicate that the additional effect on phosphorylation needs to be considered only in LTD but not in LTP or ischemia/excitotoxicity.