Glucose deprivation selects for KRAS and BRAF mutations in colorectal cancer

Tumor progression is driven by genetic mutations, but little is known about the environmental conditions that select for these mutations. Mutations in KRAS and BRAF provide excellent examples of this central issue in cancer research. Activating KRAS and BRAF mutations are mutually exclusive during human tumorigenesis, implying their common origin and effect. Despite advances in the molecular delineation of KRAS and BRAF mutations, the specific microenvironmental pressures that drive these mutations and how these mutations alleviate these pressures are unknown. To explore this issue, we performed global gene expression analyses using paired isogenic colorectal cancer cell lines that differ only in the mutational status of their KRAS or BRAF genes, using both microarray and serial analysis of gene expression (SAGE). Surprisingly, GLUT1, encoding glucose transporter-1, was one of three genes consistently upregulated in all cells with KRAS or BRAF mutations. The mutant cells exhibited enhanced glucose uptake and lactate production and survived in low glucose conditions (0.5 mM). These phenotypes were dependent on GLUT1 expression, as targeted disruption of the GLUT1 gene abrogated those phenotypes. When cells with wild-type KRAS alleles were subjected to a low glucose environment, very few cells survived. Most surviving cells expressed high levels of GLUT1 protein and 4% of these survivors had acquired new KRAS mutations. In contrast, low oxygen condition (<0.1%) could not provide a selective growth advantage to cells with KRAS or BRAF mutations. Finally, the glycolysis inhibitor 3-bromopyruvate preferentially suppressed the growth of cells with KRAS and BRAF mutations.In conclusion, our data suggest that glucose deprivation is a major driving force underlying the acquisition of KRAS and BRAF mutations in colorectal tumors. These findings will provide profound influence on our understanding of the relationship between oncogenes and metabolic alteration in human tumors and lead to the development of new therapeutic approaches and agents for cancer treatment.