Paclitaxel induces the phosphorylation of the eukaryotic translation initiation factor 4E-binding protein 1 through a Cdk1-dependent mechanism

Initial chemotherapeutic treatment triggers a stress-related response, which can lead to an increase in the expression of survival proteins. In this study we examine whether paclitaxel (PTX) alters the expression and/ or phosphorylation of the translation initiation proteins, eukaryotic initiation factor 4E (eIF-4E) and 4E-binding protein (4E-BP1), a suppressor of eIF-4E in the dephosphorylated state. We found that PTX induced the hyperphosphorylation of 4E-BP1 in the breast cancer cell line, MDA MB 231, which reduced its association with eIF-4E, but did not alter the expression and phosphorylation of eIF-4E. The hyperphosphorylation of 4E-BP1 correlated with G2/M accumulation and with an increase in the phosphorylation of cdk1 substrates. Cotreatment with a histone deacetylase inhibitor (an indirect inhibitor of cdk activity), purvalanol A and roscovitine (direct cdk inhibitors), and the reduction of cyclin B expression using RNA interference decreased the hyperphosphorylation of 4E-BP1 in PTX treated cells. The hyperphosphorylation of 4E-BP1 by PTX increased the association of eIF- 4E with eIF-4G, whereas cotreatment with purvalanol A inhibited the association of eIF-4E with eIF-4G in PTX treated cells. Taken together, our data suggest that PTX-increases the functional level of eIF-4E by promoting the hyperphosphorylation and release of 4E-BP1 through a cdk1-dependent mechanism.