Up-regulation of the IKCa1 Potassium Channel during T-cell Activation

Abstract

We used whole cell recording to evaluate functional expression of the intermediate conductance Ca2ⴙ-acti- vated Kⴙ channel, IKCa1, in response to various mito- genic stimuli. One to two days following engagement of T-cell receptors to trigger both PKC- and Ca2ⴙ-depend- ent events, IKCa1 expression increased from an average of 8 to 300–800 channels/cell. Selective stimulation of the PKC pathway resulted in equivalent up-regulation, whereas a calcium ionophore was relatively ineffective. Enhancement in IKCa1 mRNA levels paralleled the in- creased channel number. The genomic organization of IKCa1, SKCa2, and SKCa3 were defined, and IKCa and SKCa genes were found to have a remarkably similar intron-exon structure. Mitogens enhanced IKCa1 pro- moter activity proportional to the increase in IKCa1 mRNA, suggesting that transcriptional mechanisms un- derlie channel up-regulation. Mutation of motifs for AP1 and Ikaros-2 in the promoter abolished this induction. Selective Kv1.3 inhibitors ShK-Dap22, margatoxin, and correolide suppressed mitogenesis of resting T-cells but not preactivated T-cells with up-regulated IKCa1 chan- nel expression. Selectively blocking IKCa1 channels with clotrimazole or TRAM-34 suppressed mitogenesis of preactivated lymphocytes, whereas resting T-cells were less sensitive. Thus, Kv1.3 channels are essential for activation of quiescent cells, but signaling through the PKC pathway enhances expression of IKCa1 chan- nels that are required for continued proliferation.