Electrophoretic mobility shift assay. Nuclear extracts prepared from E4 TEPC clone were incubated in the presence of the 5′ end-labeled IRF-1 probe and electrophoresed on a 6% polyacrylamide gel. The bound IRF-1 complexes (C1, C2, and C3) and the supershifted IRF-1 complexes (S1 and S3) are indicated. Extract from noninduced (lane 1), IL-6–induced (lanes 2 through 5), or Epo-induced (lanes 6 through 9) cells were incubated with antibodies specific for Stat1 (lanes 3 and 7), Stat3 (lanes 4 and 8), and Stat5 (lanes 5 and 9) or without antiserum (lanes 2 and 6).