Development of a medium throughput whole-cell microtiter plate Thr286 autophosphorylation assay for CaMKIIα using ELISA.

Ca2+/calmodulin-dependent protein kinase II alpha (CaMKIIα) is a multifunctional Ser/Thr kinase involved in several neuronal signaling pathways including synaptic plasticity. CaMKIIα autonomous activity is highly dependent on Thr286 autophosphorylation (pThr286), which is widely used as a readout for its enzymatic activity. To readily characterise compounds and potential drug candidates targeting CaMKIIα, a simple, generic cell-based assay for quantification of pThr286 levels is needed. In this study, we present a cell-based assay using an adapted ELISA as a suitable and higher throughput alternative to Western blotting. In this 96-well plate-based assay, we use whole HEK293T cells recombinantly expressing CaMKIIα and apply a phospho-specific antibody to detect pThr286 levels by chemiluminescence. In parallel, total CaMKIIα expression levels are detected by fluorescence using an Alexa488-conjugated anti-myc antibody targeting a C-terminal myc-tag. By multiplexing chemiluminescence and fluorescence, phosphorylation levels are normalised to CaMKIIα total expression within each well. The specificity of the assay was confirmed using a phosphodead mutant (T286A) of CaMKIIα. By applying Ca2+ or known CaMKIIα inhibitors (KN93, tatCN21 and AS100105) and obtaining concentration-response curves, we demonstrate high sensitivity and validity of the assay. Lastly, we demonstrate the versatility of the assay by determining autophosphorylation levels in CaMKIIα patient-related mutations, known to possess altered pThr286 responses (E109D, E183V and H282R). The established assay for CaMKIIα is a reproducible, easily implemented, and facile ELISA-based assay that allows for reliable quantification of pThr286 levels.

GHB analogs confer neuroprotection through specific interaction with the CaMKIIα hub domain.

Ca2+/calmodulin-dependent protein kinase II alpha subunit (CaMKIIα) is a key neuronal signaling protein and an emerging drug target. The central hub domain regulates the activity of CaMKIIα by organizing the holoenzyme complex into functional oligomers, yet pharmacological modulation of the hub domain has never been demonstrated. Here, using a combination of photoaffinity labeling and chemical proteomics, we show that compounds related to the natural substance γ-hydroxybutyrate (GHB) bind selectively to CaMKIIα. By means of a 2.2-Å x-ray crystal structure of ligand-bound CaMKIIα hub, we reveal the molecular details of the binding site deep within the hub. Furthermore, we show that binding of GHB and related analogs to this site promotes concentration-dependent increases in hub thermal stability believed to alter holoenzyme functionality. Selectively under states of pathological CaMKIIα activation, hub ligands provide a significant and sustained neuroprotection, which is both time and dose dependent. This is demonstrated in neurons exposed to excitotoxicity and in a mouse model of cerebral ischemia with the selective GHB analog, HOCPCA (3-hydroxycyclopent-1-enecarboxylic acid). Together, our results indicate a hitherto unknown mechanism for neuroprotection by a highly specific and unforeseen interaction between the CaMKIIα hub domain and small molecule brain-penetrant GHB analogs. This establishes GHB analogs as powerful tools for investigating CaMKII neuropharmacology in general and as potential therapeutic compounds for cerebral ischemia in particular.