title: Differential trafficking of carboxyl isoforms of Ca2+-gated (Slo1) potassium channels.
abstract: The pore-forming subunit of the large-conductance Ca(2+)-dependent K(+) (Slo1) channel is encoded by one gene. However, the functional properties of Slo1 channels are diverse in part because of their numerous regulatory mechanisms including posttranslational modification and alternative splicing. In particular, multiple splice variants of the pore-forming subunit have been reported but their significance is only beginning to be elucidated. Here we examined the cell biological properties of the three common C-terminal isoforms that differ in the last 8 (Slo1_ERL and Slo1_VYR) or 61 residues (Slo1_DEC). We found that Slo1_DEC, the longest isoform, shows dramatically reduced surface expression compared to that of Slo1_ERL or Slo1_VYR. Immunocytochemistry revealed that a large fraction of Slo1_DEC remains localized in endoplasmic reticulum (ER). Using a GST fusion protein containing the Slo1_DEC-specific sequence, affinity purification was carried out to isolate interacting proteins. The identified proteins include protein phosphatase 2A (PP2A-A), actin, and tubulin. The PP2A-A interaction is specific to Slo1_DEC and causes a significant reduction of phosphorylation in Slo1_DEC but not Slo1_ERL or Slo1_VYR. The results together support the notion that Slo1_DEC nucleates isoform-specific protein complexes and possesses a cis element(s) for regulating trafficking of the Slo1 channels.
authors.affiliation: Department of Neuroscience and High Throughput Biology Center, Johns Hopkins University School of Medicine, 733 North Broadway, Baltimore, MD 21205, USA.
authors.forename: Donghui
authors.initials: D
authors.lastname: Ma
authors.forename: Takahiro
authors.initials: T
authors.lastname: Nakata
authors.forename: Guangping
authors.initials: G
authors.lastname: Zhang
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hoshi
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Sojin
authors.initials: S
authors.lastname: Shikano
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D006801:Humans; D015640:Ion Channel Gating; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D040901:Proteomics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D020033:Protein Isoforms; D011994:Recombinant Proteins