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K Channels As Targets for Specific Immunomodulation

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K Channels As Targets for Specific Immunomodulation Review TRENDS in Pharmacological Sciences Vol.25 No.5 May 2004 K1 channels as targets for specific immunomodulation K. George Chandy1, Heike Wulff2, Christine Beeton1, Michael Pennington3, George A. Gutman1 and Michael D. Cahalan1 1Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA 2Department of Pharmacology and Toxicology, University of California, Davis, CA 95616, USA 3Bachem Bioscience, King of Prussia, PA 19406, USA 21 The voltage-gated Kv1.3 channel and the Ca -activated gene encodes the lymphocyte KV channel [8,9].An IKCa1 K1 channel are expressed in T cells in a distinct intermediate-conductance Ca2þ-activated Kþ channel pattern that depends on the state of lymphocyte acti- was identified in T cells in 1992 [10–12], and shown to vation and differentiation. The channel phenotype be a product of the KCNN4 (IKCa1, KCa3.1; http://www. changes during the progression from the resting to the iuphar-db.org/iuphar-ic/KCa.html) gene in 1997 [13]. activated cell state and from naı¨ve to effector memory Subsequent studies by our group identified calmodulin cells, affording promise for specific immunomodulatory as the Ca2þ sensor of the IKCa1 channel [14]. The salient actions of K1 channel blockers. In this article, we review features of both channels were summarized in a recent the functional roles of these channels in both naı¨ve cells review [15]. and memory cells, describe the development of selec- Following the discovery that Kþ channels are essential tive inhibitors of Kv1.3 and IKCa1 channels, and provide for T-cell function, several other Kþ channels have been a rationale for the potential therapeutic use of these implicated in the proliferation of a wide variety of normal inhibitors in immunological disorders. and malignant cells (Figure 1b). In this review, we define the physiological roles of Kv1.3 and IKCa1 channels in In the 1950s, James Gowans’ research group defined the T cells, describe the development of increasingly selective central role of lymphocytes in immune responses, and in channel inhibitors and discuss the rationale for their the 1960s the seminal work of Jacques Miller and Robert possible use as therapeutic immunomodulators. Good and their colleagues elucidated the crucial role of thymus-derived lymphocytes (T cells). Ionic movements Physiological roles of Kv1.3 and IKCa1 channels in T cells associated with mitogen activation of lymphocytes were Molecular interactions at the immunological synapse first reported in the 1970s [1], but ion channels and The T-cell-mediated immune response is initiated by electrophysiological studies were far removed from the recognition of processed antigenic peptide bound to consciousness of immunologists during this period, being major histocompatibility complex (MHC) proteins on the domain of those investigating excitable cells (nerves antigen-presenting cells (APCs) by the antigen-specific and muscles). This barrier was breached in 1984 with multi-subunit T-cell receptor (TCR)–CD3 complex on the first patch-clamp studies on Kþ channels in T cells (Figure 2). Within minutes the TCR–CD3 complex lymphocytes [2–4], and during the past two decades and accessory proteins cluster at the zone of contact with there has been a steady growth of publications in this the APC in a region termed the ‘immunological synapse’ research area (Figure 1a). (IS). Antigen-induced redistribution of key receptors and In addition to characterizing the biophysical properties signaling molecules at the IS facilitates transduction of of the voltage-gated KV channel in T cells, we showed that signals that activate T cells. A recent fluorescence these channels are important for T-cell activation by demon- resonance energy transfer (FRET) study in lymphocytes strating that several chemically unrelated Kþ channel transfected with Kv1.3 channels showed that the channel blockers suppressed proliferation and cytokine production was in close proximity to CD3 [16]. Biochemical exper- with potenciesparallelingchannelblockade[2,5]. Theseren- iments [17–22] also suggest that the Kv1.3 channel is part dipitous discovery in 1989 that charybdotoxin (ChTX), a of a signaling complex that includes enzymes [tyrosine lck peptide from the venom of the scorpion Leiurus quinques- kinase p56 and protein kinase C (PKC)], adaptor triatus, blocks the KV channel at nanomolar concen- proteins [Kvb2 and hDlg (human homolog of the Droso- trations [6] led to the isolation of increasingly potent and phila discs large tumor suppressor protein), PSD-95 selective channel inhibitors from scorpion venom, sea (postsynaptic density 95), ZIP-1 (Zrt/Irt-like protein) and anemone extracts and plants [7]. The pace of discovery ZIP2] and the accessory protein CD4. Tyrosine phos- accelerated with the demonstration that the KCNA3 phorylation of Kv1.3 channels and