Oncogenic KRAS mutations modulate BAX-mediated cell death

Kirsten rat sarcoma viral oncogene homolog (KRAS) belongs to the GTPase RAS superfamily, which regulates several cell-signaling pathways involved in the control of important cellular functions, including apoptosis. Oncogenic mutations in KRAS are considered the most common gain-of-function mutations, affecting 30–50 % of colorectal cancer (CRC) patients. While RAS proteins usually play an anti-apoptotic role, little is known about the involvement of KRAS mutations in apoptosis regulation. Here, we aimed to elucidate the role of mutated human KRAS in the regulation of BAX, a key pro-apoptotic member of the Bcl-2 family. For this purpose, we took advantage of the simpler yeast model Saccharomyces cerevisiae, using cells deficient in the main yeast RAS isoform (ras2Δ) co-expressing wild-type KRAS (KRAS^WT) or the most frequent KRAS mutations found in CRC - KRAS^G12D, KRAS^G12V or KRAS^G13D, along with human BAX. We show that, in comparison with KRAS^WT, KRAS mutants confer resistance to BAX-induced death and cytochrome c (cyt c) release. The modulation of BAX by KRAS isoforms seems to result from a direct interaction between these proteins, as they co-localize at the mitochondria and there is evidence they may physically interact. We further show that acetic acid significantly increased cell death in cells expressing BAX and co-expressing oncogenic KRAS mutants, but not KRAS^WT. This suggests a potential mechanism explaining the increased sensitivity of CRC cells harboring a KRAS-activated pathway to acetate. These findings contribute to a clearer understanding of how KRAS regulate BAX function, a relevant aspect in tumor progression.