TRESK potassium channel in human T lymphoblasts

A role for TASK2 channels in the human immunological synapse

The immunological synapse is a transient junction that occurs when the plasma membrane of a T cell comes in close contact with an APC after recognizing a peptide from the antigen-MHC. The interaction starts when CRAC channels embedded in the T cell membrane open, flowing calcium ions into the cell. To counterbalance the ion influx and subsequent depolarization, K_v 1.3 and KCa3.1 channels are recruited to the immunological synapse, increasing the extracellular K⁺ concentration. These processes are crucial as they initiate gene expression that drives T cell activation and proliferation. The T cell-specific function of the K_2P channel family member TASK2 channels and their role in autoimmune processes remains unclear. Using mass spectrometry analysis together with epifluorescence and super-resolution single-molecule localization microscopy, we identified TASK2 channels as novel players recruited to the immunological synapse upon stimulation. TASK2 localizes at the immunological synapse, upon stimulation with CD3 antibodies, likely interacting with these molecules. Our findings suggest that, together with K_v 1.3 and KCa3.1 channels, TASK2 channels contribute to the proper functioning of the immunological synapse, and represent an interesting treatment target for T cell-mediated autoimmune disorders.

Altered expression and functional role of ion channels in leukemia: bench to bedside

Leukemic cells' (LCs) survival, proliferation, activation, differentiation, and invasiveness/migration can be mediated through the function of cation and anion channels that are involved in volume regulation, polarization, cytoskeleton, and extracellular matrix reorganization. This study will review the expression of ion channels in LCs and their possible function in leukemia progression. We searched relevant literature by a PubMed (2002-2019) of English-language literature using the terms "ion channels", "leukemia", "proliferation", "differentiation", "apoptosis", and "migration". Altered expression and dysfunction of ion channels can have a strong impact on hematopoietic cell and LCs physiology and signaling, which contributes to the vital processes such as proliferation, differentiation, and apoptosis. Indeed, it can be stated that changing expression of ion channels can affect the onset and progression as well as clinical features and therapeutic responses of leukemia via inducing the maintenance of LCs. Since ion channels are membrane proteins, they can be easily accessible in LCs for understanding their influence on leukemia progression. On the other hand, ion channels can be new potential targets for chemotherapeutic agents, which may open a novel clinical and pharmaceutical field in leukemia therapy.

Changes in the expression of the potassium channels TASK1, TASK3 and TRESK in a rat model of oral squamous cell carcinoma and their relation to malignancy

OBJECTIVES

Potassium channels have been proposed to promote cancer cell proliferation and metastases. Thus, we investigated the expression pattern of three 2-pore domain potassium channels (K2Ps) TASK1, TASK3 and TRESK in advanced oral squamous cell carcinoma (OSCC), the commonest oral malignancy.

DESIGN

We used 4-nitroquinoline-1-oxide (4-NQO) to induce high grade OSCC in male adult rats. We then used immunohistochemistry and Western blotting to study the distribution and expression pattern of TASK1, TASK3 and TRESK in normal versus cancerous tissue. We also examined the expression of β-tubulin III (β-tub3), a marker associated with resistance to taxane-based chemotherapy and poor patient prognosis, and its correlation with the K2Ps. Finally, we studied the expression of TASK1, TASK3 and TRESK in human samples of SCC of oral origin.

RESULTS

We found that TASK3 was significantly up-regulated whereas TASK1 and TRESK were both significantly down-regulated in advanced, poorly differentiated OSCC. Both, rat and human SCC showed a significant increase in the expression of β-tub3. Interestingly, the expression of the latter correlated positively and significantly with TASK3 and TRESK but not TASK1 in rat OSCC. Our initial results showed a similar pattern of up and down regulation and correlation with β-tub3 for these three K2Ps in human SCC.

CONCLUSIONS

The changes in expression and the co-localization with a marker of resistance to taxanes like β-tub3 turn TASK1, TASK3 and TRESK into potentially new prognostic tools and possibly new therapeutic targets for OSCC.

Human T cells in silico: Modelling dynamic intracellular calcium and its influence on cellular electrophysiology

A network of ion currents influences basic cellular T cell functions. After T cell receptor activation, changes in highly regulated calcium levels play a central role in triggering effector functions and cell differentiation. A dysregulation of these processes might be involved in the pathogenesis of several diseases. We present a mathematical model based on the NEURON simulation environment that computes dynamic calcium levels in combination with the current output of diverse ion channels (K_V1.3, K_Ca3.1, K_2P channels (TASK1-3, TRESK), VRAC, TRPM7, CRAC). In line with experimental data, the simulation shows a strong increase in intracellular calcium after T cell receptor stimulation before reaching a new, elevated calcium plateau in the T cell's activated state. Deactivation of single ion channel modules, mimicking the application of channel blockers, reveals that two types of potassium channels are the main regulators of intracellular calcium level: calcium-dependent potassium (K_Ca3.1) and two-pore-domain potassium (K_2P) channels.

