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Title: Ras-GTP dimers activate the mitogen-activated protein kinase (MAPK) pathway

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 KRasG12D, a mutant that constitutively binds GTP, activates MAPK. Overexpression of KRas leads to formation of higher order Ras nanoclusters. Conversely, at lower expression levels, KRasG12D 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 dimersmore » as a potential therapeutic target in mutant Ras-driven tumors.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [2] ;  [5] ;  [6] ;  [2] ;  [7]
  1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Oregon Health and Science Univ., Portland, OR (United States)
  2. Univ. of California, San Francisco, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, San Francisco, CA (United States)
  4. Oregon Health and Science Univ., Portland, OR (United States)
  5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Oregon Health and Science Univ., Portland, OR (United States); Univ. of California, San Francisco, CA (United States)
  7. Stanford Univ., Stanford, CA (United States)
Publication Date:
OSTI Identifier:
1221216
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 112; Journal Issue: 26; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES Ras dimer; MAPK signaling; cancer; single molecule imaging; superresolution microscopy