GABAB receptor phosphorylation regulates KCTD12-induced K⁺ current desensitization.
Bottom Line: Receptor-activated K(+) currents desensitize in the sustained presence of agonist to avoid excessive effects on neuronal activity.GABAB receptor activity reduces protein kinase-A activity, which reduces phosphorylation of serine-892 in GABAB2 and promotes receptor degradation.This cross-regulation of serine-892 phosphorylation and KCTD12 activity sharpens the response during repeated receptor activation.
Affiliation: Department of Biomedicine, University of Basel, 4056 Basel, Switzerland.Show MeSH
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Mentions: PKA inhibition with H89 or PKI accelerates fast desensitization of K+ currents in WT hippocampal neurons. Endogenous PKA activity must therefore provide a high level of basal S892 phosphorylation. Indeed, Western blot analysis of hippocampal neurons revealed that GB2 is highly phosphorylated at S892 (Fig. 5), which is reduced by inhibition of PKA with H89. We next addressed whether phosphorylation of S892 in GB2 is essential for PKA effects on baclofen-induced K+ current desensitization in neurons. We generated S892A knock-in mice carrying a S892 to alanine mutation in the GB2 gene using standard gene targeting techniques (Fig. 6A and B). S892A mice display no overt behavioral abnormalities. Western blot analysis revealed similar levels of GB1a, GB1b and GB2 protein in S892A and WT brain extracts (Fig. 6C). Recordings of baclofen-induced K+ currents from cultured hippocampal neurons revealed that the desensitization was significantly faster in S892A compared to WT neurons (Fig. 6D and E). Activation of PKA with 8-Br-cAMP did not significantly increase τ1 of the desensitization in S892A neurons, in contrast to control WT neurons (Fig. 6E). The τ2 of the desensitization was similar in both genotypes and did not change upon activation of PKA with 8-Br-cAMP (Fig. 6E). The lack of PKA effect in S892A neurons indicates that S892 phosphorylation is mandatory for PKA-mediated attenuation of fast desensitization. In summary, our results show that basal PKA-mediated phosphorylation of S892 slows KCTD12-induced desensitization in neurons.
Affiliation: Department of Biomedicine, University of Basel, 4056 Basel, Switzerland.