MePDN inhibits both natural cytotoxicity and the cytokine-induced ERK phosphorylation. (A) NK cells were cultured for 5 days with IL-2 or IL-15 in the presence or absence (control = CTR) of MePDN concentrations ranging from 0.5 to 0.01 μg/mL (MePDN 0.5, MePDN 0.1, MePDN 0.01). A 4-hour 51Cr-release assay was performed in order to assess the cytolytic activity against the human HLA class I–negative, the 721-221 B-EBV (▪), or FO1 melanoma cell lines (⊡). The effector-target (E/T) ratio was 5:1. Data are expressed as percentage of target-cell lysis. This is representative of 8 experiments performed. (B) NK cells derived from the same donors were stimulated overnight with IL-2 (100 U/mL) or IL-15 (20 ng/mL) in the presence or absence (control = CTR) of different MePDN concentrations from 1 to 0.01 μg/mL (MePDN 1, MePDN 0.5, MePDN 0.1, MePDN 0.01). Total-cell lysates were analyzed by WB using antihuman antibody against p-ERK1/2 and membranes were probed again with antibody recognizing the native protein in order to assess comparable amounts of proteins. In this figure, a representative experiment of 6 performed is shown.
