Ras-GTP dimers activate the Mitogen-Activated Protein Kinase (MAPK) pathway.

Abstract

Rat sarcoma (Ras) GTPases regulate cell proliferation and survival through effector pathways including Raf-MAPK, and are the most frequently mutated genes in human cancer. Although it is well established that Ras activity requires binding to both GTP and the membrane, details of how Ras operates on the cell membrane to activate its effectors remain elusive. Efforts to target mutant Ras in human cancers to therapeutic benefit have also been largely unsuccessful. Here we show that Ras-GTP forms dimers to activate MAPK. We used quantitative photoactivated localization microscopy (PALM) to analyze the nanoscale spatial organization of PAmCherry1-tagged KRas 4B (hereafter referred to KRas) on the cell membrane under various signaling conditions. We found that at endogenous expression levels KRas forms dimers, and KRas(G12D), a mutant that constitutively binds GTP, activates MAPK. Overexpression of KRas leads to formation of higher order Ras nanoclusters. Conversely, at lower expression levels, KRas(G12D) is monomeric and activates MAPK only when artificially dimerized. Moreover, dimerization and signaling of KRas are both dependent on an intact CAAX (C, cysteine; A, aliphatic; X, any amino acid) motif that is also known to mediate membrane localization. These results reveal a new, dimerization-dependent signaling mechanism of Ras, and suggest Ras dimers as a potential therapeutic target in mutant Ras-driven tumors.

• Authors: Xiaolin Nan, Tanja M Tamgüney, Eric A Collisson, Li-Jung Lin, Cameron Pitt, Jacqueline Galeas, Sophia Lewis, Joe W Gray, Frank McCormick, Steven Chu
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 112 Issue 26 Pg. 7996-8001 (Jun 30 2015) ISSN: 1091-6490 [Electronic] United States
• PMID: 26080442 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Guanosine Triphosphate
• Mitogen-Activated Protein Kinases
• ras Proteins

Topics

• Animals
• Cell Line
• Cricetinae
• Dimerization
• Enzyme Activation
• Guanosine Triphosphate (metabolism)
• MAP Kinase Signaling System
• Mitogen-Activated Protein Kinases (metabolism)
• ras Proteins (metabolism)