Article

KCa1.1 Potassium Channels Regulate Key Proinflammatory and Invasive Properties of Fibroblast-like Synoviocytes in Rheumatoid Arthritis

Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 11/2011; 287(6):4014-22. DOI: 10.1074/jbc.M111.312264
Source: PubMed

ABSTRACT

Fibroblast-like synoviocytes (FLS) play important roles in the pathogenesis of rheumatoid arthritis (RA). Potassium channels
have regulatory roles in many cell functions. We have identified the calcium- and voltage-gated KCa1.1 channel (BK, Maxi-K,
Slo1, KCNMA1) as the major potassium channel expressed at the plasma membrane of FLS isolated from patients with RA (RA-FLS). We further
show that blocking this channel perturbs the calcium homeostasis of the cells and inhibits the proliferation, production of
VEGF, IL-8, and pro-MMP-2, and migration and invasion of RA-FLS. Our findings indicate a regulatory role of KCa1.1 channels
in RA-FLS function and suggest this channel as a potential target for the treatment of RA.

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Available from: Liang Sun, Jul 19, 2014
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    • "Together with work from Hu and coworkers (Hu et al., 2012), these findings strongly suggest that two types of calcium-activated potassium channels, KCa3.1 and KCa1.1 may represent interesting new therapeutic targets in RA. Although these channels show similar functions, they may have qualitatively different effects on RA-SFs, as indicated by differential effects of KCa1.1 and KCa3.1 blockade on IL-6 expression/secretion (Hu et al., 2012). Ultimately, the relative contribution of each channel to the pathogenetic process will require in vivo data from knockout mouse strains and other suitable approaches. "
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    ABSTRACT: Rheumatoid arthritis synovial fibroblasts (RA-SFs) show an aggressive phenotype and support joint inflammation and tissue destruction. New druggable targets in RA-SFs would therefore be of high therapeutic interest. The present study shows that the intermediate-conductance, calcium-activated potassium channel KCa3.1 (KCNN4) is expressed at the mRNA and protein level in RA-SFs, is functionally active, and has a regulatory impact on cell proliferation and secretion of pro-inflammatory and pro-destructive mediators. Whole-cell patch-clamp recordings identified KCa3.1 as the dominant potassium channel in the physiologically relevant membrane voltage range below 0 mV. Stimulation with transforming growth factor β1 (TGF-β1) significantly increased transcription, translation, and channel function of KCa3.1. Inhibition of KCa3.1 by the selective, pore-blocking inhibitor TRAM-34, (and, in part by siRNA) significantly reduced cell proliferation, as well as expression and secretion of pro-inflammatory factors (IL-6, IL-8, and MCP1) and the tissue-destructive protease MMP3. These effects were observed in non-stimulated and/or TGF-β1-stimulated RA-SFs. Since small molecule-based interference with KCa3.1 is principally well tolerated in clinical settings, further evaluation of channel blockers in models of rheumatoid arthritis may be a promising approach to identify new pharmacological targets and develop new therapeutic strategies for this debilitating disease. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Full-text · Article · Dec 2014 · Journal of Cellular Physiology
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    • "gBK tumor antigen as therapeutic target for SCLC 201 Am J Transl Res 2014;6(3):188-205 RCK2 regions. So these functional properties are consistent with other BK channel tracings [22]. Prolonged exposure to pimaric acid induced cell swelling within 20 minutes (Figure 3B); the specific BK channel inhibitor, iberiotoxin , prevented the pimaric acid-induced swelling . "
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    ABSTRACT: Big Potassium (BK) ion channels have several splice variants. One splice variant initially described within human glioma cells is called the glioma BK channel (gBK). Using a gBK-specific antibody, we detected gBK within three human small cell lung cancer (SCLC) lines. Electrophysiology revealed that functional membrane channels were found on the SCLC cells. Prolonged exposure to BK channel activators caused the SCLC cells to swell within 20 minutes and resulted in their death within five hours. Transduction of BK-negative HEK cells with gBK produced functional gBK channels. Quantitative RT-PCR analysis using primers specific for gBK, but not with a lung-specific marker, Sox11, confirmed that advanced, late-stage human SCLC tissues strongly expressed gBK mRNA. Normal human lung tissue and early, lower stage SCLC resected tissues very weakly expressed this transcript. Immunofluorescence using the anti-gBK antibody confirmed that SCLC cells taken at the time of the autopsy intensely displayed this protein. gBK may represent a late-stage marker for SCLC. HLA-A*0201 restricted human CTL were generated in vitro using gBK peptide pulsed dendritic cells. The exposure of SCLC cells to interferon-γ (IFN-γ) increased the expression of HLA; these treated cells were killed by the CTL better than non-IFN-γ treated cells even though the IFN-γ treated SCLC cells displayed diminished gBK protein expression. Prolonged incubation with recombinant IFN-γ slowed the in vitro growth and prevented transmigration of the SCLC cells, suggesting IFN-γ might inhibit tumor growth in vivo. Immunotherapy targeting gBK might impede advancement to the terminal stage of SCLC via two pathways.
    Full-text · Article · Oct 2014 · American Journal of Translational Research
    • "BK channels are expressed by many but not all cells in the body. Of interest, human embryonic kidney cells (HEK), Chinese hamster ovary (CHO) cells and oocytes don't display BK channels when analyzed by standard electrophysiological readings [31] [32]. These cell lines have proven invaluable in studying BK and other ion channels as they allow for the easy transfection of ion channel genes for functional assays. "
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    ABSTRACT: The Big Potassium (BK) ion channel is commonly known by a variety of names (Maxi-K, KCNMA1, slo, stretch-activated potassium channels, KCa1.1). Each name reflects a different physical property displayed by this single ion channel. This transmembrane channel is found on nearly every cell type of the body and has its own distinctive roles for that tissue type. The BKα channel contains the pore that releases potassium ions from intracellular stores. This ion channel is found on the cell membrane, endoplasmic reticulum, Golgi and mitochondria. Complex splicing pathways produce different isoforms. The BKα channels can be phosphorylated, palmitoylated and myristylated. BK is composed of a homo-tetramer that interacts with β and γ chains. These accessory proteins provide a further modulating effect on the functions of BKα channels. BK channels play important roles in cell division and migration. In this review, we will focus on the biology of the BK channel, especially its role, and its immune response towards cancer. Recent proteomic studies have linked BK channels with various proteins. Some of these interactions offer further insight into the role that BK channels have with cancers, especially with brain tumors. This review shows that BK channels have a complex interplay with intracellular components of cancer cells and still have plenty of secrets to be discovered.
    No preview · Article · Jul 2014 · International Immunopharmacology
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