Suppression of EGFR signaling and drug-induced potentiation are widespread features of oncogenic RTK fusions.

Abstract

Regulation of cancer cells by their environment contributes to tumorigenesis and drug response, though the extent to which the oncogenic state can alter a cell's perception of its environment is not clear. EML4-ALK is a receptor tyrosine kinase (RTK) fusion oncoprotein that suppresses transmembrane EGFR signaling in cancer cells. ALK inhibition restores signaling through EGFR, thereby promoting survival and drug tolerance. Here, we tested whether such modulation of EGFR activity was common among other RTK fusions, which collectively are found in ~5% of all cancers. Using live- and fixed-cell microscopy in isogenic and patient-derived cell lines, we found that a wide variety of RTK fusions suppress transmembrane EGFR, through mechanisms that include the sequestration of the adaptor protein Grb2. Targeted therapies rapidly released Grb2 from sequestration and potentiated EGFR. Synthetic optogenetic analogs of RTK fusions confirmed that cytoplasmic sequestration of Grb2 was sufficient to suppress perception of extracellular EGF and could do so without driving signaling from the synthetic fusion itself, demonstrating that fusion signaling and suppression of EGFR signaling could be functionally decoupled. Our study uncovers that a large number of RTK fusions simultaneously act as both activators and suppressors of signaling, the mechanisms of which could be exploited for biomimetic therapies that enhance cell killing and suppress drug tolerance.