title: PIKfyve sensitivity of hERG channels.
abstract: OBJECTIVE
  Human ether-a-go-go (hERG) channels contribute to cardiac repolarization and participate in the regulation of tumor cell proliferation. Mutations in hERG channels may cause long QT syndrome and sudden cardiac death due to ventricular arrhythmias. HERG channel activity is up-regulated by the serum- and glucocorticoid-inducible kinase isoforms SGK1 and SGK3. Related kinases are protein kinase B (PKB/Akt) isoforms. SGK´s and PKB/Akt´s activate phosphatidylinositol-3-phosphate-5-kinase PIKfyve, which in turn up-regulates several carriers and channels. An effect of PIKfyve on hERG channels, has, however, never been shown. The present study thus explored the putative influence of PIKfyve on hERG channel expression and activity.
  
  
  METHODS
  hERG channels were expressed in Xenopus oocytes with or without PIKfyve and/or PKB, expression of endogenous and injected hERG quantified by RT-PCR, and hERG channel activity determined utilizing dual electrode voltage clamp. Moreover, hERG protein abundance in the cell membrane was visualized utilizing specific antibody binding and subsequent confocal microscopy and quantified by chemiluminescence.
  
  
  RESULTS
  Coexpression of wild type PIKfyve increased hERG channel activity in hERG-expressing Xenopus oocytes. hERG channel activity was further increased by coexpression of PKB, an effect augmented by additional coexpression of PIKfyve, but not by additional coexpression of PKB/Akt-resistant PIKfyve mutant PIKfyve(S318A). Coexpression of PIKfyve increased hERG channel protein abundance in the cell membrane. Inhibition of hERG channel insertion into the cell membrane by Brefeldin A (5 µM) resulted in a decline of current, which was similar in Xenopus oocytes expressing hERG together with PIKfyve and in Xenopus oocytes expressing hERG alone.
  
  
  CONCLUSIONS
  hERG is up-regulated by PIKfyve, which is in turn activated by PKB/Akt.
authors.affiliation: Department of Physiology, University of Tübingen, Gmelinstrasse 5, Tübingen, Germany.
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Pakladok
authors.forename: Ahmad
authors.initials: A
authors.lastname: Almilaji
authors.forename: Carlos
authors.initials: C
authors.lastname: Munoz
authors.forename: Ioana
authors.initials: I
authors.lastname: Alesutan
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000818:Animals; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D014981:Xenopus / Q000254:growth & development / Q000502:physiology; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D051638:Ether-A-Go-Go Potassium Channels; D017874:Immediate-Early Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D000099184:Serum-Glucocorticoid Regulated Kinases