Effects of Dex and/or IL-6 on CDK2, CDK4, and CDK6 protein kinase activities. OCI-My5 MM cells were cultured with media alone, IL-6 (50 ng/mL), Dex (1 μmol/L), or Dex (1 μmol/L) and IL-6 (50 ng/mL). Total lysates were prepared 16 hours later and immunoprecipitated with anti-CDK2, anti-CDK4, or anti-CDK6 polyclonal Abs. Histone H1 or GST-RB fusion protein was used as substrate for kinase activity assays of CDK2 immune complex or of CDK4 and CDK6 immune complexes, respectively. The intensity was quantitated with densitometry and relative kinase activities of CDK2 (▪), CDK4 (▨), and CDK6 () compared in cells cultured in media, IL-6, Dex, or both IL-6 and Dex.