Mutations and Targeted Drugs Alter RAS Signaling Dynamics in Cancer

Multiple signaling transduction pathways converge to form complex networks that drive essential cellular processes. Oncogenic mutations have been shown to drive aberrant activation of crucial signal transduction pathways, but it is unclear whether these mutations affect the kinetics of pathway activation. Recently, optogenetic methods in which light inputs are used to selectively activate intracellular signaling nodes have developed to separately characterize the effect of a specific node on a shared node. To further elucidate the role of oncogenic mutations and targeted drugs on the dynamics of RAS–ERK signaling, Bugaj and colleagues performed live-cell or high-throughput fluorescence microscopy to assess the effect of optogenetic stimulation of RAS on ERK output in normal lung epithelial, patient-derived non–small cell lung cancer (NSCLC), and NIH3T3 cell lines. Compared to NIH 3T3 cells, the NSCLC cell line H1395, which harbored a mutation in the P-loop of BRAF that enhances BRAF dimerization, exhibited a delay in both activation and deactivation of ERK in response to optogenetic RAS stimulation. H1395 cells were less responsive than normal lung epithelial cells or NSCLC cells harboring the BRAF kinase domain mutation BRAF^V600E to high-frequency RAS stimulation due to the slow ERK pathway kinetics. Consistent with these findings, NSCLC cell lines harboring BRAF P-loop mutations exhibited slow ERK activation in response to optogenetic stimulation of RAS, and treatment with paradox-activating BRAF dimerization-promoting drugs prolonged ERK kinetics in normal cells. Slowed pathway kinetics induced by BRAF paradox inhibitors drove altered expression of ERK target genes in response to pulsed RAS stimulation, and these expression changes promoted cell-cycle entry compared to cells with normal, fast ERK pathway kinetics. Together, these results elucidate the role of cancer mutations and targeted drugs in altering cellular signaling dynamics and suggest that characterization of signaling kinetics in cancer cells may provide insight into cancer biology and therapeutic strategies.

Bugaj LJ, Sabnis AJ, Mitchell A, Garbarino JE, Toettcher JE, Bivona TG, et al. Cancer mutations and targeted drugs can disrupt dynamic signal encoding by the Ras-Erk pathway. Science 2018;361:eaao3048.

• ©2018 American Association for Cancer Research.