Joanna Bielanska

Immunomodulatory effects of diclofenac in leukocytes through the targeting of Kv1.3 voltage-dependent potassium channels.

Kv1.3 plays a crucial role in the activation and proliferation of T-lymphocytes and macrophages. While Kv1.3 is responsible for the voltage-dependent potassium current in T-cells, in macrophages this K(+) current is generated by the association of Kv1.3 and Kv1.5. Patients with autoimmune diseases show a high number of effector memory T cells that are characterized by a high expression of Kv1.3 and Kv1.3 antagonists ameliorate autoimmune disorders in vivo. Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) used in patients who suffer from painful autoimmune diseases such as rheumatoid arthritis. In this study, we show that diclofenac impairs immune response via a mechanism that involves Kv1.3. While diclofenac inhibited Kv1.3 expression in activated macrophages and T-lymphocytes, Kv1.5 remained unaffected. Diclofenac also decreased iNOS levels in Raw 264.7 cells, impairing their activation in response to lipopolysaccharide (LPS). LPS-induced macrophage migration and IL-2 production in stimulated Jurkat T-cells were also blocked by pharmacological doses of diclofenac. These effects were mimicked by Margatoxin, a specific Kv1.3 inhibitor, and Charybdotoxin, which blocks both Kv1.3 and Ca(2+)-activated K(+) channels (K(Ca)3.1). Because Kv1.3 is a very good target for autoimmune therapies, the effects of diclofenac on Kv1.3 are of high pharmacological relevance.

Voltage-dependent potassium channels Kv1.3 and Kv1.5 in human cancer.

Membrane ion channels participate in cancerous processes such as proliferation, migration and invasion, which contribute to metastasis. Increasing evidence indicates that voltage-dependent K(+) (Kv) channels are involved in the proliferation of many types of cells, including tumor cells. Kv channels have generated immense interest as a promising tool for developing new anti-tumor therapies. Therefore, the identification of potential biomarkers and therapeutic targets in specific cancers is an important prerequisite for the treatment. Since Kv1.3 and Kv1.5 are involved in the proliferation of many mammalian cells, we aimed to study the expression of Kv1.3 and Kv1.5 in a plethora of human cancers. Thus, tissues from breast, stomach, kidney, bladder, lung, skin, colon, ovary, pancreas, brain, lymph node, skeletal muscle and some of their malignant counterparts have been analyzed. Whereas Kv1.3 expression was either decreased or did not change in most tumors, Kv1.5 was overexpressed. However, the presence of Kv1.3 was mostly associated with inflammatory lymphoplasmocytic cells. Independent of the suitability of individual channels as therapeutic targets, the identification of a Kv phenotype from tumor specimens could have a diagnostic value of its own. Our results demonstrate that Kv1.5, and to some extent Kv1.3, are aberrantly expressed in a number of human cancers. These channels could serve both as novel markers of the metastatic phenotype and as potential new therapeutic targets. The concept of Kv channels as therapeutic targets or prognostic biomarkers attracts increasing interest and warrants further investigation.

Immunomodulation of voltage-dependent K+ channels in macrophages: molecular and biophysical consequences

Voltage-dependent potassium (Kv) channels play a pivotal role in the modulation of macrophage physiology. Macrophages are professional antigen-presenting cells and produce inflammatory and immunoactive substances that modulate the immune response. Blockage of Kv channels by specific antagonists decreases macrophage cytokine production and inhibits proliferation. Numerous pharmacological agents exert their effects on specific target cells by modifying the activity of their plasma membrane ion channels. Investigation of the mechanisms involved in the regulation of potassium ion conduction is, therefore, essential to the understanding of potassium channel functions in the immune response to infection and inflammation. Here, we demonstrate that the biophysical properties of voltage-dependent K+ currents are modified upon activation or immunosuppression in macrophages. This regulation is in accordance with changes in the molecular characteristics of the heterotetrameric Kv1.3/Kv1.5 channels, which generate the main Kv in macrophages. An increase in K+ current amplitude in lipopolysaccharide-activated macrophages is characterized by a faster C-type inactivation, a greater percentage of cumulative inactivation, and a more effective margatoxin (MgTx) inhibition than control cells. These biophysical parameters are related to an increase in Kv1.3 subunits in the Kv1.3/Kv1.5 hybrid channel. In contrast, dexamethasone decreased the C-type inactivation, the cumulative inactivation, and the sensitivity to MgTx concomitantly with a decrease in Kv1.3 expression. Neither of these treatments apparently altered the expression of Kv1.5. Our results demonstrate that the immunomodulation of macrophages triggers molecular and biophysical consequences in Kv1.3/Kv1.5 hybrid channels by altering the subunit stoichiometry.

