Figure 4.

Ubiquitin specific peptidase 4 (USP4) and interferon regulatory factor 4 (IRF4) synergize with nuclear factor of activated T cell-2 (NFATc2) to specifically enhance NFAT-mediated activation of the interleukin-4 (IL-4) promoter. (A) Cotransfection with USP4 and IRF4 had no significant effects on the luciferase activity of IL-4-luc. (B and C) Cotransfection with USP4, IRF4 and NFATc2 markedly increased the luciferase activity of IL-4-luc compared with that of the controls. ^*p<0.05 and ^**p<0.01. (D) The expression levels of IL-4 and IRF4 were decreased by the treatment of vialinin A. Naïve CD4⁺ T cells were sorted using flow cytometry-based analysis and were cultured for Th2 cell differentiation, and were treated with the inhibitor of USP4, vialinin A, for 12 h. Th2 cells were then treated with phorbol myristate acetate (PMA, 25 ng/ml) and ionomycin (1 µg/ml) for 4 h and processed by flow cytometry.