eIF3 targets cell proliferation mRNAs for translational activation or repression

Regulation of protein synthesis is fundamental for all aspects of eukaryotic biology by controlling development, homeostasis, and stress responses(1,2). The 13-subunit, 800-kDa eukaryotic initiation factor 3 (eIF3) organizes initiation factor and ribosome interactions required for productive translation(3). However, current understanding of eIF3 function does not explain genetic evidence correlating eIF3 deregulation with tissue-specific cancers and developmental defects(4). Here we report the genome-wide discovery of human transcripts that interact with eIF3 using photo-activatable crosslinking and immunoprecipitation (PAR-CLIP)(5). eIF3 binds to a highly specific programme of messenger RNAs (mRNAs) involved in cell growth control processes, including cell cycling, differentiation, and apoptosis, via the mRNA 5′ untranslated region (5′ UTR). Surprisingly, functional analysis of the interaction between eIF3 and two mRNAs encoding cell proliferation regulators, c-Jun and BTG1, reveals that eIF3 employs different modes of RNA stem loop binding to exert either translational activation or repression. Our findings illuminate a new role for eIF3 in governing a specialized repertoire of gene expression and suggest that binding of eIF3 to specific mRNAs could be targeted to control carcinogenesis.