eIF3a-PPP2R5A-mediated ATM/ATR dephosphorylation is essential for irinotecan-induced DNA damage response

Objectives The individual differences and pervasive resistance seriously hinder the optimization of irinotecan-based therapeutic effectiveness. Eukaryotic translation initiation factor 3a (eIF3a) plays a key role in tumour occurrence, prognosis and therapeutic response. This study focused on the role of eIF3a in irinotecan-induced DNA damage response. Materials and Methods The cck8 cell viability and clone survival analyses were used to test the regulatory role of eIF3a on irinotecan sensitivity in HT29 and CACO2 cell lines in vitro. This regulatory role was also verified in vivo by conducting subcutaneous xenograft model. Irinotecan-induced DNA damage, cell cycle arrest and apoptosis were tested by flow cytometry analysis, TUNEL staining, western blot and comet assays. The immunofluorescence, co-IP, luciferase reporter assay, RIP and flow cytometric analyses were carried out to investigate the underline mechanism. Results We demonstrated that eIF3a continuously activates ATM/ATR signal by translationally inhibiting PPP2R5A, a phosphatase that directly dephosphorylates and inactivates ATM/ATR after DNA repair complete. Suppression of PPP2R5A resulted in chronic ATM/ATR phosphorylation and activation, impairing DNA repair and enhancing irinotecan sensitivity. Conclusions Our study suggested eIF3a with a high potential to influence phenotypic functions, which may contribute substantially to the early identification of susceptible individuals and the provision of personalized medication to irinotecan-treated patients.

Automated summary

Our study demonstrates that eIF3a continuously activates the ATM/ATR signaling pathway by inhibiting the translation of PPP2R5A, leading to chronic phosphorylation and activation of ATM/ATR. This impairs DNA repair and enhances the sensitivity to irinotecan.