K v 1.3 channel blockade with the Vm24 scorpion toxin attenuates the CD4 + effector memory T cell response to TCR stimulation.

BACKGROUND: In T cells, the Kv 1.3 and the KCa 3.1 potassium channels regulate the membrane potential and calcium homeostasis. Notably, during TEM cell activation, the number of Kv 1.3 channels on the cell membrane dramatically increases. Kv 1.3 blockade results in inhibition of Ca2+ signaling in TEM cells, thus eliciting an immunomodulatory effect. Among the naturally occurring peptides, the Vm24 toxin from the Mexican scorpion Vaejovis mexicanus is the most potent and selective Kv 1.3 channel blocker known, which makes it a promissory candidate for its use in the clinic. We have shown that addition of Vm24 to TCR-activated human T cells inhibits CD25 expression, cell proliferation and reduces delayed-type hypersensitivity reactions in a chronic inflammation model. Here, we used the Vm24 toxin as a tool to investigate the molecular events that follow Kv 1.3 blockade specifically on human CD4+ TEM cells as they are actively involved in inflammation and are key mediators of autoimmune diseases.

METHODS: We combined cell viability, activation, and multiplex cytokine assays with a proteomic analysis to identify the biological processes affected by Kv 1.3 blockade on healthy donors CD4+ TEM cells, following TCR activation in the presence or absence of the Vm24 toxin.

RESULTS: The peptide completely blocked Kv 1.3 channels currents without impairing TEM cell viability, and in response to TCR stimulation, it inhibited the expression of the activation markers CD25 and CD40L (but not that of CD69), as well as the secretion of the pro-inflammatory cytokines IFN-γ and TNF and the anti-inflammatory cytokines IL-4, IL-5, IL-9, IL-10, and IL-13. These results, in combination with data from the proteomic analysis, indicate that the biological processes most affected by the blockade of Kv 1.3 channels in a T cell activation context were cytokine-cytokine receptor interaction, mRNA processing via spliceosome, response to unfolded proteins and intracellular vesicle transport, targeting the cell protein synthesis machinery.

CONCLUSIONS: The Vm24 toxin, a highly specific inhibitor of Kv 1.3 channels allowed us to define downstream functions of the Kv 1.3 channels in human CD4+  TEM lymphocytes. Blocking Kv 1.3 channels profoundly affects the mRNA synthesis machinery, the unfolded protein response and the intracellular vesicle transport, impairing the synthesis and secretion of cytokines in response to TCR engagement, underscoring the role of Kv 1.3 channels in regulating TEM lymphocyte function.