Cholinergic Machinery as Relevant Target in Acute Lymphoblastic T Leukemia

Various types of non-neuronal cells, including tumors, are able to produce acetylcholine (ACh), which acts as an autocrine/paracrine growth factor. T lymphocytes represent a key component of the non-neuronal cholinergic system. T cells-derived ACh is involved in a stimulation of their activation and proliferation, and acts as a regulator of immune response. The aim of the present work was to summarize the data about components of cholinergic machinery in T lymphocytes, with an emphasis on the comparison of healthy and leukemic T cells. Cell lines derived from acute lymphoblastic leukemias of T lineage (T-ALL) were found to produce a considerably higher amount of ACh than healthy T lymphocytes. Additionally, ACh produced by T-ALL is not efficiently hydrolyzed, because acetylcholinesterase (AChE) activity is drastically decreased in these cells. Up-regulation of muscarinic ACh receptors was also demonstrated at expression and functional level, whereas nicotinic ACh receptors seem to play a less important role and not form functional channels in cells derived from T-ALL. We hypothesized that ACh over-produced in T-ALL may act as an autocrine growth factor and play an important role in leukemic clonal expansion through shaping of intracellular Ca²⁺ signals. We suggest that cholinergic machinery may be attractive targets for new drugs against T-ALL. Specifically, testing of high affinity antagonists of muscarinic ACh receptors as well as antagomiRs, which interfere with miRNAs involved in the suppression of AChE expression, may be the first choice options.

Placing ion channels into a signaling network of T cells: from maturing thymocytes to healthy T lymphocytes or leukemic T lymphoblasts

T leukemogenesis is a multistep process, where the genetic errors during T cell maturation cause the healthy progenitor to convert into the leukemic precursor that lost its ability to differentiate but possesses high potential for proliferation, self-renewal, and migration. A new misdirecting "leukemogenic" signaling network appears, composed by three types of participants which are encoded by (1) genes implicated in determined stages of T cell development but deregulated by translocations or mutations, (2) genes which normally do not participate in T cell development but are upregulated, and (3) nondifferentially expressed genes which become highly interconnected with genes expressed differentially. It appears that each of three groups may contain genes coding ion channels. In T cells, ion channels are implicated in regulation of cell cycle progression, differentiation, activation, migration, and cell death. In the present review we are going to reveal a relationship between different genetic defects, which drive the T cell neoplasias, with calcium signaling and ion channels. We suggest that changes in regulation of various ion channels in different types of the T leukemias may provide the intracellular ion microenvironment favorable to maintain self-renewal capacity, arrest differentiation, induce proliferation, and enhance motility.

Properties, regulation, pharmacology, and functions of the K₂p channel, TRESK

TWIK-related spinal cord K(+) channel (TRESK) is the gene product of KCNK18, the last discovered leak potassium K2P channel gene. Under resting conditions, TRESK is constitutively phosphorylated at two regulatory regions. Protein kinase A (PKA) and microtubule affinity-regulating (MARK) kinases can be applied in experiments to phosphorylate these sites of TRESK expressed in Xenopus oocytes, respectively. Upon generation of a calcium signal, TRESK is dephosphorylated and thereby activated by calcineurin. In this process, the binding of calcineurin to the channel by non-catalytic interacting sites is essential. The phosphorylation/dephosphorylation regulatory process is modified by 14-3-3 proteins. Human, but not murine TRESK is also activated by protein kinase C. TRESK is expressed most abundantly in sensory neurons of the dorsal root ganglia (DRG) and trigeminal ganglia, and the channel modifies certain forms of nociceptive afferentation. In a large pedigree, a dominant negative mutant TRESK allele was found to co-segregate perfectly with migraine phenotype. While this genetic defect may be responsible only for a very small fraction of migraine cases, specific TRESK activation is expected to exert beneficial effect in common forms of the disease.

Tubulin binds to the cytoplasmic loop of TRESK background K⁺ channel in vitro

The cytoplasmic loop between the second and third transmembrane segments is pivotal in the regulation of TRESK (TWIK-related spinal cord K+ channel, K2P18.1, KCNK18). Calcineurin binds to this region and activates the channel by dephosphorylation in response to the calcium signal. Phosphorylation-dependent anchorage of 14-3-3 adaptor protein also modulates TRESK at this location. In the present study, we identified molecular interacting partners of the intracellular loop. By an affinity chromatography approach using the cytoplasmic loop as bait, we have verified the specific association of calcineurin and 14-3-3 to the channel. In addition to these known interacting proteins, we observed substantial binding of tubulin to the intracellular loop. Successive truncation of the polypeptide and pull-down experiments from mouse brain cytosol narrowed down the region sufficient for the binding of tubulin to a 16 amino acid sequence: LVLGRLSYSIISNLDE. The first six residues of this sequence are similar to the previously reported tubulin-binding region of P2X2 purinergic receptor. The tubulin-binding site of TRESK is located close to the protein kinase A (PKA)-dependent 14-3-3-docking motif of the channel. We provide experimental evidence suggesting that 14-3-3 competes with tubulin for the binding to the cytoplasmic loop of TRESK. It is intriguing that the 16 amino acid tubulin-binding sequence includes the serines, which were previously shown to be phosphorylated by microtubule-affinity regulating kinases (MARK kinases) and contribute to channel inhibition. Although tubulin binds to TRESK in vitro, it remains to be established whether the two proteins also interact in the living cell.