To further confirm the results from the quantitative phosphoproteome analysis, we chose stathmin for Western blotting verification using an anti-phospho-Ser38 stathmin antibody. As shown in Figure 2C , SILAC results were very much consistent with Western blotting analysis for this protein. Upon bortezomib treatment, phosphorylation of stathmin at Ser38 increased, whereas steady-state stathmin remained almost unchanged in Western blotting verification.