Acetylation Negatively Regulates RAS Signaling

RAS activity is controlled via interactions with GTPase activating proteins and guanine nucleotide exchange factors (GEF) that determine its nucleotide-binding state, and mutations that disrupt this regulation are common in cancer. Posttranslational modifications of RAS, including farnesylation and ubiquitination, alter its subcellular localization and are critical for its proper function. Yang and colleagues show that RAS can also be acetylated at the conserved lysine residue K104. Acetylation of this site occurred independently of RAS nucleotide-binding state and association with the plasma membrane and did not affect the intracellular trafficking of RAS. Mutation of K104 to alanine abrogated KRAS4B acetylation but did not affect the transforming ability of an activated mutant G12V KRAS4B protein in NIH3T3 cells. In contrast, mutation of this lysine to glutamine (K104Q), which mimics constitutive acetylation, reduced the ability of G12V KRAS4B to enhance proliferation and decreased focus formation, suggesting that K104 acetylation negatively modulates RAS function. Molecular dynamics simulations predicted that K104 acetylation would disrupt the stability of the Switch II domain of RAS, which is necessary for interaction with GEF proteins that promote the switch to active RAS-GTP. In support of this hypothesis, the K104Q mutation significantly decreased GEF-mediated nucleotide exchange in vitro and reduced downstream RAS signaling. Furthermore, the K104Q substitution did not affect the transforming ability of a second activated KRAS mutant (Q61H) that functions independently of GEFs. These results support a mechanism in which K104 RAS acetylation impairs GEF activity, leading to accumulation of inactive RAS-GDP and inhibition of oncogenic transformation, and suggest that modulation of RAS acetylation may be a useful cancer therapeutic strategy.

Yang MH, Nickerson S, Kim ET, Liot C, Laurent G, Spang R, et al. Regulation of RAS oncogenicity by acetylation. Proc Natl Acad Sci U S A 2012 Jun 18 [Epub ahead of print].