Auto-inhibition of Ca(2+)/calmodulin-dependent protein kinase II by its ATP-binding domain

Disruption of auto-inhibition underlies conformational signaling of ASIC1a to induce neuronal necroptosis

We reported previously that acid-sensing ion channel 1a (ASIC1a) mediates acidic neuronal necroptosis via recruiting receptor-interacting protein kinase 1 (RIPK1) to its C terminus (CT), independent of its ion-conducting function. Here we show that the N-terminus (NT) of ASIC1a interacts with its CT to form an auto-inhibition that prevents RIPK1 recruitment/activation under resting conditions. The interaction involves glutamate residues at distal NT and is disrupted by acidosis. Expression of mutant ASIC1a bearing truncation or glutamate-to-alanine substitutions at distal NT causes constitutive cell death. The NT-CT interaction is further disrupted by N-ethylmaleimide-sensitive fusion ATPase (NSF), which associates with ASIC1a-NT under acidosis, facilitating RIPK1 interaction with ASIC1a-CT. Importantly, a membrane-penetrating synthetic peptide representing the distal 20 ASIC1a NT residues, NT_1–20, reduced neuronal damage in both in vitro model of acidotoxicity and in vivo mouse model of ischemic stroke, demonstrating the therapeutic potential of targeting the auto-inhibition of ASIC1a for neuroprotection against acidotoxicity.

Acid-sensing ion channel 1a (ASIC1a) mediates acidic neuronal necroptosis via recruiting receptor-interacting protein kinase 1 (RIPK1). Here authors show that auto-inhibition of ASICa prevents RIPK1 recruitment and demonstrate that targeting the auto-inhibition has therapeutic potential to prevent acidotoxicity.

Phosphorylation of CaMKII in the rat dorsal raphe nucleus plays an important role in sleep-wake regulation

The Ca(2+) modulation in the dorsal raphe nucleus (DRN) plays an important role in sleep-wake regulation. Calmodulin-dependent kinase II (CaMKII) is an important signal-transducing molecule that is activated by Ca(2+) . This study investigated the effects of intracellular Ca(2+) /CaMKII signaling in the DRN on sleep-wake states in rats. Maximum and minimum CaMKII phosphorylation was detected at Zeitgeber time 21 (ZT 21; wakefulness state) and ZT 3 (sleep state), respectively, across the light-dark rhythm in the DRN in rats. Six-hour sleep deprivation significantly reduced CaMKII phosphorylation in the DRN. Microinjection of the CAMKII activation inhibitor KN-93 (5 or 10 nmol) into the DRN suppressed wakefulness and enhanced rapid-eye-movement sleep (REMS) and non-REM sleep (NREMS). Application of a high dose of KN-93 (10 nmol) increased slow-wave sleep (SWS) time, SWS bouts, the mean duration of SWS, the percentage of SWS relative to total sleep, and delta power density during NREMS. Microinjection of CaCl2 (50 nmol) in the DRN increased CaMKII phosphorylation and decreased NREMS, SWS, and REMS. KN-93 abolished the inhibitory effects of CaCl2 on NREMS, SWS, and REMS. These data indicate a novel wake-promoting and sleep-suppressing role for the Ca(2+) /CaMKII signaling pathway in DRN neurons. We propose that the intracellular Ca(2+) /CaMKII signaling in the dorsal raphe nucleus (DRN) plays wake-promoting and sleep-suppressing role in rats. Intra-DRN application of KN-93 (CaMKII activation inhibitor) suppressed wakefulness and enhanced rapid-eye-movement sleep (REMS) and non-REMS (NREMS). Intra-DRN application of CaCl2 attenuated REMS and NREMS. We think these findings should provide a novel cellular and molecular mechanism of sleep-wake regulation.

Switching reversibility to irreversibility in glycogen synthase kinase 3 inhibitors: clues for specific design of new compounds

Development of kinase-targeted therapies for central nervous system (CNS) diseases is a great challenge. Glycogen synthase kinase 3 (GSK-3) offers a great potential for severe CNS unmet diseases, being one of the inhibitors on clinical trials for different tauopathies. Following our hypothesis based on the enhanced reactivity of residue Cys199 in the binding site of GSK-3, we examine here the suitability of phenylhalomethylketones as irreversible inhibitors. Our data confirm that the halomethylketone unit is essential for the inhibitory activity. Moreover, addition of the halomethylketone moiety to reversible inhibitors turned them into irreversible inhibitors with IC(50) values in the nanomolar range. Overall, the results point out that these compounds might be useful pharmacological tools to explore physiological and pathological processes related to signaling pathways regulated by GSK-3 opening new avenues for the discovery of novel GSK-3 inhibitors.

