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J. Biol. Chem., Vol. 276, Issue 30, 27753-27756, July 27, 2001

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ACCELERATED PUBLICATION
Nuclear Localization and Dominant-negative Suppression by a Mutant SKCa3 N-terminal Channel Fragment Identified in a Patient with Schizophrenia^*

Mark J. Miller, Heiko Rauer^§, Hiroaki Tomita, Heike Rauer^¶, J. Jay Gargus, George A. Gutman^**, Michael D. Cahalan, and K. George Chandy

From the  Department of Physiology and Biophysics,  Division of Human Genetics, Department of Pediatrics, and ^** Department of Microbiology and Molecular Genetics, University of California Irvine, Irvine, California 92697-4561

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 (SKCa3). We generated a green fluorescent protein-SKCa3 N-terminal construct (SKCa3-1/285) that is identical to SKCa3 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.

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