The three RAS genes (KRAS, NRAS, and HRAS) encode four highly identical (~90% sequence identity) proto- oncogenes. Together they represent the most commonly mutated oncogene family in human cancers, mutated in ~25% of all cancers. However, the mutational frequency of each RAS gene is unique among different cancer types. Mutations in KRAS are most prevalent in pancreatic cancer (97% KRAS, 0% NRAS, 0% HRAS), whereas NRAS is predominantly mutated in melanoma (1%, 28%, 1%, respectively), and HRAS in bladder cancer (3%, 1%, 6%, respectively). This suggests that each RAS gene drives biological differences within various cancer types. Additionally, recent studies have reported that the non-mutated, wild type (WT) counterparts in mutant (MT) RAS-driven cancers can have tumor driver activities. These findings are confounding, because in the context of MT RAS-driven cancers, WT RAS proteins are largely considered ?inactive?. These observations suggest that the WT and MT RAS proteins either play distinct roles or simply have additive activities. I propose to test the roles of the WT and mutated RAS proteins in human lung adenocarcinoma (LAC) cell lines, the leading cause of cancer deaths, where mutations in RAS proteins account for 32% of all cases. I will use cell lines that are both MT KRAS (mutated in 31% of LAC) and MT NRAS (mutated in 1% of LAC) driven. I hypothesize that the different mutational frequencies between the KRAS and NRAS isoforms will be based on different biological activities in LAC. Furthermore, I expect to identify unique mechanisms that correlate with specific WT and MT RAS isoforms and contribute to oncogenesis. My preliminary data show that the suppression of both WT and MT RAS isoforms inhibits the growth of LAC cancer cells and imparts differential signaling through downstream effectors. I propose three aims to investigate the roles of WT and MT RAS isoforms in LAC.
In aim 1, I will determine if WT and MT RAS isoforms impact the growth of LAC cells in vitro using both 2D and 3D models, and in vivo within subcutaneous xenografts.
In aim 2, I will define the metabolic dependencies of each RAS isoform, namely their impact on autophagic flux, macropinocytosis, mitochondrial function, glycolysis and respiration. Finally, in aim 3, I will identify compensatory mechanisms that allow cells to overcome their addiction to WT and MT RAS. These studies will provide key mechanistic insights as to how MT and WT RAS signaling works in concert to drive oncogenesis in LAC. Thus, these studies will address important issues within the RAS field.
The three RAS genes, KRAS, NRAS, and HRAS, are the most commonly mutated family of genes in human cancers (25%). Although each cancer cell expresses all three corresponding RAS proteins, only one isoform is ever mutated, and mutations of each protein is found in disparate frequencies across cancer types, suggesting each isoform plays distinct biological roles. In this proposal, I will investigate the roles of all three RAS proteins in mutant KRAS- and NRAS-driven lung cancer by determining their contribution towards growth, proliferative signaling pathways, metabolic processes, and define mechanisms of resistance that can compensate for their loss.
