title: A novel actin bundling/filopodium-forming domain conserved in insulin receptor tyrosine kinase substrate p53 and missing in metastasis protein.
abstract: Insulin receptor tyrosine kinase substrate p53 (IRSp53) has been identified as an SH3 domain-containing adaptor that links Rac1 with a Wiskott-Aldrich syndrome family verprolin-homologous protein 2 (WAVE2) to induce lamellipodia or Cdc42 with Mena to induce filopodia. The recruitment of these SH3-binding partners by IRSp53 is thought to be crucial for F-actin rearrangements. Here, we show that the N-terminal predicted helical stretch of 250 amino acids of IRSp53 is an evolutionarily conserved F-actin bundling domain involved in filopodium formation. Five proteins including IRSp53 and missing in metastasis (MIM) protein share this unique domain and are highly conserved in vertebrates. We named the conserved domain IRSp53/MIM homology domain (IMD). The IMD has domain relatives in invertebrates but does not show obvious homology to any known actin interacting proteins. The IMD alone, derived from either IRSp53 or MIM, induced filopodia in HeLa cells and the formation of tightly packed parallel F-actin bundles in vitro. These results suggest that IRSp53 and MIM belong to a novel actin bundling protein family. Furthermore, we found that filopodium-inducing IMD activity in the full-length IRSp53 was regulated by active Cdc42 and Rac1. The SH3 domain was not necessary for IMD-induced filopodium formation. Our results indicate that IRSp53, when activated by small GTPases, participates in F-actin reorganization not only in an SH3-dependent manner but also in a manner dependent on the activity of the IMD.
authors.affiliation: Department of Structural Analysis, National Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Yamagishi
authors.forename: Michitaka
authors.initials: M
authors.lastname: Masuda
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohki
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Onishi
authors.forename: Naoki
authors.initials: N
authors.lastname: Mochizuki
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D002460:Cell Line; D019992:Databases as Topic; D004305:Dose-Response Relationship, Drug; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011554:Pseudopodia / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D051300:Wiskott-Aldrich Syndrome Protein Family; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D018909:src Homology Domains
chemical_list: D000199:Actins; C119539:BAIAP2 protein, human; D008164:Luminescent Proteins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; C120152:WASF2 protein, human; D051300:Wiskott-Aldrich Syndrome Protein Family; D049452:Green Fluorescent Proteins; D005982:Glutathione Transferase; D020558:GTP Phosphohydrolases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein