The TRESK (K2P18.1, KCNK18) background potassium channel is expressed in primary sensory
neurons and has been reported to contribute to the regulation of pain sensations.
In the present study, we examined the interaction of TRESK with NDFIP1 (Nedd4 family-interacting
protein 1) in the Xenopus oocyte expression system by two-electrode voltage clamp
and biochemical methods. We showed that the coexpression of NDFIP1 abolished the TRESK
current under the condition where the other K+ channels were not affected. Mutations
in the three PPxY motifs of NDFIP1, which are responsible for the interaction with
the Nedd4 ubiquitin ligase, prevented a reduction in the TRESK current. Furthermore,
the overexpression of a dominant-negative Nedd4 construct in the oocytes coexpressing
TRESK with NDFIP1 partially reversed the down-modulating effect of the adaptor protein
on the K+ current. The biochemical data were also consistent with the functional results.
An interaction between epitope-tagged versions of TRESK and NDFIP1 was verified by
co-immunoprecipitation experiments. The coexpression of NDFIP1 with TRESK induced
the ubiquitination of the channel protein. Altogether, the results suggest that TRESK
is directly controlled by and highly sensitive to the activation of the NDFIP1-Nedd4
system. The NDFIP1-mediated reduction in the TRESK component may induce depolarization,
increase excitability, and attenuate the calcium dependence of the membrane potential
by reducing the calcineurin-activated fraction in the ensemble background K+ current.