Developmental Switch of the Expression of Ion Channels in Human Dendritic Cells

Modulation of the expression and activity of plasma membrane ion channels is one of the mechanisms by which immune cells can regulate their intracellular Ca2+ signaling pathways required for proliferation and/or differentiation. Voltage-gated K+ channels, inwardly rectifying K+ channels, and Ca2+-activated K+ channels have been described to play a major role in controlling the membrane potential in lymphocytes and professional APCs, such as monocytes, macrophages, and dendritic cells (DCs). Our study aimed at the characterization and identification of ion channels expressed in the course of human DC differentiation from monocytes. We report in this study for the first time that immature monocyte-derived DCs express voltage-gated Na+ channels in their plasma membrane. The analysis of the biophysical and pharmacological properties of the current and PCR-based cloning revealed the presence of Nav1.7 channels in immature DCs. Transition from the immature to a mature differentiation state, however, was accompanied by the down-regulation of Nav1.7 expression concomitant with the up-regulation of voltage-gated Kv1.3 K+ channel expression. The presence of Kv1.3 channels seems to be common for immune cells; hence, selective Kv1.3 blockers may emerge as candidates for inhibiting various functions of mature DCs that involve their migratory, cytokine-secreting, and T cell-activating potential.

The voltage-dependent K+ channels Kv1.3 and Kv1.5 in human cancer

Voltage-dependent K+ channels (Kv) are involved in a number of physiological processes, including immunomodulation, cell volume regulation, apoptosis as well as differentiation. Some Kv channels participate in the proliferation and migration of normal and tumor cells, contributing to metastasis. Altered expression of Kv1.3 and Kv1.5 channels has been found in several types of tumors and cancer cells. In general, while the expression of Kv1.3 apparently exhibits no clear pattern, Kv1.5 is induced in many of the analyzed metastatic tissues. Interestingly, evidence indicates that Kv1.5 channel shows inversed correlation with malignancy in some gliomas and non-Hodgkins lymphomas. However, Kv1.3 and Kv1.5 are similarly remodeled in some cancers. For instance, expression of Kv1.3 and Kv1.5 correlates with a certain grade of tumorigenicity in muscle sarcomas. Differential remodeling of Kv1.3 and Kv1.5 expression in human cancers may indicate their role in tumor growth and their importance as potential tumor markers. However, despite of this increasing body of information, which considers Kv1.3 and Kv1.5 as emerging tumoral markers, further research must be performed to reach any conclusion. In this review, we summarize what it has been lately documented about Kv1.3 and Kv1.5 channels in human cancer.

Targeting the Voltage-Dependent K+ Channels Kv1.3 and Kv1.5 as Tumor Biomarkers for Cancer Detection and Prevention

Potassium channels (KCh) are a diverse group of membrane proteins that participate in the control of the membrane potential. More than eighty different KCh genes have been identified, which are expressed in virtually all living cells. In addition to nerve and cardiac action potentials, these proteins are involved in a number of physiological processes, including cell volume regulation, apoptosis, immunomodulation and differentiation. Furthermore, many KCh have been reported to play a role in proliferation and cell cycle progression in mammalian cells, and an important number of studies report the involvement of KCh in cancer progression. The voltage dependent potassium (Kv) channels, in turn, form the largest family of human KCh, which comprises about 40 genes. Because Kv1.3 and Kv1.5 channels modulate proliferation of different mammalian cells, these proteins have been analyzed in a number of tumors and cancer cells. In most cancers, the expression patterns of Kv1.3 and Kv1.5 are remodeled, and in some cases, a correlation has been established between protein abundance and grade of tumor malignancy. The list of cancers evaluated is constantly growing, indicating that these proteins may be future targets for treatment. The aim of this review is to provide an updated overview of Kv1.3 and Kv1.5 channels during cancer development. Unlike Kv1.5, Kv1.3 is characterized by a very selective and potent pharmacology, which could lead to specific pharmacological targeting. Because potassium channels may play a pivotal role in tumor cell proliferation, these proteins should be taken into account when designing new cancer treatment strategies.

Impact of KCNE subunits on KCNQ1 (Kv7.1) channel membrane surface targeting

The KCNQ1 (Kv7.1) channel plays an important role in cardiovascular physiology. Cardiomyocytes co‐express KCNQ1 with KCNE1‐5 proteins. KCNQ1 may co‐associate with multiple KCNE regulatory subunits to generate different biophysically and pharmacologically distinct channels. Increasing evidence indicates that the location and targeting of channels are important determinants of their function. In this context, the presence of K+ channels in sphingolipid–cholesterol‐enriched membrane microdomains (lipid rafts) is under investigation. Lipid rafts are important for cardiovascular functioning. We aimed to determine whether KCNE subunits modify the localization and targeting of KCNQ1 channels in lipid rafts microdomains. HEK‐293 cells were transiently transfected with KCNQ1 and KCNE1–5, and their traffic and presence in lipid rafts were analyzed. Only KCNQ1 and KCNE3, when expressed alone, co‐localized in raft fractions. In addition, while KCNE2 and KCNE5 notably stained the cell surface, KCNQ1 and the rest of the KCNEs showed strong intracellular retention. KCNQ1 targets multiple membrane surface microdomains upon association with KCNE peptides. Thus, while KCNQ1/KCNE1 and KCNQ1/KCNE2 channels target lipid rafts, KCNQ1 associated with KCNE3–5 did not. Channel membrane dynamics, analyzed by fluorescence recovery after photobleaching (FRAP) experiments, further supported these results. In conclusion, the trafficking and targeting pattern of KCNQ1 can be influenced by its association with KCNEs. Since KCNQ1 is crucial for cardiovascular physiology, the temporal and spatial regulations that different KCNE subunits may confer to the channels could have a dramatic impact on membrane electrical activity and putative endocrine regulation. J. Cell. Physiol. 225: 692–700, 2010.

