Protein Kinase C Modulates Inactivation of Kv3.3 Channels
ABSTRACT Modulation of some Kv3 family potassium channels by protein kinase C (PKC) regulates their amplitude and kinetics and adjusts firing patterns of auditory neurons in response to stimulation. Nevertheless, little is known about the modulation of Kv3.3, a channel that is widely expressed throughout the nervous system and is the dominant Kv3 family member in auditory brainstem. We have cloned the cDNA for the Kv3.3 channel from mouse brain and have expressed it in a mammalian cell line and in Xenopus oocytes to characterize its biophysical properties and modulation by PKC. Kv3.3 currents activate at positive voltages and undergo inactivation with time constants of 150-250 ms. Activators of PKC increased current amplitude and removed inactivation of Kv3.3 currents, and a specific PKC pseudosubstrate inhibitor peptide prevented the effects of the activators. Elimination of the first 78 amino acids of the N terminus of Kv3.3 produced noninactivating currents suggesting that PKC modulates N-type inactivation, potentially by phosphorylation of sites in this region. To identify potential phosphorylation sites, we investigated the response of channels in which serines in this N-terminal domain were subjected to mutagenesis. Our results suggest that serines at positions 3 and 9 are potential PKC phosphorylation sites. Computer simulations of model neurons suggest that phosphorylation of Kv3.3 by PKC may allow neurons to maintain action potential height during stimulation at high frequencies, and may therefore contribute to stimulus-induced changes in the intrinsic excitability of neurons such as those of the auditory brainstem.
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ABSTRACT: Mutations in Kv3.3 cause spinocerebellar ataxia type 13 (SCA13). Depending on the causative mutation, SCA13 is either a neurodevelopmental disorder that is evident in infancy or a progressive neurodegenerative disease that emerges during adulthood. Previous studies did not clarify the relationship between these distinct clinical phenotypes and the effects of SCA13 mutations on Kv3.3 function. The F448L mutation alters channel gating and causes early-onset SCA13. R420H and R423H suppress Kv3 current amplitude by a dominant negative mechanism. However, R420H results in the adult form of the disease whereas R423H produces the early-onset, neurodevelopmental form with significant clinical overlap with F448L. Since individuals with SCA13 have one wild type and one mutant allele of the Kv3.3 gene, we analysed the properties of tetrameric channels formed by mixtures of wild type and mutant subunits. We report that one R420H subunit and at least one R423H subunit can co-assemble with the wild type protein to form active channels. The functional properties of channels containing R420H and wild type subunits strongly resemble those of wild type alone. In contrast, channels containing R423H and wild type subunits show significantly altered gating, including a hyperpolarized shift in the voltage dependence of activation, slower activation, and modestly slower deactivation. Notably, these effects resemble the modified gating seen in channels containing a mixture of F448L and wild type subunits, although the F448L subunit slows deactivation more dramatically than the R423H subunit. Our results suggest that the clinical severity of R423H reflects its dual dominant negative and dominant gain of function effects. However, as shown by R420H, reducing current amplitude without altering gating does not result in infant onset disease. Therefore, our data strongly suggest that changes in Kv3.3 gating contribute significantly to an early age of onset in SCA13.The Journal of Physiology 01/2012; 590(Pt 7):1599-614. DOI:10.1113/jphysiol.2012.228205 · 4.54 Impact Factor
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ABSTRACT: We recently identified KCNC3, encoding the Kv3.3 voltage-gated potassium channel, as the gene mutated in SCA13. One g.10684G>A (p.Arg420His) mutation caused late-onset ataxia resulting in a nonfunctional channel subunit with dominant-negative properties. A French early-onset pedigree with mild mental retardation segregated a g.10767T>C (p.Phe448Leu) mutation. This mutation changed the relative stability of the channel's open conformation. Coding exons were amplified and sequenced in 260 autosomal-dominant ataxia index cases of European descent. Functional analyses were performed using expression in Xenopus oocytes. The previously identified p.Arg420His mutation occurred in three families with late-onset ataxia. A novel mutation g.10693G>A (p.Arg423His) was identified in two families with early-onset. In one pedigree, a novel g.10522G>A (p.Arg366His) sequence variant was seen in one index case but did not segregate with affected status in the respective family. In a heterologous expression system, the p.Arg423His mutation exhibited dominant-negative properties. The p.Arg420His mutation, which results in a nonfunctional channel subunit, was recurrent and associated with late-onset progressive ataxia. In two families the p.Arg423His mutation was associated with early-onset slow-progressive ataxia. Despite a phenotype reminiscent of the p.Phe448Leu mutation, segregating in a large early-onset French pedigree, the p.Arg423His mutation resulted in a nonfunctional subunit with a strong dominant-negative effect.Human Mutation 02/2010; 31(2):191-6. DOI:10.1002/humu.21165 · 5.05 Impact Factor
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ABSTRACT: Protein kinase C (PKC) plays critical roles in neuronal activity and is widely expressed in striatal neurons. However, it is not clear how PKC activation regulates the excitability of striatal cholinergic interneurons. In the present study, we found that PKC activation significantly inhibited A-type potassium current (I(A)), but had no effect on delayed rectifier potassium currents. Consistently, application of PKC activator caused an increase of firing in response to depolarizing currents in cholinergic interneurons, which was persistent in the presence of both excitatory and inhibitory neurotransmission blockers. These excitatory effects of PKC could be partially mimicked and occluded by blockade of I(A) with potassium channel blocker 4-aminopyridine. In addition, immunostaining demonstrated that PKCalpha, but not PKCgamma and PKCepsilon, was expressed in cholinergic interneurons. Furthermore, activation of group I metabotropic glutamate receptors (mGluRs) led to an inhibition of I(A) through a PKC-dependent pathway. These data indicate that activation of PKC, most likely PKCalpha, increases the neuronal excitability of striatal cholinergic interneurons by down-regulating I(A). Group I mGluR-mediated I(A) inhibition might be important for the glutamatergic regulation of cholinergic tone in the neostriatum.Journal of Neurophysiology 09/2009; 102(4):2453-61. DOI:10.1152/jn.00325.2009 · 3.04 Impact Factor