K-ras are frequently activated in human cancers. Identification of new mechanisms that regulate Ras oncogenesis is crucial to recover Ras-driven cancers. Here we show that Ras-GTP forms dimers to activate MAPK.
Firstly, we found that at endogenous expression levels KRas forms dimers, and KRas G12D, a mutant that constitutively binds GTP, activates MAPK.
Next, CCCP induced ubiquitination of mitochondria in Parkin overexpressing cells as previously reported, but not in Bcl2-L-13 overexpressing cells, excluding the involvement of ubiquitination in the regulation mechanism underlying the functions. Here, CCCP treatment increased the interaction of endogenous Bcl2-L-13 with LC3 in HEK293 cells.
Finally, we observed the same MAPK activation by artificial dimerization of monomeric KRas G12D in other cell lines. Forced dimerization of monomeric Ras-GTP caused a strong up-regulation of MAPK without having to increase the expression level of Ras-GTP. Overexpression of KRas leads to formation of higher order Ras nanoclusters.
To summary, we have shown that Ras dimer formation could be a new mechanism for regulating the biological activity of Ras, additionally to GTP-loading and membrane localization. New therapeutic agents that accomplish this might prove effective in the control of Ras-driven tumor progression and drug resistance.