Effect of wt SOCS-1 transfection on MedB-1 cells. (A) MedB-1 cell proliferation assay. The cell densities at the beginning of the experiments were adjusted to 1 × 10⁵ cells/mL. Cell numbers were determined in triplicates every day in 50 μL cell suspension from MedB-1 cells cultured in complete medium (○), in medium supplemented with 20 μM Tyrphostin AG490 (), and in MedB-1 cells transfected with wt SOCS-1 plasmid (•) and mock plasmid (▪). (B) Western blot analysis of wt SOCS-1–transfected MedB-1 cells. Twenty-four hours after transfection with a mock plasmid (lane 1) and the wt SOCS-1 plasmid (lane 2), proteins were extracted and subjected to Western blot analyses as described; β-actin is shown as loading control. While the content of JAK2 and STAT5 proteins is at comparable levels, phosphorylation is barely detectable in transfectants.