A splice variant of the two-pore domain potassium channel TREK-1 with only one pore domain reduces the surface expression of full-length TREK-1 channels
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We have identified a novel splice variant of the human and rat two-pore domain potassium (K2P) channel TREK-1. The splice variant TREK-1e results from skipping of exon 5, which causes a frame shift in exon 6. The frame shift produces a novel C-terminal amino acid sequence and a premature termination of translation, which leads to a loss of transmembrane domains M3 and M4 and of the second pore domain. RT-PCR experiments revealed a preferential expression of TREK-1e in kidney, adrenal gland, and amygdala. TREK-1e was nonfunctional when expressed in Xenopus oocytes. However, both the surface expression and the current density of full-length TREK-1 were reduced by co-expression of TREK-1e. Live cell imaging in COS-7 cells transfected with GFP-tagged TREK-1e showed that this splice variant was retained in the endoplasmic reticulum (ER). Attachment of the C-terminus of TREK-1e to two different reporter proteins (Kir2.1 and CD8) led to a strong reduction in the surface expression of these fusion proteins. Progressive truncation of the C-terminus of TREK-1e in these reporter constructs revealed a critical region (amino acids 198 to 205) responsible for the intracellular retention. Mutagenesis experiments indicated that amino acids I204 and W205 are key residues mediating the ER retention of TREK-1e. Our results suggest that the TREK-1e splice variant may interfere with the vesicular traffic of full-length TREK-1 channels from the ER to the plasma membrane. Thus, TREK-1e might modulate the copy number of functional TREK-1 channels at the cell surface, providing a novel mechanism for fine tuning of TREK-1 currents.
KeywordsAlternative splicing K2P channel Potassium channels Splice variant TREK-1
This work was supported by grants of the Deutsche Forschungsgemeinschaft SFB 593, TP A4 to J.D. and 1482-3/2 to N.D., the P.E. Kempkes Foundation (to S.R. and R.P.M.), and the Anneliese Pohl Stiftung to S.R.. We thank Caroline Rolfes and Thorsten Steinfeldt for the isolation of porcine adrenal gland. We are grateful to Andrea Schubert for excellent technical support.
Conflict of interest
The authors declare no conflict of interest.
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