Signaling by RasG12V requires EGFR function in vivo to trigger full downstream pathway activation

Ras proteins regulate signaling pathways initiated by tyrosine kinase receptors, and activating Ras mutations are drivers in cancer and RASophaties. The development of therapies against these diseases requires a profound understanding of how Ras mutations modify pathway output and interact with other pathway components. Here we generated G12V activating mutations in the Drosophila Ras1 locus and used Ras1 G12V and human KRASB G12V to analyze in vivo the consequences of endogenous Ras G12V expression and its interplay with other components of the EGFR/MAPK pathway. We find that Ras G12V acts as an amplifier of EGFR stimulation. Consistently, Ras G12V proteins respond to EGFR and can compensate for EGFR loss to generate basal levels of ERK activity. However, full pathway activation by Ras G12V is strictly dependent on EGFR function. Altogether, our results suggest that EGFR not only activates wild type Ras, but also Ras G12V , and support the notion that Ras G12V mutants are non-constitutively active.