Regulation and function of Ca2+-calmodulin-dependent protein kinase II of fast-twitch rat skeletal muscle

The activation and function of Ca(2+)-calmodulin-dependent kinase II (CaMKII) in contracting rat skeletal muscle was examined. The increase in autonomous activity and phosphorylation at Thr(287) of CaMKII of gastrocnemius muscle in response to contractions in situ was rapid and transient, peaking at 1-3 min, but reversed after 30 min of contractions. There was a positive correlation between CaMKII phosphorylation at Thr(287) and autonomous CaMKII activity. In contrast to the rapid and transient increase in autonomous CaMKII activity, the phosphorylation of the putative CaMKII substrate trisk95/triadin was rapid and sustained during contractions. There were no changes in CaMKII activity and phosphorylation or trisk95 phosphorylation in the resting contralateral muscles during stimulation. When fast-twitch muscles were contracted ex vivo, CaMKII inhibition resulted in a greater magnitude of fatigue as well as blunted CaMKII and trisk95 phosphorylation, identifying trisk95 as a physiological CaMKII substrate. In summary, skeletal muscle CaMKII activation was rapid and sustained during exercise/contraction and is mediated by factors within the contracting muscle, probably through allosteric activation via Ca(2+)-CaM. CaMKII may signal through trisk95 to modulate Ca(2+) release in fast-twitch rat skeletal muscle during exercise/contraction.

An endogenous inhibitor of calcium/calmodulin-dependent kinase II is up-regulated during consolidation of fear memory

CaMKIINalpha and CaMKIINbeta are endogenous inhibitors of the abundant synaptic protein, calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII exerts a prominent function in memory formation and the endogenous inhibitors might be important regulators of CaMKII activity during this process. Here we investigated whether or not CaMKIINalpha and CaMKIINbeta gene expressions are regulated in the mouse hippocampus and amygdala after background contextual fear conditioning. Quantitative real-time PCR revealed that the hippocampal expression of CaMKIINalpha mRNA was up-regulated 30 and 60 min after conditioning. In contrast, CaMKIINbeta mRNA expression did not change. The up-regulation of CaMKIINalpha expression was specific for the fear memory because the context alone and a shock control did not induce any variation of transcription level. Quantification of in situ hybridization signals showed that CaMKIINalpha expression increased in hippocampal area CA1, in the dentate gyrus (DG) and in the lateral amygdala (LA) 30 min after training. Our findings show an up-regulation in the expression of the endogenous inhibitor gene CaMKIINalpha during consolidation of fear memory. The early onset and the amplitude of the up-regulation are similar to those of immediate-early genes. Taken together, our results suggest that the CaMKIINalpha inhibitor has a physiological role in controlling CaMKII activity from an early stage of memory consolidation.

SAR and 3D-QSAR studies on thiadiazolidinone derivatives: exploration of structural requirements for glycogen synthase kinase 3 inhibitors

The 2,4-disubstituted thiadiazolidinones (TDZD) are described as the first ATP-noncompetitive GSK-3 inhibitors. Following an SAR study about TDZD, different structural modifications in the heterocyclic ring aimed to test the influence of each heteroatom on the biological study are here reported here. Various compounds such as hydantoins, dithiazolidindiones, rhodanines, maleimides, and triazoles were synthesized and screened as GSK-3 inhibitors. After an extensive SAR study among these different heterocyclic families, TDZDs have been revealed as a privileged scaffold for the selective inhibition of GSK-3. A CoMFA analysis was also performed highlighting the molecular electrostatic field interaction in the interaction of TDZDs with GSK-3. Moreover, first mapping studies indicate two binding modes which in turn might imply relevant differences in the mechanism that underly the inhibitory activity of TDZDs.

