mRNA Translation Regulation is Mediated by Multiple 5' UTR and Start Codon Features.

Regulation of mRNA translation by eukaryotic initiation factors (eIFs) is crucial for cell survival. In humans, eIF3 stimulates translation of the mRNA which encodes the transcription factor JUN, an oncogenic transcription factor involved in cell cycle progression, apoptosis, and cell proliferation. Previous studies revealed that eIF3 activates translation of the mRNA by interacting with a stem loop in the 5' untranslated region (5' UTR) and with the 5'-7-methylguanosine cap structure. In addition to its interaction site with eIF3, the 5' UTR is nearly one kilobase in length, and has a high degree of secondary structure, high GC content, and an upstream start codon (uAUG). This motivated us to explore the complexity of mRNA translation regulation in human cells. Here we find that JUN translation is regulated in a sequence and structure-dependent manner in regions adjacent to the eIF3-interacting site in the 5' UTR. Furthermore, we identify contributions of an additional initiation factor, eIF4A, in regulation. We show that enhancing the interaction of eIF4A with by using the compound Rocaglamide A (RocA) represses translation. We also find that both the upstream AUG (uAUG) and the main AUG (mAUG) contribute to translation and that they are conserved throughout vertebrates. Our results reveal additional layers of regulation for translation and show the potential of as a model transcript for understanding multiple interacting modes of translation regulation.