Stathmin dynamics modulate the activity of eribulin in breast cancer cells

Stathmin, a phosphoprotein that modulates microtubule dynamics, is highly expressed in breast cancer cells. Eribulin, a microtubule‐depolymerizing agent, is used to treat patients with advanced breast cancer. However, the detailed mechanisms underlying the action of eribulin during microtubule catastrophe, and the interaction between eribulin and stathmin dynamics, remain unclear. Here, we investigated the role of stathmin in the antiproliferative activity of eribulin in breast cancer cells. Eribulin induced phosphorylation of stathmin in MCF7 and MDA‐MB‐231 cells; this was attenuated by an inhibitor of protein kinase A (H89) and an inhibitor of Ca(2+)/calmodulin‐dependent kinase II (KN62). In addition, expression of phosphorylated stathmin was reduced by the protein phosphatase PP2A activator FTY720 but increased by the PP2A inhibitor okadaic acid. Of note, expression of PP2A subunits in eribulin‐treated cells decreased, although eribulin did not affect the phosphatase activity of recombinant PP2A directly. Furthermore, the antiproliferative effect of eribulin was stronger in stathmin‐overexpressing cells. These results suggest that stathmin dynamics are closely associated with the antiproliferative effects of eribulin and stathmin is a possible biomarker for predicting the therapeutic effects of eribulin in breast cancer patients.