title: Rif-mDia1 interaction is involved in filopodium formation independent of Cdc42 and Rac effectors.
abstract: Filopodia are cellular protrusions important for axon guidance, embryonic development, and wound healing. The Rho GTPase Cdc42 is the best studied inducer of filopodium formation, and several of its effectors and their interacting partners have been linked to the process. These include IRSp53, N-WASP, Mena, and Eps8. The Rho GTPase, Rif, also drives filopodium formation. The signaling pathway by which Rif induces filopodia is poorly understood, with mDia2 being the only protein implicated to date. It is thus not clear how distinct the Rif-driven pathway for filopodium formation is from the one mediated by Cdc42. In this study, we characterize the dynamics of Rif-induced filopodia by time lapse imaging of live neuronal cells and show that Rif drives filopodium formation via an independent pathway that does not involve the Cdc42 effectors N-WASP and IRSp53, the IRSp53 binding partner Mena, or the Rac effectors WAVE1 and WAVE2. Rif formed filopodia in the absence of N-WASP or Mena and when IRSp53, WAVE1, or WAVE2 was knocked down by RNAi. Rif-mediated filopodial protrusion was instead reduced by silencing mDia1 expression or overexpressing a dominant negative mutant of mDia1. mDia1 on its own was able to form filopodia. Data from acceptor photobleaching FRET studies of protein-protein interaction demonstrate that Rif interacts directly with mDia1 in filopodia but not with mDia2. Taken together, these results suggest a novel pathway for filopodia formation via Rif and mDia1.
authors.affiliation: Institute of Medical Biology, 8A Biomedical Grove, Immunos, Singapore 138648.
authors.forename: Wah Ing
authors.initials: WI
authors.lastname: Goh
authors.forename: Thankiah
authors.initials: T
authors.lastname: Sudhaharan
authors.forename: Kim Buay
authors.initials: KB
authors.lastname: Lim
authors.forename: Kai Ping
authors.initials: KP
authors.lastname: Sem
authors.forename: Chew Ling
authors.initials: CL
authors.lastname: Lau
authors.forename: Sohail
authors.initials: S
authors.lastname: Ahmed
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D000080865:Formins; D055785:Gene Knockdown Techniques; D051379:Mice; D008840:Microfilament Proteins; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D011554:Pseudopodia / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051300:Wiskott-Aldrich Syndrome Protein Family / Q000235:genetics / Q000378:metabolism; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal / Q000235:genetics / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C539986:Baiap2 protein, mouse; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; C491464:Diap1 protein, mouse; C102176:Enah protein, mouse; D000080865:Formins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; C492303:Wasf2 protein, mouse; C495772:Wasl protein, mouse; D051300:Wiskott-Aldrich Syndrome Protein Family; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; D051057:Proto-Oncogene Proteins c-akt; D020764:cdc42 GTP-Binding Protein