IFN-λ1 mediated cell growth of multiple myeloma cells is Erk dependent. (a) Phosphorylated and total Erk levels were determined by western blot after stimulation of KAS-6/1 cells with 0.1 μg/ml IFN-λ1, 10 000 U/ml IFN-α, 0.1 μg/ml IL-10, 0.05 μg/ml IL-6, 0.1 μg/ml IGF-1 or 25 ng/ml PMA. The fold increase in phosphorylated Erk was calculated as described in Materials and methods and it is shown below the upper panel. (b) KAS-6/1 cells were cultured in the presence of 0.5 μg/ml IFN-λ1, 4000 U/ml IFN-α or 0.1 μg/ml IL-10 alone or with 50 μM PD98059 for 3 days. Values represent the mean of triplicate values of a representative experiment (n = 5). IGF-1, Insulin-like growth factor-1; IFN, Interferon; IL, interleukin.