Protective concentrations of IL-6 do not activate ERK function. 8226, AF-10, and UCLA #1 MM cells cultured with and without IL-6 (1,000 U/mL, upper panel) or with and without PMA (500 nmol/L, lower panel). Whole-cell lysates were then tested for enzymatic activity against the substrate MBP in an in vitro kinase assay.