MA 06.14 Oncogenic SOS1 Mutations in Lung Adenocarcinoma

Abstract

Lung adenocarcinomas are characterized by genetic alterations along receptor tyrosine kinase pathways. Around 50% of lung adenocarcinomas contain alterations in KRAS and EGFR alone. Nonetheless, genetic drivers in a large proportion of other cases remain to be determined. Recent exome sequencing analysis of lung adenocarcinomas in our lab has identified SOS1, a guanine nucleotide exchange factor, as being significantly mutated in lung cancers lacking canonical oncogenic mutations. However, the functional significance of the mutations is unclear. In vitro cellular assays as well as in vivo transplantation experiments were performed to determine the phenotype of SOS1 mutants. Biochemical approaches were used to determine the mechanism by which SOS1 mutants confer an oncogenic phenotype. RNA sequencing of SOS1 mutant cells was performed to transcriptionally profile the cells, and inhibitors of the RTK/Ras/MAPK pathway were tested for their efficacy against SOS1 mutants. We demonstrate that ectopic expression of mutated SOS1 induces anchorage-independent cell growth in vitro and tumor formation in vivo. Biochemical experiments suggest mutant SOS1 drives over-activation of the Ras pathway, and through RNA sequencing, we identify an upregulation of MYC targets in cells expressing mutant SOS1. Furthermore, we demonstrate that cancer cells with mutant SOS1 are dependent on SOS1 for survival and are also sensitive to inhibitors of the MAPK pathway. Our work provides experimental evidence for the role of SOS1 as a novel oncogene and suggests possible therapeutic mechanisms to target SOS1-mutated cancers.