Western blot analysis for IL-6–induced gp130 phosphorylation in OPM-2 and clone C5 cells before and after ATRA exposure. Cell lysates with equal protein loads from OPM-2 cells (lanes 1 through 4) and clone C5 (lanes 5 through 8) were immunoprecipitated with rabbit anti-human gp130. After SDS-PAGE, immunoblot analysis was done with (a) antiphosphotyrosine (anti-pY) or (b) anti-gp130 antibody and developed by chemiluminescence. Lanes 3, 4, 7, and 8 were from cells pre-treated with ATRA at 10⁻⁶ mol/L for 3 days. Lanes 2, 4, 6, and 8 were from cells stimulated with IL-6 at 100 ng/mL for 10 minutes.