title: A switch in RND3-RHOA signaling is critical for melanoma cell invasion following mutant-BRAF inhibition.
abstract: BACKGROUND
  The initial use of BRAF targeted therapeutics in clinical trials has demonstrated encouraging responses in melanoma patients, although a rise in drug-resistant cells capable of advancing malignant disease has been described. The current study uses BRAFV600E expressing WM793 melanoma cells to derive data aimed at investigating the molecular determinant of cell invasion following treatment with clinical BRAF inhibitors.
  
  
  RESULTS
  Small-molecule inhibitors targeting BRAF reduced MEK1/2-ERK1/2 pathway activation and cell survival; yet, viable cell subpopulations persisted. The residual cells exhibited an elongated cell shape, prominent actin stress fibers and retained the ability to invade 3-D dermal-like microenvironments. BRAF inhibitor treatments were associated with reduced expression of RND3, an antagonist of RHOA activation, and elevated RHOA-dependent signaling. Restoration of RND3 expression or RHOA knockdown attenuated the migratory ability of residual cells without affecting overall cell survival. The invasive ability of BRAF inhibitor treated cells embedded in collagen gels was diminished following RND3 re-expression or RHOA depletion. Conversely, melanoma cell movement in the absence of BRAF inhibition was unaffected by RND3 expression or RHOA depletion.
  
  
  CONCLUSIONS
  These data reveal a novel switch in the requirement for RND3 and RHOA in coordinating the movement of residual WM793 cells that are initially refractive to BRAF inhibitor therapy. These results have important clinical implications because they suggest that combining BRAF inhibitors with therapies that target the invasion of drug-resistant cells could aid in controlling disease relapse.
authors.affiliation: Center for Cell Biology and Cancer Research, MC-165, Albany Medical College, 47 New Scotland Avenue, Albany, NY 12206, USA. KleinR@mail.amc.edu
authors.forename: R Matthew
authors.initials: RM
authors.lastname: Klein
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Higgins
mesh_terms: D019943:Amino Acid Substitution; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D055785:Gene Knockdown Techniques; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D050505:Mutant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D018874:Spheroids, Cellular / Q000187:drug effects / Q000473:pathology; D013449:Sulfonamides / Q000494:pharmacology; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D007211:Indoles; D050505:Mutant Proteins; C528407:PLX 4720; D011993:Recombinant Fusion Proteins; C508204:SB-590885; D013449:Sulfonamides; C066737:RHOA protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; C508705:RND3 protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein