Atypical Exon 2/3 Mutants G48C, Q43K, and E37K Present Oncogenic Phenotypes Distinct from Characterized NRAS Variants

Abstract

NRAS belongs to the RAS family of GTPases. In colorectal cancer (CRC), NRAS mutations are rare compared to KRAS, but may lead to worse outcomes. We report the functional characterization of the novel NRAS mutants—G48C, Q43K, and E37K—identified in Filipino young-onset CRC patients. Unlike previously characterized NRAS mutants with no apparent effects on cell proliferation, these mutants enhanced proliferation of both HCT116 and NIH3T3 cells. This was confirmed in 3D spheroid assays to mimic the spatial organization of cells. G48C and E37K showed apoptosis resistance in both cell lines, and Q43K showed resistance in HCT116 cells. All three showed no effect on cellular migration in NIH3T3, but G48C enhanced the migration rate of HCT116 cells. Actin staining of NIH3T3 cells expressing the mutants showed a shrunken cytoplasm and transient structures associated with motility and invasiveness. Docking simulations show that GDP is only able to bind fully within the binding pocket of wild-type NRAS, but not in the mutants. Further, G48C, Q43K, and E37K all have less negative ΔG values, indicating a weaker GDP-binding affinity compared to wild-type NRAS. Taken together, the results suggest that oncogenic readouts of NRAS mutants are codon- and mutation-specific, with potential repercussions on the aggressiveness, resistance, and therapeutic response.

Keywords

• NRAS
• young-onset colorectal cancer (YO-CRC)
• Ras isoform
• epidermal growth factor receptor