Emerging role for the voltage-dependent K+ channel Kv1.5 in B-lymphocyte physiology: expression associated with human lymphoma malignancy

Kv, which play a role in the immune system, are remodeled during carcinogenesis. Leukocytes present a limited Kv repertoire, with Kv1.3 and Kv1.5 as isoforms that are involved in neoplastic processes, such as proliferation and migration. In this study, we identified Kv1.5 in B‐lymphocytes, characterized its role in proliferation and migration, and analyzed Kv1.3 and Kv1.5 expression in human non‐Hodgkin lymphomas. DLBCL, F, MCL, ALCL, and T, along with control N specimens, were analyzed. Kv1.3 and Kv1.5 were found to be remodeled differentially; whereas Kv1.3 expression did not correlate with the state of dedifferentiation or the nature of lymphomatous cells, Kv1.5 abundance correlated inversely with clinical aggressiveness. Whereas indolent F expressed noticeable levels of Kv1.5, aggressive DLBCL showed low Kv1.5 levels. In addition, control LNs expressed heterogeneous high levels of Kv1.3, which could indicate some reactivity, whereas Kv1.5 abundance was low and quite homogeneous. Our data show that Kv1.5 is a determinant of human B cell proliferation and migration, thereby identifying this channel as a new target for immunomodulation. Our work also provides new insights into the use of Kv1.3 and Kv1.5 as potential targets during tumorigenesis.

Voltage-dependent Potassium Channels Kv1.3 and Kv1.5 in Human Fetus

Voltage-dependent K+ channels (Kv) control repolarization and membrane potential in electrically excitable cells. In addition, Kv channels are involved in the maintenance of vascular smooth muscle tone, insulin release, epithelial K+ transport, cell proliferation and leukocyte activation. Kv1.3 and Kv1.5 are widely distributed throughout the body and are involved in a variety of physiological processes taking place in the immune system, brain and muscle. Since the developmental pattern of Kv channels has an essential role in the maturing human, we aimed to study Kv1.3 and Kv1.5 channels in 8-10 week human fetal tissues. We chose that gestational age because all organs are in place and the nervous system, although not fully developed. However, the human embryo is undergoing major changes, which will lead to a defined adult pattern. Our results indicated that numerous tissues expressed Kv1.3 and Kv1.5. While Kv1.3 overlapped with the central and peripheral nervous systems, Kv1.5 was mostly localized in the central nervous system. In addition, both channels were abundantly expressed in the hematopoietic fetal liver. Finally, Kv1.5 heavily stained skeletal muscle and heart, whereas Kv1.3 was slightly present. This is the first study to analyze Kv1.3 and Kv1.5 in human during the beginning of fetal development.

Caveolar targeting links Kv1.3 with the insulin-dependent adipocyte physiology

The voltage-dependent potassium channel Kv1.3 participates in peripheral insulin sensitivity. Genetic ablation of Kv1.3 triggers resistance to diet-induced weight gain, thereby pointing to this protein as a pharmacological target for obesity and associated type II diabetes. However, this role is under intense debate because Kv1.3 expression in adipose tissue raises controversy. We demonstrated that Kv1.3 is expressed in white adipose tissue from humans and rodents. Moreover, other channels, such as Kv1.1, Kv1.2, Kv1.4 and especially Kv1.5, from the same Shaker family are also present. Although elevated insulin levels and adipogenesis remodel the Kv phenotype, which could lead to multiple heteromeric complexes, Kv1.3 markedly participates in the insulin-dependent regulation of glucose uptake in mature adipocytes. Adipocyte differentiation increased the expression of Kv1.3, which is targeted to caveolae by molecular interactions with caveolin 1. Using a caveolin 1-deficient 3T3-L1 adipocyte cell line, we demonstrated that the localization of Kv1.3 in caveolar raft structures is important for proper insulin signaling. Insulin-dependent phosphorylation of the channel occurs at the onset of insulin-mediated signaling. However, when Kv1.3 was spatially outside of these lipid microdomains, impaired phosphorylation was exhibited. Our data shed light on the putative role of Kv1.3 in weight gain and insulin-dependent responses contributing to knowledge about adipocyte physiology.