Interaction with 14‐3‐3 proteins promotes functional expression of the potassium channels TASK‐1 and TASK‐3

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Abstract
The two‐pore‐domain potassium channels TASK‐1, TASK‐3 and TASK‐5 possess a conserved C‐terminal motif of five amino acids. Truncation of the C‐terminus of TASK‐1 strongly reduced the currents measured after heterologous expression in Xenopus oocytes or HEK293 cells and decreased surface membrane expression of GFP‐tagged channel proteins. Two‐hybrid analysis showed that the C‐terminal domain of TASK‐1, TASK‐3 and TASK‐5, but not TASK‐4, interacts with isoforms of the adapter protein 14‐3‐3. A pentapeptide motif at the extreme C‐terminus of TASK‐1, RRx(S/T)x, was found to be sufficient for weak but significant interaction with 14‐3‐3, whereas the last 40 amino acids of TASK‐1 were required for strong binding. Deletion of a single amino acid at the C‐terminal end of TASK‐1 or TASK‐3 abolished binding of 14‐3‐3 and strongly reduced the macroscopic currents observed in Xenopus oocytes. TASK‐1 mutants that failed to interact with 14‐3‐3 isoforms (V411*, S410A, S410D) also produced only very weak macroscopic currents. In contrast, the mutant TASK‐1 S409A, which interacts with 14‐3‐3‐like wild‐type channels, displayed normal macroscopic currents. Co‐injection of 14‐3‐3ζ cRNA increased TASK‐1 current in Xenopus oocytes by about 70 %. After co‐transfection in HEK293 cells, TASK‐1 and 14‐3‐3ζ (but not TASK‐1ΔC5 and 14‐3‐3ζ) could be co‐immunoprecipitated. Furthermore, TASK‐1 and 14‐3‐3 could be co‐immunoprecipitated in synaptic membrane extracts and postsynaptic density membranes. Our findings suggest that interaction of 14‐3‐3 with TASK‐1 or TASK‐3 may promote the trafficking of the channels to the surface membrane.