TITLE
Biochemical properties and implications of NRAS mutant-specific BRAF interactions in melanoma
ABSTRACT
Extracellular growth factors promote cellular proliferation, motility, and survival through a complex network of
signal transduction pathways. Thus, mutations in these pathways can cause inappropriate cellular proliferation
and lead to diseases, such as cancer. RAS, an intracellular hub for multiple signaling pathways, is mutated in
20-30% of all human cancers. While the three RAS isoforms (H-, K-, and N-RAS) share a high degree of
similarity, each RAS-driven cancer type is enriched for mutations in a specific RAS isoform, codon (12, 13, or
61), and amino acid. We do not fully understand the mechanism driving this observed selectivity, although each
RAS mutant has distinct biochemical and functional properties. Elucidating the mechanisms underlying these
mutational preferences could help identify the features of oncogenic RAS required to initiate cancer in different
tissue types.
To address this knowledge gap, we have focused on the selection of specific NRAS mutants in melanoma. Our
work has shown that common melanoma-associated NRAS mutants (Q61R, K) promote MAPK signaling through
increased activation of BRAF homo- and hetero-dimers. New molecular dynamics simulations suggest that
conformational properties, specific to the NRAS mutants that drive melanoma, facilitate BRAF binding. Here, I
will test the hypothesis that structural differences between NRAS mutants determine their ability to
outcompete autoinhibitory BRAF interactions, drive enhanced MAPK>ERK activation, and alter the
potency of RAF inhibitors. To test my hypothesis, I will use a variety of in vitro biosensors, cell-based signaling
assays, and mouse models to define the mutant-specific features of NRAS that facilitate BRAF interactions (Aim
1) and how the structural determinants of different NRAS mutant-BRAF interactions influence BRAF inhibitor
sensitivity (Aim 2). Successful completion of these studies will enhance my knowledge of structural biology,
therapeutic development, and mouse models of cancer. I will also identify mutant-specific NRAS-BRAF
interfaces to guide the design of novel therapeutic approaches for NRAS-mutant cancers and provide information
relevant to the clinical implementation of next-generation RAF inhibitors.