In particular, as suggested by protein network analysis (Fig. 3B) , stathmin may play a central role in mediating bortezomib-induced apoptosis in MM cells. Stathmin (also termed as p19, 19K, p18, prosolin, and Op18) is a ubiquitous 19 kDa cytosolic phosphoprotein that is highly expressed in a wide variety of cancers, including a subset of leukemias and breast carcinomas and is a key regulator in the control of proliferation and cell cycle [32, 33] . Stathmin is a phosphorylation responsive regulator of microtubule (MT) dynamics that increases the catastrophe rate of MTs (depolymerization or shrinkage phase of individual MTs) in a dose-dependent manner [34] . Four Ser residues, Ser16, Ser25, Ser38, and Ser63 in stathmin are subjects for phosphorylation in intact cells [26] .