Kv1.3-dependent immune system activation is regulated by KCNE4

Kv1.3 is a voltage-gated potassium channel that regulates leukocyte physiology. The association of Kv1.3 with the regulatory subunit KCNE4 fine-tunes the channel's activity. KCNE4 is a transmembrane protein that interacts with Kv1.3 through both of their cytoplasmic C-terminal ends. The protein regulates the membrane trafficking of the channel, affecting the magnitude of the currents and the C-type inactivation. Anomalies in Kv1.3 activity cause several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, or multiple sclerosis. Therefore, the therapeutic relevance of Kv1.3 postulates KCNE4 as a potential modulator of the immune system physiology. In this study, we investigated the effect of KCNE4 on the activity of Kv1.3 in different leukocyte cell lines. We analyzed the expression of KCNE4 in a model of Jurkat T-lymphocytes and in CY15 dendritic antigen-presenting cells. Dendritic cells exhibit a high expression of the ancillary peptide. Manipulation of KCNE4 abundance affected the Kv1.3-dependent T cell physiology, having an impact on the channel's translocation to the immunological synapse (IS) and IL-2 production. In CY15 cells, activation with LPS increased the Kv1.3/KCNE4 ratio and the current density of the cells. The oligomeric Kv1.3-KCNE4 channel has a variable stoichiometry as demonstrated by single fluorescence bleaching steps. Each tetramer can bind up to four molecules of KCNE4, affecting plasma membrane trafficking and current density of Kv1.3 in a progressive manner. Contrarily, a single KCNE4 subunit was able to enhance the C-type inactivation of the channel. Our results prove that KCNE4 acts as a regulatory element in Kv1.3-dependent immune system physiology. Kv1.3 is differentially modulated by the KCNE4 availability influencing the Kv1.3/KCNE4 architecture of the oligomeric channel and its physiological function. Supported by the Ministerio de Ciencia e Innovación (MICINN/AEI), Spain (PID2020-112647RB-I00 and 10.13039/501100011033) and European Regional Development Fund (FEDER).