Nuclear localization and dominant-negative suppression by a mutant SKCa3 N-terminal channel fragment identified in a patient with schizophrenia.
The small conductance calcium-activated K+ channel gene SKCa3/KCNN3 maps to 1q21, a region strongly linked to schizophrenia. Recently, a 4-base pair deletion in SKCa3 was reported in a patient with schizophrenia, which truncates the protein at the end of the N-terminal cytoplasmic region (SKCa3Delta). We generated a green fluorescent protein-SKCa3 N-terminal construct (SKCa3-1/285) that is identical to SKCa3Delta except for the last two residues. Using confocal microscopy we demonstrate that SKCa3-1/285 localizes rapidly and exclusively to the nucleus of mammalian cells like several other pathogenic polyglutamine-containing proteins. This nuclear targeting is mediated in part by two polybasic sequences present at the C-terminal end of SKCa3-1/285. In contrast, full-length SKCa3, SKCa2, and IKCa1 polypeptides are all excluded from the nucleus and express as functional channels. When overexpressed in human Jurkat T cells, SKCa3-1/285 can suppress endogenous SKCa2 currents but not voltage-gated K+ currents. This dominant-negative suppression is most likely mediated through the co-assembly of SKCa3-1/285 with native subunits and the formation of non-functional tetramers. The nuclear localization of SKCa3-1/285 may alter neuronal architecture, and its ability to dominantly suppress endogenous small conductance K(Ca) currents may affect patterns of neuronal firing. Together, these two effects may play a part in the pathogenesis of schizophrenia and other neuropsychiatric disorders.
Miller
M J
MJ
Department of Physiology and Biophysics, Division of Human Genetics, University of California Irvine, Irvine, California 92697-4561, USA.
Rauer
H
H
Tomita
H
H
Rauer
H
H
Gargus
J J
JJ
Gutman
G A
GA
Cahalan
M D
MD
Chandy
K G
KG
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004594:Electrophysiology; D017353:Gene Deletion; D005799:Genes, Dominant; D049452:Green Fluorescent Proteins; D006801:Humans; D019169:Jurkat Cells; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry*; D024681:Potassium Channels, Calcium-Activated; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012559:Schizophrenia / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D051640:Small-Conductance Calcium-Activated Potassium Channels; D014162:Transfection
D018076:DNA, Complementary; C406328:KCNN3 protein, human; D008164:Luminescent Proteins; D010455:Peptides; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D011993:Recombinant Fusion Proteins; D051640:Small-Conductance Calcium-Activated Potassium Channels; D049452:Green Fluorescent Proteins