Proliferation assay in the C33 cell line expressing VWT and VGly proteins of mumps virus. Proliferation was measured with CellTiter 96 Aqueous One Solution Cell Proliferation Assay (Promega). Cells were treated 12 h with IFN-α, 12 h with MG132 and 2 h with PD98059. The absorbance (490 nm) was measured in a Shimadzu spectrophotometer, 4 h after addition of MTS. Each column represents the mean ± SD of three independent experiments. *, statistical difference between treatment groups and the control group. §, statistical difference between samples with and without treatment. ℓ, statistical difference between the samples treated with PD98059 and triple therapy with respect to samples treated with IFN/MG132. Each column represents the mean ± SD of three independent experiments. Student t-test (P < 0.05).