Fighting rheumatoid arthritis: Kv1.3 as a therapeutic target

Abstract Rheumatoid arthritis (RA) is a serious autoimmune disease that has severe impacts on both the wellbeing of patients and the economy of the health system. Similar to many autoimmune diseases, RA concurs with a long evolution, which eventually results in highly debilitating symptoms. Therapeutic treatments last for long periods during RA. However, their efficiency and side effects result in suboptimal conditions. Therefore, the need for specific, safer and nontoxic alternatives for the treatment of RA is essential. Kv1.3 is a voltage-gated potassium channel that has a crucial role in immune system response. The proliferation and activation of leukocytes are linked to differential expressions of this channel. The evidence is particularly relevant in the aggressive T effector memory (TEM) cells, which are the main actors in the development of autoimmune diseases. Blockage of Kv1.3 inhibits the reactivity of these cells. Furthermore, pharmacological inhibition of Kv1.3 ameliorates symptoms in animal models of autoimmune diseases, such as experimental autoimmune encephalomyelitis or induced psoriasis with no side effects. Kv1.3 is sensitive to several animal toxins and plant compounds, and several research groups have searched for new Kv1.3 blockers by improving these natural molecules. The research is mainly focused on enhancing the selectivity of the blockers, thereby reducing the potential for side effects on other related channel subunits. Higher selectivity means that treatments will potentially be less harmful. This leads to a lower discontinuation rate of the therapy than the current first-line treatment for RA. The molecular backgrounds of many autoimmune diseases implicate leukocyte Kv1.3 and suggests that a new medication for RA is feasible. Therapies could also be later repurposed to treat other immune system disorders

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

Heteromeric composition of the Kv 1.3 channelosome = Composició heteromèrica del canalosoma Kv1.3

