TRESK (K2P18.1) Background Potassium Channel Is Activated by Novel-Type Protein Kinase C via Dephosphorylation

TRESK (K2P18.1) background K⁺ channel is a major determinant of the excitability of primary sensory neurons. It has been reported that human TRESK is activated by the protein kinase C (PKC) activator PMA (phorbol 12-myristate 13-acetate) in Xenopus oocytes. In the present study, we investigated the mechanism of this PKC-dependent TRESK regulation. We show that TRESK is activated by coexpression of the novel-type PKC isoforms η and ε The effect of PKC is not mediated by calcineurin phosphatase, which is known to evoke the calcium-dependent TRESK activation. Mutations of the calcineurin-binding sites in the channel (PQAAAS-AQAP) did not influence the PMA-induced increase of potassium current. In sharp contrast, the mutations of the target residue of calcineurin in TRESK, S264A, and S264E prevented the effect of PMA. The enforced phosphorylation of S264 by coexpression of a microtubule-affinity regulating kinase construct (MARK2Δ) also abolished the PKC-dependent TRESK activation. These results suggest that, in addition to calcineurin, PKC regulates TRESK by changing the phosphorylation status of S264. Coexpression of PKC slowed recovery of the K⁺ current to the resting state after the calcineurin-dependent dephosphorylation of TRESK. Therefore, the likely mechanism of action is the PKC-dependent inhibition of the kinase responsible for the (re)phosphorylation of the channel at S264. The PKC-dependent dephosphorylation of TRESK protein was also detected by the Phos-tag SDS-PAGE method. In summary, the activation of novel-type PKC results in the slow (indirect) dephosphorylation of TRESK at the regulatory residue S264 in a calcineurin-independent manner.