title: BRAF and RAS oncogenes regulate Rho GTPase pathways to mediate migration and invasion properties in human colon cancer cells: a comparative study.
abstract: BACKGROUND
  Colorectal cancer is a common disease that involves genetic alterations, such as inactivation of tumour suppressor genes and activation of oncogenes. Among them are RAS and BRAF mutations, which rarely coexist in the same tumour. Individual members of the Rho (Ras homology) GTPases contribute with distinct roles in tumour cell morphology, invasion and metastasis. The aim of this study is to dissect cell migration and invasion pathways that are utilised by BRAFV600E as compared to KRASG12V and HRASG12V oncoproteins. In particular, the role of RhoA (Ras homolog gene family, member A), Rac1 (Ras-related C3 botulinum toxin substrate 1) and Cdc42 (cell division cycle 42) in cancer progression induced by each of the three oncogenes is described.
  
  
  METHODS
  Colon adenocarcinoma cells with endogenous as well as ectopically expressed or silenced oncogenic mutations of BRAFV600E, KRASG12V and HRASG12V were employed. Signalling pathways and Rho GTPases were inhibited with specific kinase inhibitors and siRNAs. Cell motility and invasion properties were correlated with cytoskeletal properties and Rho GTPase activities.
  
  
  RESULTS
  Evidence presented here indicate that BRAFV600E significantly induces cell migration and invasion properties in vitro in colon cancer cells, at least in part through activation of RhoA GTPase. The relationship established between BRAFV600E and RhoA activation is mediated by the MEK-ERK pathway. In parallel, KRASG12V enhances the ability of colon adenocarcinoma cells Caco-2 to migrate and invade through filopodia formation and PI3K-dependent Cdc42 activation. Ultimately increased cell migration and invasion, mediated by Rac1, along with the mesenchymal morphology obtained through the Epithelial-Mesenchymal Transition (EMT) were the main characteristics rendered by HRASG12V in Caco-2 cells. Moreover, BRAF and KRAS oncogenes are shown to cooperate with the TGFβ-1 pathway to provide cells with additional transforming properties.
  
  
  CONCLUSIONS
  This study discriminates oncogene-specific cell migration and invasion pathways mediated by Rho GTPases in colon cancer cells and reveals potential new oncogene-specific characteristics for targeted therapeutics.
authors.affiliation: Laboratory of Signal Mediated Gene Expression, Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Vas, Constantinou Ave. 48, 11635, Athens, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Makrodouli
authors.forename: Eftychia
authors.initials: E
authors.lastname: Oikonomou
authors.forename: Michal
authors.initials: M
authors.lastname: Koc
authors.forename: Ladislav
authors.initials: L
authors.lastname: Andera
authors.forename: Takehiko
authors.initials: T
authors.lastname: Sasazuki
authors.forename: Senji
authors.initials: S
authors.lastname: Shirasawa
authors.forename: Alexander
authors.initials: A
authors.lastname: Pintzas
mesh_terms: D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002465:Cell Movement; D048430:Cell Shape; D003110:Colonic Neoplasms; D015536:Down-Regulation; D004789:Enzyme Activation; D058750:Epithelial-Mesenchymal Transition; D055785:Gene Knockdown Techniques; D006801:Humans; D020125:Mutation, Missense; D009361:Neoplasm Invasiveness; D015689:Oncogene Protein p21(ras) / Q000235:genetics* / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014158:Transcription, Genetic; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
chemical_list: D015820:Cadherins; C107953:RAC1 protein, human; D053773:Transforming Growth Factor beta1; C066737:RHOA protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D054460:rho-Associated Kinases; D015689:Oncogene Protein p21(ras); D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein