DDX3 Activates CBC-eIF3-Mediated Translation of uORF-Containing Oncogenic mRNAs to Promote Metastasis in HNSCC

Mutated or dysregulated DDX3 participates in the progression and metastasis of cancer via its multiple roles in regulating gene expression and cellular signaling. Here, we show that the high expression levels of DDX3 in head and neck squamous cell carcinoma (HNSCC) correlate with lymph node metastasis and poor prognosis and demonstrate that DDX3 is essential for the proliferation, invasion, and metastasis of oral squamous cell carcinoma (OSCC) cells. Microarray analyses revealed that DDX3 is required for the expression of a set of pro-metastatic genes, including ATF4-modulated genes in an aggressive OSCC cell line. DDX3 activated translation of ATF4 and a set of its downstream targets, all of which contain upstream open reading frames (uORF). DDX3 promoted translation of these targets, likely by skipping the inhibitory uORF. DDX3 specifically enhanced the association of the cap-binding complex (CBC) with uORF-containing mRNAs and facilitated recruitment of the eukaryotic initiation factor 3 (eIF3). CBC and certain eIF3 subunits contributed to the expression of metastatic-related gene expression. Taken together, our results indicate a role for the novel DDX3-CBC-eIF3 translational complex in promoting metastasis. Significance: The discovery of DDX3-mediated expression of oncogenic uORF-containing genes expands knowledge on translational control mechanisms and provides potential targets for cancer therapy. [GRAPHICS] . (C) 2018 AACR.