Analysis of cyclin-dependent kinase 2-regulated phosphorylation of stathmin in etoposide-induced apoptotic HeLa cells by two-dimensional electrophoresis and mass spectrometry

Abstract

The candidate proteins that are involved in the cyclin-dependent kinase 2 (cdk2) signaling pathway were analyzed by comparing different proteins between dominant negative cdk2 overexpressed and control HeLa cells using two-dimensional electrophoresis (2-DE) and mass spectrometry (MS). The 2-DE and MS indicated that stathmin and its monophosphorylated form were induced in etoposide-treated HeLa cells compared to untreated cells and this effect was inhibited by overexpression of dominant negative mutant form of cdk2. Further analysis showed that serine-25 (Ser-25), which comprises the conserved target motif for phosphorylation by mitogen-activated protein kinase (MAPK), was the major phosphorylation site of monophosphorylated form of stathmin. These findings indicate that etoposide-induced expression and phosphorylation at Ser-25 of stathmin might be mediated by activation of the MAPK signaling pathway, which is mediated by the cdk2 activation during the onset of the anticancer agent induced apoptotic events in the cancer cells.