IRF4 is highly expressed and drives Myc expression and proliferation in PTCL cell lines. (A) IRF4 expression was absent in normal resting T cells and was induced upon stimulation with PMA/ionomycin (PMA/I). This induction was blocked by the PKCĪ² inhibitor LY317615 (enzastaurin). PTCL cells constitutively expressed IRF4, and this expression was resistant to inhibition by LY317615. (B) siRNA-based knockdown of IRF4 inhibited cell proliferation (25 nM siRNA, P < .0001; 50 nM siRNA, P < .0001) in Karpas 299 (B); IRF4 (P = .0009) and MYC (P = .0048) gene expression in Karpas 299 (C); and IRF4 and MYC protein expression in Karpas 299 (D). (E) ChIP for IRF4 demonstrated binding to the MYC promoter in Karpas 299 cells. (F) Overexpression of IRF4 increased MYC promoter activity in Karpas 299 (luciferase assay, P = .0032). (G) MYC knockdown did not inhibit IRF4 gene expression (P = .91) (G), and had only minimal effect on IRF4 protein expression in Karpas 299 (H).
