Ion channels are transmembrane proteins that conduct specific ions across biological membranes. Ion channels are present at the onset of many cellular processes, and their malfunction triggers severe pathologies. Potassium channels (KChs) share a highly conserved signature that is necessary to conduct K⁺ through the pore region. To be functional, KChs require an exquisite regulation of their subcellular location and abundance. A wide repertoire of signatures facilitates the proper targeting of the channel, fine-tuning the balance that determines traffic and location. These signature motifs can be part of the secondary or tertiary structure of the protein and are spread throughout the entire sequence. Furthermore, the association of the pore-forming subunits with different ancillary proteins forms functional complexes. These partners can modulate traffic and activity by adding their own signatures as well as by exposing or masking the existing ones. Post-translational modifications (PTMs) add a further dimension to traffic regulation. Therefore, the fate of a KCh is not fully dependent on a gene sequence but on the balance of many other factors regulating traffic. In this review, we assemble recent evidence contributing to our understanding of the spatial expression of KChs in mammalian cells. We compile specific signatures, PTMs, and associations that govern the destination of a functional channel.

Protein lipidation is one of the most common forms of posttranslational modification. This alteration couples different lipids, such as fatty acids, phospho- and glycolipids and sterols, to cellular proteins. Lipidation regulates different aspects of the protein’s physiology, including structure, stability and affinity for cellular membranes and protein–protein interactions. In this scenario, palmitoylation is the addition of long saturated fatty acid chains to amino acid residues of the proteins. The enzymes responsible for this modification are acyltransferases and thioesterases, which control the protein’s behavior by performing a series of acylation and deacylation cycles. These enzymes target a broad repertoire of substrates, including ion channels. Thus, protein palmitoylation exhibits a pleiotropic role by differential modulation of the trafficking, spatial organization and electrophysiological properties of ion channels. Considering voltage-gated ion channels (VGICs), dysregulation of lipidation of both the channels and the associated ancillary subunits correlates with the development of various diseases, such as cancer or mental disorders. Therefore, a major role for protein palmitoylation is currently emerging, affecting not only the dynamism and differential regulation of a moiety of cellular proteins but also linking to human health. Therefore, palmitoylation of VGIC, as well as related enzymes, constitutes a novel pharmacological tool for drug development to target related pathologies.

The voltage-gated potassium channel Kv1.3 plays an apparent dual physiological role by participating in activation and proliferation of leukocytes as well as promoting apoptosis in several types of tumor cells. Therefore, Kv1.3 is considered a potential pharmacological target for immunodeficiency and cancer. Different cellular locations of Kv1.3, at the plasma membrane or the mitochondria, could be responsible for such duality. While plasma membrane Kv1.3 facilitates proliferation, the mitochondrial channel modulates apoptotic signaling. Several molecular determinants of Kv1.3 drive the channel to the cell surface, but no information is available about its mitochondrial targeting. Caveolins, which are able to modulate cell survival, participate in the plasma membrane targeting of Kv1.3. The channel, via a caveolin-binding domain (CBD), associates with caveolin 1 (Cav1), which localizes Kv1.3 to lipid raft membrane microdomains. The aim of our study was to understand the role of such interactions not only for channel targeting but also for cell survival in mammalian cells. By using a caveolin association-deficient channel (Kv1.3 CBD_less), we demonstrate here that while the Kv1.3–Cav1 interaction is responsible for the channel localization in the plasma membrane, a lack of such interaction accumulates Kv1.3 in the mitochondria. Kv1.3 CBD_less severely affects mitochondrial physiology and cell survival, indicating that a functional link of Kv1.3 with Cav1 within the mitochondria modulates the pro-apoptotic effects of the channel. Therefore, the balance exerted by these two complementary mechanisms fine-tune the physiological role of Kv1.3 during cell survival or apoptosis. Our data highlight an unexpected role for the mitochondrial caveolin–Kv1.3 axis during cell survival and apoptosis.