[eng] Ion channels are transmembrane proteins containing aqueous pores which, once open, permit the pass of ions through the plasma membrane. This ion flux takes places following the electrochemical gradient for the specific ion. Kv1.3 is a voltage-gated potassium channel which is member of the Shaker superfamily. Its basic structure consists in a protein with six transmembrane domains, while the functional channel is formed by 4 copies of this protein. Kv1.3 participates in a great amount of physiological functions: nervous system, immune system, insulin signaling or cell proliferation. In the immune system, Kv1.3 is highly expressed both in lymphocytes as well as in mononuclear phagocytes. In both cell types, Kv1.3 regulates the immune activation and cell proliferation. Moreover, Kv1.3 is coexpressed with other ion channel proteins like Kv1.5 or KCNE4 in the immune cells. Kv1.5 is able to heteromerize with Kv1.3, generating heterotetramers with variable stoichiometries. Those heterotetramers produce intermediate phenotypes depending on the ratio of the subunits that generate them. On the other side, KCNE4 may interact with Kv1.3, but not with Kv1.5. Kv1.3 is greatly inhibited by the association with either of the two proteins. In the present thesis we focus in characterizing these interactions and the importance of stoichiometry in their effects. We demonstrate that the associations between Kv1.3 and Kv1.5; and between Kv1.3 and KCNE4 take place in immune cells. Moreover, by using a fusion protein we get to fix the stoichiometry of the Kv1.3-Kv1.5 complex to 1:1. With this stoichiometry, Kv1.5 acts as a dominant negative toward Kv1.3 in the complex. Further interactions are characterized by using several chimeric proteins. By using those chimaeras, it is revealed that the carboxyterminal domain is necessary for the correct function of the channel. On the other hand, we demonstrate that KCNE4 is able to interact with Kv1.3 regardless of Kv1.5 presence. Furthermore, the presence of Kv1.5 in the Kv1.3-KCNE4 interaction results in this association potentiating the function of the channel, instead of inhibiting it. These results are replicated both in heterologous systems as well as in native cells. This discovery presents a new paradigm by which the association with several modulatory proteins may result in the modification of the effect of each one of them. Taking into account the sheer number of different ion channel subunits, the number of different potential phenotypes is increased by a huge margin. KCNE1 is a regulatory subunit, as well as KCNE4. Unlike KCNE4, though, KCNE1 can interact with Kv1.5. In the present thesis we demonstrate for the first time that KCNE1 is not only able to associate with Kv1.5, but to potentiate its activity by a huge amount. This interaction also seems to affect the membrane microdomain targeting of Kv1.5 Finally, the 4 studied proteins are expressed in T lymphocytes, which are the main actors in the pathogenicity of autoimmune diseases. Therefore, we genotyped those genes in multiple sclerosis patients to identify different polymorphisms which could be linked to immune overactivity. After analyzing the different polymorphisms, we located some which could be of special relevance for the physiopathology of autoimmune diseases.[spa] Los canales iónicos son proteínas transmembrana que contienen poros acuosos que permiten el paso de iones a través de la membrana plasmática a favor de gradiente electroquímico. Kv1.3 es un canal de potasio dependiente de voltaje de la superfamilia Shaker. La estructura básica consiste en una proteína con seis dominios transmembrana y el canal funcional está formado por cuatro copias de esta proteína. Kv1.3 participa en multitud de funciones del organismo: sistema nervioso, sistema inmunitario, señalización de la insulina o proliferación celular. En el sistema inmunitario está altamente expresado tanto en linfocitos como en fagocitos mononucleares. En ambos tipos celulares regula la activación inmunitaria y la proliferación celular. Además, se ve coexpresado con otras proteínas de relevancia como Kv1.5 o KCNE4. Kv1.5 puede heteromerizar con Kv1.3, dando lugar a heterotrámeros de estequiometrias variables. Por otro lado, KCNE4 puede interaccionar con Kv1.3, pero no con Kv1.5. Kv1.3 se ve potentemente inhibido por ambas asociaciones. En la presente tesis nos centramos en caracterizar estas interacciones y el peso de la estequiometría en sus efectos. Demostramos que ambas asociaciones tienen lugar en células del sistema inmunitario. Además, mediante una proteína de fusión logramos fijar la estequiometría del complejo Kv1.3-Kv1-5 en 1:1. Así, Kv1.5 demuestra ejercer como dominante negativo respecto a Kv1.3 en el complejo. Estas interacciones intramoleculares son estudiadas mediante el uso de diversas proteínas quiméricas para dilucidar el peso de los extremos carboxiterminales en la formación del canal y su función. Por otro lado, demostramos que KCNE4 afecta el canal de estequiometría 1:1 aumentado su actividad, en lugar de reducirla. Este descubrimiento presenta un nuevo paradigma en que la asociación con varias proteínas reguladoras puede resultar en la modificación del efecto de cada una de ellas. KCNE1 es una proteína reguladora al igual que KCNE4, pero que interactúa con Kv1.5. En la presente tesis demostramos como KCNE1 no solo interacciona con Kv1.5, sino que aumenta en gran medida su actividad. Finalmente, también genotipamos estos genes en pacientes de una enfermedad autoinmune como es la esclerosis múltiple, llegando a localizar diversos polimorfismos de posible interés fisiopatológico

Calmodulin-dependent KCNE4 dimerization controls membrane targeting.

The voltage-dependent potassium channel Kv1.3 participates in the immune response. Kv1.3 is essential in diferent cellular functions, such as proliferation, activation and apoptosis. Because aberrant expression of Kv1.3 is linked to autoimmune diseases, fne-tuning its function is crucial for leukocyte physiology. Regulatory KCNE subunits are expressed in the immune system, and KCNE4 specifcally tightly regulates Kv1.3. KCNE4 modulates Kv1.3 currents slowing activation, accelerating inactivation and retaining the channel at the endoplasmic reticulum (ER), thereby altering its membrane localization. In addition, KCNE4 genomic variants are associated with immune pathologies. Therefore, an in-depth knowledge of KCNE4 function is extremely relevant for understanding immune system physiology. We demonstrate that KCNE4 dimerizes, which is unique among KCNE regulatory peptide family members. Furthermore, the juxtamembrane tetraleucine carboxyl-terminal domain of KCNE4 is a structural platform in which Kv1.3, Ca2+/calmodulin (CaM) and dimerizing KCNE4 compete for multiple interaction partners. CaM-dependent KCNE4 dimerization controls KCNE4 membrane targeting and modulates its interaction with Kv1.3. KCNE4, which is highly retained at the ER, contains an important ER retention motif near the tetraleucine motif. Upon escaping the ER in a CaM-dependent pattern, KCNE4 follows a COP-II-dependent forward trafcking mechanism. Therefore, CaM, an essential signaling molecule that controls the dimerization and membrane targeting of KCNE4, modulates the KCNE4-dependent regulation of Kv1.3, which in turn fne-tunes leukocyte physiology

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

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