Therefore, we conclude that bortezomib-induced phosphorylation of stathmin promotes cell death and that phosphorylation on Ser16, Ser25 and Ser38 is necessary for this process. Furthermore, the bortezomib-induced changes in the MT stabilization can be attributed to the bortezomib-induced phosphorylation of stathmin, and MT stabilization is in fact responsible for the bortezomibinduced cell death-promoting activity of phosphorylated stathmin.