STAT3 is constitutively activated in HD cell lines but not in BL cells lines.

Equal amounts of nuclear extracts of each cell line (as indicated) were analyzed in a gel retardation experiment using radiolabeled oligonucleotides containing the consensus or a mutated STAT1/3 binding site as described in “Material and methods.” HepG2 cells were stimulated with IL-6 (15 minutes, 250 U) before nuclear extracts were prepared. The position of STAT3 and STAT1 homodimers and heterodimers are shown by arrows.