TGF-β-mediated phosphorylation of hnRNP E1 induces EMT via transcript-selective translational induction of Dab2 and ILEI

Abstract

TGFβ induces epithelial-mesenchymal transdifferentiation (EMT) accompanied by cellular differentiation and migration. Despite extensive transcriptomic profiling, identification of TGFβ-inducible, EMT-specific genes has met with limited success. Here, we identify a post-transcriptional pathway by which TGFβ modulates expression of EMT-specific proteins, and EMT itself. We show that heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1) binds a structural, 33 nucleotides (nt) TGF beta-activated translation (BAT) element in the 3’-UTR of disabled-2 (Dab2) and interleukin-like EMT inducer (ILEI) transcripts, and repress their translation. TGFβ activation leads to phosphorylation at Ser43 of hnRNP E1 by protein kinase Bβ/Akt2, inducing its release from the BAT element and translational activation of Dab2 and ILEI mRNAs. Modulation of hnRNP E1 expression or its post-translational modification alters TGFβ-mediated reversal of translational silencing of the target transcripts and EMT. These results suggest the existence of a TGFβ-inducible post-transcriptional regulon that controls EMT during development and metastatic progression of tumors.