Inhibition of Interleukin 10 Transcription through the SMAD2/3 Signaling Pathway by Ca²⁺-Activated K⁺ Channel K_Ca3.1 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.

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