SOCS1, SOCS3 and STAT3 expression in melanoma cell lines. (a) Basal expression of SOCS1 and SOCS3 proteins in a panel of n = 10 human melanoma cell lines was measured by immunoblot analysis. β-actin served as a control for equal loading. Basal and IFN-induced SOCS1 and SOCS3 expression was evaluated in (b) human metastatic melanoma cell lines and (c) human embryonic melanocytes (HEM) or vertical (WM793b) and radial (WM1552c) human melanoma cell lines by immunoblot following treatment of human melanoma cell lines with IFN-α (4 hours; 104U/mL) and IFN-γ (4 hours; 10 ng/mL). A375 cells were used as a positive control for SOCS1 and SOCS3 expression (Pos. Ctrl). Immunoblot data shown are representative from at least 3 independent experiments. (d) Constitutive phosphorylation of STAT3 was evaluated in this panel of cell lines by immunoblot analysis. Antibodies directed against STAT3 protein and β-actin were included to control for variations in STAT3 across cell lines and equal loading, respectively.