title: Cardiac-enriched LIM domain protein fhl2 is required to generate I(Ks) in a heterologous system.
abstract: OBJECTIVE
  Co-expression of the KvLQT1 and minK potassium channel subunits is required to recapitulate I(Ks), the slow component of the cardiac delayed rectifier current, and mutations in either gene cause the congenital Long QT syndrome. It is becoming increasingly well-recognized that multiprotein channel complexes containing proteins capable of modulating channel function assemble at the plasma membrane. Thus, the aim of our study was to identify proteins involved in I(Ks) modulation.
  
  
  RESULTS
  Using a yeast-two-hybrid screen with the intracytoplasmic C-terminus of minK as bait, we identified the cardiac-enriched four-and-a-half LIM domain-containing protein (fhl2) as a potential minK partner. We show interaction between the two proteins in GST pulldown assays and demonstrate overlapping subcellular localization using immunocytochemistry of transfected cells supporting a potential interaction. At the functional level, expression of KvLQT1and minK in HEK cells, which lack endogenous fhl2 protein, generated I(Ks) only when fhl2 was co-expressed. By contrast, in CHO-K1 cells, which express fhl2 endogenously, I(Ks) was suppressed by anti-fhl2 antisense which did not affect the currents generated by KvLQT1alone.
  
  
  CONCLUSIONS
  These data indicate that at least in heterologous cells, the generation of I(Ks) requires fhl2 as an additional protein component.
authors.affiliation: Department of Pharmacology, 561A PRB, Division of Clinical Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232-6602, USA. sabina.kupershmidt@vanderbilt.edu
authors.forename: Sabina
authors.initials: S
authors.lastname: Kupershmidt
authors.forename: Iris C-H
authors.initials: IC
authors.lastname: Yang
authors.forename: Margaret
authors.initials: M
authors.lastname: Sutherland
authors.forename: K Sam
authors.initials: KS
authors.lastname: Wells
authors.forename: Tao
authors.initials: T
authors.lastname: Yang
authors.forename: Ping
authors.initials: P
authors.lastname: Yang
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Balser
authors.forename: Dan M
authors.initials: DM
authors.lastname: Roden
mesh_terms: D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D005818:Genetic Engineering; D018398:Homeodomain Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007150:Immunohistochemistry; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D018398:Homeodomain Proteins; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D016376:Oligonucleotides, Antisense; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D014157:Transcription Factors; C059983:potassium channel protein I(sk)