CELF1 is a non-canonical eIF4E binding protein that promotes translation of epithelial-mesenchymal transition effector mRNAs

Mounting evidence is revealing an increasing complexity of gene regulation at the level of messenger RNA (mRNA) translation. Within mammalian cells, canonical cap-dependent mRNA translation depends on the eIF4F complex, consisting of the m7G mRNA cap-binding protein eukaryotic initiation factor 4E (eIF4E), the helicase eIF4A (eIF4A), and the eIF4G (eIF4G1) scaffolding protein. eIF4G1 additionally binds poly(A) binding protein (PABPC1) to facilitate mRNA circularization and nucleates pre-translation initiation complex assembly to initiate ribosomal scanning. In breast epithelial cells, the CELF1 RNA-binding protein specifically promotes the translation of select epithelial-to-mesenchymal transition (EMT) effector mRNAs by binding GU-rich elements (GREs) within their 3' untranslated regions (UTRs). Here we show that CELF1 directly binds to both eIF4E and PABPC1 to promote eIF4G1-independent translation of GRE-containing mRNAs in mesenchymal cells. Disruption of this CELF1/eIF4E interaction inhibits both EMT induction in vitro and experimental metastasis in vivo. Our findings define a novel, non-canonical mode of translational regulation underlying cellular de-differentiation, raising the possibility that analogous non-canonical modes of translation impact additional transitional cellular states within development and disease.