Cause-and-Effect relationship between FGFR1 expression and epithelial-mesenchymal transition in EGFR-mutated non-small cell lung cancer cells

Objectives: Increased FGFR1 expression is associated with resistance to tyrosine kinase inhibitors (TKIs) in EGFR-mutated NSCLC cells and often concomitant with epithelial to mesenchymal transition (EMT). However, the cause-and-effect relationship between increased FGFR1 expression and EMT in the genetic background of EGFR-mutated non-small cell lung cancer (NSCLC) cells is not clear. Previous studies have specifically addressed the relationship between EMT and increased FGFR1 expression in the context of simultaneous TKI-mediated blocking of EGFR-signaling. Here, in the context of EGFR-mutated NSCLC cells with active EGFR-signaling, we have examined whether increased FGFR1 expression drives EMT or is an EMT passenger event. Materials and methods: For cause-and-effect analyses between EMT and FGFR1 expression, including expression of alternative spliced FGFR1 isoforms, we used CRISPR-dCAS9-SAM-mediated induction of the endogenous FGFRI and ZEB1 genes, as well as biochemical EMT-induction, in PC9 and HCC827 NSCLC cell lines harboring activating EGFR-mutations. Results: We find that FGFR1 expression correlates with a ZEB1-associated EMT gene expression profile in NSCLC cells. In experiments using NSCLC cell lines harboring activating EGFR-mutations we show that CRISPR-dCAS9-SAM-mediated induction of FGFRI expression is neither driving an increase in ZEB1 expression nor EMT characteristics. However, CRISPR-dCAS9-SAM-mediated induction of ZEB1 expression drives EMT characteristics and an increase in FGFRI expression. Biochemical induction of EMT also drives an increase in FGFR1 expression. Conclusion From our findings concerning the cause-and-effect relationship in the genetic background of EGFR-mutated NSCLC cells, we conclude that an increase in ZEBI expression is a driver of EMT resulting in concomitant increased FGFRI expression, whereas an increase in FGFRI expression is insufficient to drive concomitant EMT.