The voltage-gated potassium channel Kv1.3 plays a pivotal role in a myriad of biological processes, including cell proliferation, differentiation, and apoptosis. Kv1.3 undergoes fine-tuned regulation, and its altered expression or function correlates with tumorigenesis and cancer progression. Moreover, posttranslational modifications (PTMs), such as phosphorylation, have evolved as rapid switch-like moieties that tightly modulate channel activity. In addition, kinases are promising targets in anticancer therapies. The diverse serine/threonine and tyrosine kinases function on Kv1.3 and the effects of its phosphorylation vary depending on multiple factors. For instance, Kv1.3 regulatory subunits (KCNE4 and Kvβ) can be phosphorylated, increasing the complexity of channel modulation. Scaffold proteins allow the Kv1.3 channelosome and kinase to form protein complexes, thereby favoring the attachment of phosphate groups. This review compiles the network triggers and signaling pathways that culminate in Kv1.3 phosphorylation. Alterations to Kv1.3 expression and its phosphorylation are detailed, emphasizing the importance of this channel as an anticancer target. Overall, further research on Kv1.3 kinase-dependent effects should be addressed to develop effective antineoplastic drugs while minimizing side effects. This promising field encourages basic cancer research while inspiring new therapy development.

The voltage-dependent potassium channel Kv1.3 plays essential roles in the immune system, participating in leukocyte activation, proliferation and apoptosis. The regulatory subunit KCNE4 acts as an ancillary peptide of Kv1.3, modulates K⁺currents and controls channel abundance at the cell surface. KCNE4-dependent regulation of the oligomeric complex fine-tunes the physiological role of Kv1.3. Thus, KCNE4 is crucial for Ca²⁺-dependent Kv1.3-related leukocyte functions. To better understand the role of KCNE4 in the regulation of the immune system, we manipulated its expression in various leukocyte cell lines. Jurkat T lymphocytes exhibit low KCNE4 levels, whereas CY15 dendritic cells, a model of professional antigen-presenting cells, robustly express KCNE4. When the cellular KCNE4 abundance was increased in T cells, the interaction between KCNE4 and Kv1.3 affected important T cell physiological features, such as channel rearrangement in the immunological synapse, cell growth, apoptosis and activation, as indicated by decreased IL-2 production. Conversely, ablation of KCNE4 in dendritic cells augmented proliferation. Furthermore, the LPS-dependent activation of CY15 cells, which induced Kv1.3 but not KCNE4, increased the Kv1.3-KCNE4 ratio and increased the expression of free Kv1.3 without KCNE4 interaction. Our results demonstrate that KCNE4 is a pivotal regulator of the Kv1.3 channelosome, which fine-tunes immune system physiology by modulating Kv1.3-associated leukocyte functions.

The voltage-dependent potassium (Kv) channel Kvβ family was the first identified group of modulators of Kv channels. Kvβ regulation of the α-subunits, in addition to their aldoketoreductase activity, has been under extensive study. However, scarce information about their specific α-subunit-independent biology is available. The expression of Kvβs is ubiquitous and, similar to Kv channels, is tightly regulated in leukocytes. Although Kvβ subunits exhibit cytosolic distribution, spatial localization, in close contact with plasma membrane Kv channels, is crucial for a proper immune response. Therefore, Kvβ2.1 is located near cell surface Kv1.3 channels within the immunological synapse during lymphocyte activation. The objective of this study was to analyze the structural elements that participate in the cellular distribution of Kvβs. It was demonstrated that Kvβ peptides, in addition to the cytoplasmic pattern, targeted the cell surface in the absence of Kv channels. Furthermore, Kvβ2.1, but not Kvβ1.1, targeted lipid raft microdomains in an S-acylation-dependent manner, which was concomitant with peptide localization within the immunological synapse. A pair of C-terminal cysteines (C301/C311) was mostly responsible for the specific palmitoylation of Kvβ2.1. Several insults altered Kvβ2.1 membrane localization. Therefore, growth factor-dependent proliferation enhanced surface targeting, whereas PKC activation impaired lipid raft expression. However, PSD95 stabilized Kvβ2.1 in these domains. This data shed light on the molecular mechanism by which Kvβ2.1 clusters into immunological synapses during leukocyte activation.