Up-regulation of the IKCa1 potassium channel during T-cell activation - Molecular mechanism and functional consequences

We used whole cell recording to evaluate functional expression of the inter mediate conductance Ca2+-activated KC channel, IKCa1, in response to variou s mitogenic stimuli. One to two days following engagement of T-cell recepto rs to trigger both PKC- and Ca2+-dependent events, IKCa1 expression increas ed from an average of 8 to 300-800 channels/cell. Selective stimulation of the PKC pathway resulted in equivalent up-regulation, whereas a calcium ion ophore was relatively ineffective. Enhancement in IKCa1 mRNA levels paralle led the increased channel number. The genomic organization of IKCa1, SKCa2, and SRCa3 were defined, and IKCa and SKCa genes were found to have a remar kably similar intron-exon structure, Mitogens enhanced IKCa1 promoter activ ity proportional to the increase in IKCa1 mRNA suggesting that transcriptio nal mechanisms underlie channel up-regulation. Mutation of motifs for AP1 a nd Ikaros-2 in the promoter abolished this induction. Selective Kv1.3 inhib itors ShK-Dap(22), margatoxin, and correolide suppressed mitogenesis of res ting T-cells but not preactivated T-cells with up-regulated IKCa1 channel e xpression. Selectively blocking IKCa1 channels with clotrimazole or TRAM-34 suppressed mitogenesis of preactivated lymphocytes, whereas resting T-cell s were less sensitive. Thus, Kv1.3 channels are essential for activation of quiescent cells, but signaling through the PKC pathway enhances expression of IKCa1 channels that are required for continued proliferation.