Characterizing the interaction of the mammalian eIF4E‐related protein 4EHP with 4E‐BP1

Eukaryotic initiation factor 4E‐binding protein 1 (4E‐BP1) represses translation initiation by binding to eukaryotic initiation factor 4E (eIF4E). 4E‐BP1 also binds to the eIF4E homologous protein (4EHP). We show that eIF4E‐binding mutants of 4E‐BP1 (Y54A and L59A) fail to form heterodimeric complexes with wild‐type 4EHP. In addition, the W95A mutant of 4EHP, similar to a homologous mutation in eIF4E, inhibits its binding to wild‐type 4E‐BP1. Interestingly, 4EHP over‐expression instigates a negative feedback loop that inhibits upstream signaling to 4E‐BP1 and ribosomal protein S6 kinase 1 (S6K1) whereas the 4E‐BP1‐binding‐deficient mutant of 4EHP(W95A) was unable to trigger this feedback loop. Thus, the interaction of 4EHP with 4E‐BP1 is necessary for this observed impaired signaling to 4E‐BP1 and S6K1.