Phosphorylation of eIF-4E positively regulates formation of the eIF-4F translation initiation complex following DNA damage

The eukaryotic translation initiation factor 4E (eIF-4E) is essential for cap-dependent protein translation. However, the role of eIF-4E phosphorylation in protein translation is still unclear. In this study, the function of eIF-4E phosphorylation in the formation of the translational initiation complex eIF-4F following DNA damage was investigated. Our results show that etoposide treatment caused a rapid increase in eIF-4E phosphorylation. The addition of CGP57380, a specific inhibitor of the eIF-4E kinase Mnk, not only inhibited eIF-4E phosphorylation but also resulted in reduced interaction between eIF-4E and eIF-4G. Furthermore, neither the p38 MAPK inhibitor nor the ERK inhibitor caused significant inhibition in eIF-4E phosphorylation induced by etoposide. However, a JNK-specific inhibitor, SP600125, strongly suppressed etoposide-induced eIF-4E phosphorylation. Our results provide the first evidence indicating that phosphorylation of eIF-4E by Mnk, possibly mediated by JNK or JNK-like kinases, is critical for formation of the translational initiation complex eIF-4F following DNA damage.