GSE113695
EIF1AX-A113 splice and RAS mutations cooperate to drive thyroid tumorigenesis through ATF4 and c-MYC
Translation initiation in higher eukaryotes is orchestrated by the tight regulation of the cap binding and the 43S pre-initiation complexes (PIC). The PIC component eukaryotic initiation factor 1A (EIF1A), encoded on human chromosomes X and Y by EIF1AX and EIF1AY, respectively, is essential for recruitment of the ternary complex and for assembling the 43S PIC, which after recruitment onto capped mRNAs scans their 5'UTR and localizes the AUG to initiate translation. Recurrent EIF1AX mutations are found in several cancers, including ~1% of papillary thyroid cancers in a mutually exclusive manner with other drivers (BRAF, RAS, and oncogenic fusions). They are enriched in advanced thyroid cancers (11%) where they display a striking co-occurrence with RAS, which we show cooperate to induce tumorigenesis in mouse models and in isogenic cell lines. The C-terminal tail EIF1AX-A113splice mutation is the most prevalent in advanced thyroid cancer, and private to this disease. We found that EIF1AX-A113spl variants stabilize the PIC and induces ATF4 expression, a sensor of cellular stress, which is co-opted to suppress EIF-2a phosphorylation, thus enabling a general increase in protein synthetic rate. RAS stabilizes c-MYC, an effect augmented by EIF1AX-A113spl. ATF4 and c-MYC induce expression of aminoacid transporters, and enhance sensitivity of mTOR to aminoacid supply. These mutually reinforcing events generate therapeutic vulnerabilities to MEK, BRD4 and mTOR kinase inhibitors. The RNA-Seq and Ribosome Profiling samples provided here were used to support the claim of increased translational efficiency of ATF4. Overall design: Comparison of Ribosome footprints in the context of EIF1AX-splice mutated (C643) and splice reverted isogenic cell line (C643-spl- rev), three replicates of ribosome-protected RNA sequencing and three replicates of RNA-seq were used. Additionally, 3 replicates of RNA-seq comparing KRAS G12R mutant CAL62 vs. CAL62-splice, an isogenic cell line generated with CRISPR-Cas9 mediated knock in of EIF1AX-splice mutation.