title: Raf inhibitors target ras spatiotemporal dynamics.
abstract: BACKGROUND
  The lateral segregation of Ras proteins into transient plasma membrane nanoclusters is essential for high-fidelity signal transmission by the Ras mitogen-activated protein kinase (MAPK) cascade. In this spatially constrained signaling system, the dynamics of Ras nanocluster assembly and disassembly control MAPK signal output.
  
  
  RESULTS
  We show here that BRaf inhibitors paradoxically activate CRaf and MAPK signaling in Ras transformed cells by profoundly dysregulating Ras nanocluster dynamics. Specifically, BRaf inhibitors selectively enhance the plasma membrane nanoclustering of oncogenic K-Ras and N-Ras but have no effect on H-Ras nanoclustering. Raf inhibitors are known to drive the formation of stable BRaf-CRaf and CRaf-CRaf dimers. Our results demonstrate that the presence of two Ras-binding domains in a single Raf dimer is sufficient and required to increase Ras nanoclustering, indicating that Raf dimers promote K- and N-Ras nanocluster formation by crosslinking constituent Ras proteins. Ras crosslinking increases the fraction of K-Ras and N-Ras in their cognate nanoclusters, leading to an increase in MAPK output from the plasma membrane. Intriguingly, increased MAPK signaling in BRaf inhibited cells is accompanied by significantly decreased Akt activation. We show that this signal pathway crosstalk results from a novel mechanism of competition between stabilized Raf dimers and p110α for recruitment to Ras nanoclusters.
  
  
  CONCLUSIONS
  Our findings reveal that BRaf inhibitors disrupt Ras nanocluster dynamics with significant, yet divergent, consequences for MAPK and PI3K signaling.
authors.affiliation: Department of Integrative Biology and Pharmacology, The University of Texas Medical School-Houston, 6431 Fannin Street, Houston, TX 77030, USA.
authors.forename: Kwang-jin
authors.initials: KJ
authors.lastname: Cho
authors.forename: Rinshi S
authors.initials: RS
authors.lastname: Kasai
authors.forename: Jin-Hee
authors.initials: JH
authors.lastname: Park
authors.forename: Sravanthi
authors.initials: S
authors.lastname: Chigurupati
authors.forename: Sonja J
authors.initials: SJ
authors.lastname: Heidorn
authors.forename: Dharini
authors.initials: D
authors.lastname: van der Hoeven
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Plowman
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kusumi
authors.forename: Richard
authors.initials: R
authors.lastname: Marais
authors.forename: John F
authors.initials: JF
authors.lastname: Hancock
mesh_terms: D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D019281:Dimerization; D006801:Humans; D020935:MAP Kinase Signaling System; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D019869:Phosphatidylinositol 3-Kinases; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins