IRF4 is overexpressed in ATL and bound to transcriptional target genes.
A, Western blotting demonstrating IRF4 expression in CD3/CD28-activated PBMCs and Jurkat, MT2, MT4, TL-OM1, MT1, and ED40515 cell lines. An immunoblot shows Tax protein expression. Env-Tax fusion protein in lane 3 of the Tax blot (middle) is seen between 50 and 75 kDa and indicated by the top arrow. Tax-specific bands are seen in lanes 3 and 4 of the Tax blot at 40 kDa, as indicated by the bottom arrow. Immunoblot for actin (bottom) shows actin expression as loading control. B–F, binding of IRF4 to HELIOS 3′-regulatory region (B), CTLA4 gene (C), IFNβ gene (D), cFLIP gene (E), and a control genomic region 10 kilobases upstream of the IRF4 start site (F) by IRF4, as demonstrated by a ChIP assay in CD3/CD28-activated PBMCs and Jurkat, MT2, MT4, TL-OM1, and MT1 cells. B–F, results of four replicates. Error bars, S.E. *, p < 0.05; **, p < 0.01; ***, p < 0.001.