Mechanism of the T286A-mutant alphaCaMKII interactions with Ca2+/calmodulin and ATP

The role of adenosine 5'-triphosphate (ATP) in the activation mechanism of alpha-Ca(2+)/calmodulin-dependent protein kinase II (alphaCaMKII) was investigated using the T286A non-autophosphorylatable mutant of alphaCaMKII. Characterization of the T286A-alphaCaMKII mutant revealed k(cat) = 0.06 +/- 0.02 s(-1) for the T286A mutant, a 6 (+/- 2)-fold lower value compared to wild-type alphaCaMKII with 100 microM smooth muscle myosin light chain (MLC) as substrate. MLC phosphorylation by the T286A mutant and wild-type alphaCaMKII was cooperative, with Hill coefficients 2.3 +/- 0.1 and 2.4 +/- 0.3, respectively. K(m) values for MLC were 96 +/- 28 microM with T286A-alphaCaMKII and 49 +/- 29 microM for wild-type alphaCaMKII. Thus, while the activity of alphaCaMKII was sensitive to mutation of the Thr(286) residue to Ala, the mechanisms of the wild-type and T286A mutant enzyme appeared similar. K(d) for Ca(2+)/calmodulin was 2-fold reduced to 40 nM compared to that of wild-type alphaCaMKII (75 nM). ATP induced a 9-fold stabilization of Ca(2+)/calmodulin binding to the T286A mutant enzyme. Fluorescence stopped-flow kinetic experiments revealed that two Ca(2+)/calmodulin-enzyme complexes were formed, the first, unaffected by ATP, with association and dissociation rate constants of 2 x 10(7) M(-1) s(-1) and 5 s(-1), respectively, containing calmodulin in extended conformation. The second complex, in which calmodulin adopted a compact conformation, was formed with association rate constant 3 x 10(6) M(-1) s(-1) and dissociation at 0.15 s(-1) in the absence and 0.015 s(-1) in the presence of ATP. These data show that ATP is involved in the activation mechanism by forming two classes of Ca(2+)/calmodulin.alphaCaMKII.ATP complex. It is likely that only one of the complexes is on the activation pathway.

Differential functional properties of calmodulin-dependent protein kinase IIgamma variants isolated from smooth muscle

Six variants of calmodulin-dependent protein kinase IIgamma were isolated from a ferret-aorta smooth-muscle cDNA library. Variant G-2 is generated by a novel alternative polyadenylation, utilizing a site contained in an intron. The last 77 residues of the association domain are replaced with 99 residues of a unique sequence containing Src homology 3-domain-binding motifs, which alter catalytic activity. Variant C-2 has an eight-residue deletion in an ATP-binding motif and does not autophosphorylate Thr(286), but does phosphorylate exogenous substrate. Two variants, B and J, autodephosphorylate. Four variants differing only in the variable domain have differing catalytic activities, despite identical sequences in the catalytic domains. Thus structural features determined by variable and association domains are important for the catalytic activity of calmodulin-dependent protein kinase II.

Structure-function of the multifunctional Ca2+/calmodulin-dependent protein kinase II

Ca2+/calmodulin (CaM)-dependent protein kinase (CaMKII) is a ubiquitous mediator of Ca2+-linked signalling that phosphorylates a wide range of substrates to co-ordinate and regulate Ca2+-mediated alterations in cellular function. The transmission of information by the kinase from extracellular stimuli and the intracellular Ca2+ rise is not passive. Rather, its multimeric structure and autoregulation enable this enzyme to participate actively in the sensitivity, timing and location of its action. CaMKII can: (i) be activated in a Ca2+-spike frequency-dependent manner; (ii) become independent of its initial Ca2+/CaM activators; and (iii) undergo a 'molecular switch-like' behaviour, which is crucial for certain forms of learning and memory. CaMKII is derived from a family of four homologous but distinct genes, with over 30 alternatively spliced isoforms described at present. These isoforms possess diverse developmental and anatomical expression patterns, as well as subcellular localization. Six independent catalytic/autoregulatory domains are connected by a narrow stalk-like appendage to each hexameric ring within the dodecameric structure. Ca2+/CaM binding activates the enzyme by disinhibiting the autoregulatory domain; this process initiates an intra-holoenzyme autophosphorylation reaction that induces complex changes in the enzyme's sensitivity to Ca2+/CaM, including the generation of Ca2+/CaM-independent (autonomous) activity and marked increase in affinity for CaM. The role of CaMKII in Ca2+ signal transduction is shaped by its autoregulation, isoenzymic type and subcellular localization. The molecular determinants and mechanisms producing these processes are discussed as they relate to the structure-function of this multifunctional protein kinase.