Inhibition of Interleukin 10 Transcription through the SMAD2/3 Signaling Pathway by Ca2+-Activated K+ Channel KCa3.1 Activation in Human T-Cell Lymphoma HuT-78 Cells

The hyperpolarization induced by intermediate-conductance CA²⁺-activated K⁺ channel (K_CA3.1) activation increases the driving force for CA²⁺ influx, which generally promotes cell proliferation, migration, and cytokine production in immunocompetent cells. Interleukin-10 (IL-10) from tumor-infiltrating lymphocytes and macrophages, lymphoma, and carcinoma cells facilitates escape from Cancer immune surveillance; however, the role of K_CA3.1 in IL-10 production remains unclear. The objective of the present study was to elucidate the involvement of K_CA3.1 in IL-10 expression and production using the human T-cell lymphoma HuT-78 cells. In HuT-78 cells, IL-10 gene expression and production were reduced by treatment with the K_CA3.1 activator, as 6-hour Western blotting showed that the protein expression ratio of phosphorylated SMAD2 (P-Smad2)/SMAD2, but not P-Smad3/SMAD3, was decreased by the treatment with K_CA3.1 activator in HuT-78 cells. Concomitant with this, the nuclear translocation of P-Smad2 was inhibited by K_CA3.1 activator. Furthermore, the K_CA3.1 activator-induced transcriptional repression of IL-10 disappeared with pretreatment with the Calmodulin kinase II (CaMKII) inhibitor KN-62 for 1 hour, and K_CA3.1 activator-induced decreases in the nuclear translocation of P-Smad2 were also prevented by pretreatment with KN-62. Taken together, the K_CA3.1 activator-induced transcriptional repression of IL-10 is due to the inhibition of the nuclear translocation of P-Smad2 in HuT-78 cells, resulting in the prevention of P-Smad2/3 complex formation in nuclei, and the activation of CaMKII induced by K_CA3.1 activators suppresses the constitutive activation of P-Smad2/3 in HuT-78 cells. Therefore, K_CA3.1 activators have potential as a therapeutic option to suppress the tumor-promoting activities of IL-10.