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-Hodgkin's 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.

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.

Human glioma-initiating cells show a distinct immature phenotype resembling but not identical to NG2 glia.

Glioma-initiating cells (GICs) represent a potential important therapeutic target because they are likely to account for the frequent recurrence of malignant gliomas; however, their identity remains unsolved. Here, we characterized the cellular lineage fingerprint of GICs through a combination of electrophysiology, lineage marker expression, and differentiation assays of 5 human patient-derived primary GIC lines. Most GICs coexpressed nestin, NG2 proteoglycan, platelet-derived growth factor receptor-α, and glial fibrillary acidic protein. Glioma-initiating cells could be partially differentiated into astrocytic but not oligodendroglial or neural lineages. We also demonstrate that GICs have a characteristic electrophysiologic profile distinct from that of well-characterized tumor bulk cells. Together, our results suggest that GICs represent a unique type of cells reminiscent of an immature phenotype that closely resembles but is not identical to NG2 glia with respect to marker expression and functional membrane properties.

Increased voltage-dependent K+ channel Kv1.3 and Kv1.5 expression correlates with leiomyosarcoma aggressiveness.

Voltage-dependent K+ channels (Kv) are involved in the proliferation and differentiation of mammalian cells, since Kv antagonists impair cell cycle progression. Although myofibers are terminally differentiated, some myoblasts may re-enter the cell cycle and proliferate. Since Kv1.3 and Kv1.5 expression is remodeled during tumorigenesis and is involved in smooth muscle proliferation, the purpose of this study was to analyze the expression of Kv1.3 and Kv1.5 in smooth muscle neoplasms. In the present study, we examined human samples of smooth muscle tumors together with healthy specimens. Thus, leiomyoma (LM) and leiomyosarcoma (LMS) tumors were analyzed. Results showed that Kv1.3 was poorly expressed in the healthy muscle and indolent LM specimens, whereas aggressive LMS showed high levels of Kv1.3 expression. Kv1.5 staining was correlated with malignancy. The findings show a remodeling of Kv1.3 and Kv1.5 in human smooth muscle sarcoma. A correlation of Kv1.3 and Kv1.5 expression with tumor aggressiveness was observed. Thus, our results indicate Kv1.5 and Kv1.3 as potential tumorigenic targets for aggressive human LMS.

Differential expression of Kv1.3 and Kv1.5 voltage-dependent K+ channels in human skeletal muscle sarcomas.

Because Kv1.3 and Kv1.5 K(+) channels are remodeled during tumorigenesis and participate in skeletal muscle proliferation, we analyzed their expression in human skeletal muscle sarcomas. Aggressive alveolar rhabdomyosarcoma (ARMS) and embryonal rhabdomyosarcoma (ERMS) were studied. Kv1.5 expression was moderate in adult muscle and low in ERMS, whereas it was notable in ARMS and embryonic samples. Kv1.3 expression showed no major differences between RMS and healthy samples. We found a correlation of Kv1.3 and Kv1.5 expression with the tumor malignancy.

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.

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.

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

Voltage-dependent potassium (K(v)) 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 K(v) 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 K(v)1.3/K(v)1.5 channels, which generate the main K(v) 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 K(v)1.3 subunits in the K(v)1.3/K(v)1.5 hybrid channel. In contrast, dexamethasone decreased the C-type inactivation, the cumulative inactivation, and the sensitivity to MgTx concomitantly with a decrease in K(v)1.3 expression. Neither of these treatments apparently altered the expression of K(v)1.5. Our results demonstrate that the immunomodulation of macrophages triggers molecular and biophysical consequences in K(v)1.3/K(v)1.5 hybrid channels by altering the subunit stoichiometry.

Electron paramagnetic resonance oxygen image hypoxic fraction plus radiation dose strongly correlates with tumor cure in FSa fibrosarcomas.

PURPOSE: Tumor hypoxia has long been known to produce resistance to radiation. In this study, electron paramagnetic resonance (EPR) oxygen imaging was investigated for its power to predict the success of tumor control according to tumor oxygenation level and radiation dose. METHODS AND MATERIALS: A total of 34 EPR oxygen images were obtained from the legs of C3H mice bearing 0.5-cm(3) FSa fibrosarcomas under both normal (air breathing) and clamped tumor conditions. Under the same conditions as those during which the images were obtained, the tumors were irradiated to a variety of doses near the FSa dose at which 50% of tumors were cured. Tumor tissue was distinguished from normal tissue using co-registration of the EPR oxygen images with spin-echo magnetic resonance imaging of the tumor and/or stereotactic localization. The tumor voxel statistics in the EPR oxygen image included the mean and median partial pressure of oxygen and the fraction of tumor voxels below the specified partial pressure of oxygen values of 3, 6, and 10 mm Hg. Bivariate logistic regression analysis using the radiation dose and each of the EPR oxygen image statistics to determine which best separated treatment failure from success. RESULTS: The measurements of the dose at which 50% of tumors were cured were similar to those found in published data for this syngeneic tumor. Bivariate analysis of 34 tumors demonstrated that tumor cure correlated with dose (p = 0.004) and with a <10 mm Hg hypoxic fraction (p = 0.023). CONCLUSION: Our results have shown that, together, radiation dose and EPR image hypoxic fraction separate the population of FSa fibrosarcomas that are cured from those that fail, thus predicting curability.

In vivo spin trapping of nitric oxide from animal tumors.

Spin trapping/electron paramagnetic resonance (EPR) spectroscopy allows specific detection of nitric oxide (NO) generation, in vivo. However, in order to detect an EPR signal in living organism, usually a stimulation of immune system with LPS is used to achieve higher than physiological NO levels. Here, we report non-invasive spin trapping of NO in tumors of non-treated, living animals. EPR spectroscopy was performed at S-band to detect NO in Cloudman S91 melanoma tumors growing in the tail of living, syngeneic hosts-DBA/2 mice. Iron (II) N-(dithiocarboxy)sarcosine Fe2+(DTCS)(2) was used as the spin trap. The results were confirmed by X-band ex vivo study. A characteristic three-line spectrum of NO-Fe(DTCS)(2) (A(N)=13 G) was observed (n=4, out of total n=6) in non-treated tumors and in tumors of animals treated with l-arginine. Substrate availability did not limit the detection of NO by spin trapping. Half-life time of the NO-Fe(DTCS)(2) in tumor tissue was about 60 min. The feasibility of non-invasive spin trapping/EPR spectroscopic detection of NO generated in tumor tissue in living animals, without additional activation of the immune system, was demonstrated for the first time.