title: Focal adhesion disassembly is regulated by a RIAM to MEK-1 pathway.
abstract: Cell migration and invasion require regulated turnover of integrin-dependent adhesion complexes. Rap1-GTP-interacting adaptor molecule (RIAM) is an adaptor protein that mediates talin recruitment to the cell membrane, and whose depletion leads to defective melanoma cell migration and invasion. In this study, we investigated the potential involvement of RIAM in focal adhesion (FA) dynamics. RIAM-depleted melanoma and breast carcinoma cells displayed an increased number, size and stability of FAs, which accumulated centrally at the ventral cell surface, a phenotype caused by defective FA disassembly. Impairment in FA disassembly resulting from RIAM knockdown correlated with deficient integrin-dependent mitogen-activated protein kinase kinase (MEK)-Erk1/2 activation and, importantly, overexpression of constitutively active MEK resulted in rescue of FA disassembly and recovery of cell invasion. Furthermore, RIAM-promoted Ras homologue gene family, member A (RhoA) activation following integrin engagement was needed for subsequent Erk1/2 activation. In addition, RhoA overexpression partially rescued the FA phenotype in RIAM-depleted cells, also suggesting a functional role for RhoA downstream of RIAM, but upstream of Erk1/2. RIAM knockdown also led to enhanced phosphorylation of paxillin Tyr118 and Tyr31. However, expression of phosphomimetic and nonphosphorylatable mutants at these paxillin residues indicated that paxillin hyperphosphorylation is a subsequent consequence of the blockade of FA disassembly, but does not cause the FA phenotype. RIAM depletion also weakened the association between FA proteins, suggesting that it has important adaptor roles in the correct assembly of adhesion complexes. Our data suggest that integrin-triggered, RIAM-dependent MEK activation represents a key feedback event required for efficient FA disassembly, which could help explain the role of RIAM in cell migration and invasion.
authors.affiliation: Department of Cellular and Molecular Medicine, Centro de Investigaciones Biológicas (CSIC), 28040 Madrid,  Spain.
authors.forename: Georgina P
authors.initials: GP
authors.lastname: Coló
authors.forename: Pablo
authors.initials: P
authors.lastname: Hernández-Varas
authors.forename: John
authors.initials: J
authors.lastname: Lock
authors.forename: Rubén A
authors.initials: RA
authors.lastname: Bartolomé
authors.forename: Nohemí
authors.initials: N
authors.lastname: Arellano-Sánchez
authors.forename: Staffan
authors.initials: S
authors.lastname: Strömblad
authors.forename: Joaquin
authors.initials: J
authors.lastname: Teixidó
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008545:Melanoma / Q000201:enzymology / Q000473:pathology; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D051419:Paxillin / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12 / Q000378:metabolism; D015854:Up-Regulation; D020742:rhoA GTP-Binding Protein / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: C493340:APBB1IP protein, human; D048868:Adaptor Proteins, Signal Transducing; D008565:Membrane Proteins; D051419:Paxillin; D019000:Phosphotyrosine; D051416:Focal Adhesion Protein-Tyrosine Kinases; D019061:src-Family Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; D054594:Protein Tyrosine Phosphatase, Non-Receptor Type 12; D020742:rhoA GTP-Binding Protein