Signaling by Ras ^G12V depends on EGFR activity in vivo

Ras proteins are key regulators of signaling pathways initiated by transmembrane tyrosine kinase receptors, and activating Ras mutations are drivers in cancer and RASophaties. The development of effective therapies against these diseases requires a profound understanding of how Ras mutations modify pathway output and interact with other pathway components. In this work 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/Raf/MAPK pathway. We find that Ras ^G12V alters the timing but not the spatial pattern of ERK activation. Consistently, Ras ^G12V mutant proteins respond to EGFR stimulation and can partially compensates for EGFR loss to generate basal levels of ERK activity. However, full pathway activation is still strictly dependent on EGFR function. Altogether, our results suggest that Ras ^G12V mutant proteins act as an amplifier of EGFR stimulation accelerating and raising baseline ERK activity but requiring EGFR signaling for maximal activation. This mechanistic framework supports the use of combined inhibition of both Ras and EGFR to maximize therapeutic efficacy in Ras ^G12V tumors.