Comparative kinase expression analysis across different cancer cell lines. A, scheme illustrating the SILAC-based chemical proteomics workflow for quantitative comparison of VI16832-interacting sub-proteomes in three cancer cell lines. B, quantified ratios for protein kinases and other nucleotide-binding proteins were transformed into relative expression levels with the highest expression in any of the three cell lines set to 1. Based on these values, a heat map was generated to visualize relative expression levels across the analyzed cancer cell lines. C, summed relative expression values for the seven major kinase groups as well as the atypical and other kinases according to Manning et al. (2) were compared for MV4–11, HCT116, and 435S cells. In addition, members of the tyrosine kinase (TK) group were subdivided into cytoplasmic and receptor tyrosine kinase in the cell line comparison. D, total cell lysates of MV4–11, HCT116, and 435S cells were immunoblotted with antibodies recognizing the kinases Axl, DDR1, FAK, Fer, Fes, JAK1, Met, PAK4, PYK2, and Syk. For comparison, binding ratios according to the SILAC-based quantification of VI16832 resin-bound protein kinases are shown.