Activation of STAT3 in HD cell lines is not enhanced by IL-6.

The cell lines L540 (lanes 1-4) and L1236 (lanes 5-8) were cultured as described in “Materials and methods.” The cells were washed twice with serum-free medium and incubated with serum-containing medium (lanes 1 and 5), in 0.5% BSA-containing medium (lanes 2 and 6), in 0.5% BSA-containing medium with 250 U/mL IL-6 (lanes 3 and 7), or in 0.5% BSA-containing medium with 250 U/mL IL-6 and 1 μg/mL soluble recombinant IL-6R (lanes 4 and 8) for 30 minutes. Nuclear extracts (5 μg) of each cell line were analyzed in a gel retardation experiment using radiolabeled oligonucleotides containing the consensus STAT1 and STAT3 binding sites as described in the legend to Figure 1. Arrows indicate the position of STAT3 and STAT1 homodimers and heterodimers.