modulation of Kv1.3 lck (Kv1.3; http://www.iuphar-db.org/iuphar-ic/KV1x.html) channel currents by p56 further suggests that the clustering of Kv1.3 channels and p56lck could provide a Corresponding author: K. George Chandy ([email protected]). mechanism for regulating channel function [17–19,21,22]. www.sciencedirect.com 0165-6147/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tips.2004.03.010 Review TRENDS in Pharmacological Sciences Vol.25 No.5 May 2004 281 (a) Lymphocytes and K+ channels Myelin-reactive T cells from MS high patients are Kv1.3 TEM cells [56]; Kv1.3 in proximity to CD3 [16] Kv1.3 blockade treats EAE [59] 400 CaM and IKCa1 [14]; correolide [46] 350 ShK [32] 300 MgTX [35] HERG in leukemia [67] IKCa1high in T-cell activation [58]; 250 TRAM34 [51] Kv1.3 cloned [8,9] 200 IKCa1 cloned [11]; ChTX blocks MgTX in vivo [36] 150 KV in T cells [6] T cells patch-clamped; 100 K channels essential in Cumulative number of publications number Cumulative V K+ channels in T-cell Ca2+ signaling [11,30,64]; K+ fluxes T-cell proliferation [2–5] K channels in T cells [11,65] 50 in thymocytes [1] Ca KV and KCa channels in B-cell activation [66] 0 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 Year of publication (b) K+ channels and proliferation 400 Hepatic carcinoma [81]; 350 vascular restenosis [54] 300 Oncogenic potential 250 of EAG [76]; colon cancer [77] 200 Glia, GH4 [70]; Gastric wound repair [78]; 150 small-cell lung neoplastic hematopoietic cells [79]; cancer [71] vascular smooth muscle cells [80] 100 Fibroblasts [68] B cells [69] Cumulative number of publications number Cumulative T cells [2] 50 Prostate cancer [74]; astrocytoma [75] 0 Brown fat cells [72]; myeloblastic leukemia [73] 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 Year of publication TRENDS in Pharmacological Sciences Figure 1. The cumulative number of publications as of November 2003 on (a) ‘lymphocytes and Kþ channels’ and (b) ‘Kþ channels and proliferation’. Key discoveries in both fields are highlighted. Abbreviations: CaM, calmodulin; ChTX, charybdotoxin; EAE, experimental autoimmune encephalomyelitis; EAG, ether a-go-go; IKCa1, intermediate-conductance Ca2þ-activated Kþ channel subtype 1; HERG, human ether-a` -go-go-related gene; Kv1.3high, high levels of Kv1.3 channels; MgTX, margatoxin; MS, multiple sclerosis; ShK, Stichodactyla helianthus toxin; TEM cells, effector memory T cells. (Data are from [1–6,8,9,11,14,16,30,32,35,36,46,51,54,56,58,59,64–81].) Clustering interactions of Kv1.4 channels with PSD-95 inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] and diacylgly- inhibit the internalization of Kv1.4 channels [23] and the cerol, which induce the release of Ca2þ from internal same could be true for Kv1.3 channels. Because CD4 and stores, and the activation of PKC. Depletion of internal CD3 aggregate at the IS, it is conceivable that the Ca2þ stores causes voltage-independent Ca2þ release- envisaged CD4–Kv1.3 channel complex localizes at the activated Ca2þ (CRAC) channels to open in the membrane, IS and regulates early events in T-cell activation. A recent and the ensuing Ca2þ influx sustains elevated levels of study of cytotoxic T cells transfected with Kv1.3 channels cytosolic Ca2þ. The physiological significance of the Ca2þ supports this notion by demonstrating clustering of Kv1.3 signal mediated by CRAC channels is highlighted by their channels at the site of interaction of cytotoxic T cells with absence in severe-combined immunodeficiency patients the target cell [24]. The Kv1.3 channel has also been [26,27] and by the requirement of sustained Ca2þ influx reported to be physically and functionally coupled to b1- for 75% of new gene expression via the phosphatase integrins [25] that stabilize the IS and are also important calcineurin [27,28]. Coordinated activity of Ca2þ- and in lymphocyte adhesion and migration. PKC-dependent signaling pathways culminates in cell proliferation. Kþ channels and Ca2þ signaling Kv1.3 and IKCa1 channels regulate Ca2þ signaling The activation events following T-cell engagement with events via the control of membrane potential [15,22].Ca2þ antigen and the role of Kv1.3 and IKCa1 channels in this influx through CRAC channels is reduced at depolarized signaling cascade are shown in Figure 2 [15,22]. Antigen potentials and consequently membrane depolarization recognition leads to the activation of tyrosine kinases and attenuates the Ca2þ signal. The driving force for Ca2þ phospholipase C (PLC), resulting in the generation of entry is restored by membrane hyperpolarization brought www.sciencedirect.com 282 Review TRENDS in Pharmacological Sciences Vol.25 No.5 May 2004 APC MHC class II CD80, CD86 VCAM-4 CD4 Antigen CD28 K+ Ca2+ CD3 CD3 β αβ 1-integrin ε δ γ ε Kv1.3 CRAC hDlg (PDZ) p56lck Ins(1,4,5)P3 Kvβ2 ZIP-1/2 PKC PLC [Ca2+]↑ Ca2+ stores CaM Ras JNK Calcineurin CaM IKCa1 + K Transcription, NFAT IL-2 production, T-cell proliferation TRENDS in Pharmacological Sciences Figure 2.
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