Actopaxin, a new focal adhesion protein that binds paxillin LD motifs and actin and regulates cell adhesion.
Paxillin is a focal adhesion adapter protein involved in the integration of growth factor- and adhesion-mediated signal transduction pathways. Paxillin LD motifs have been demonstrated to bind to several proteins associated with remodeling of the actin cytoskeleton including the focal adhesion kinase, vinculin, and a complex of proteins comprising p95PKL, PIX, and PAK (Turner, C.E., M. C. Brown, J.A. Perrotta, M.C. Riedy, S.N. Nikolopoulos, A.R. McDonald, S. Bagrodia, S. Thomas, and P.S. Leventhal. 1999. J. Cell Biol. 145:851-863). In this study, we report the cloning and initial characterization of a new paxillin LD motif-binding protein, actopaxin. Analysis of the deduced amino acid sequence of actopaxin reveals a 42-kD protein with two calponin homology domains and a paxillin-binding subdomain (PBS). Western blotting identifies actopaxin as a widely expressed protein. Actopaxin binds directly to both F-actin and paxillin LD1 and LD4 motifs. It exhibits robust focal adhesion localization in several cultured cell types but is not found along the length of the associated actin-rich stress fibers. Similar to paxillin, it is absent from actin-rich cell-cell adherens junctions. Also, actopaxin colocalizes with paxillin to rudimentary focal complexes at the leading edge of migrating cells. An actopaxin PBS mutant incapable of binding paxillin in vitro cannot target to focal adhesions when expressed in fibroblasts. In addition, ectopic expression of the PBS mutant and/or the COOH terminus of actopaxin in HeLa cells resulted in substantial reduction in adhesion to collagen. Together, these results suggest an important role for actopaxin in integrin-dependent remodeling of the actin cytoskeleton during cell motility and cell adhesion.
Nikolopoulos
S N
SN
Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, New York 13210, USA.
Turner
C E
CE
D000185:Actinin; D000199:Actins / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002448:Cell Adhesion; D002460:Cell Line; D002465:Cell Movement; D003001:Cloning, Molecular; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D022001:Focal Adhesions / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D051419:Paxillin; D010750:Phosphoproteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D013379:Substrate Specificity; D014945:Wound Healing; D000096985:Calponins
D000185:Actinin; D000199:Actins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D008840:Microfilament Proteins; D051419:Paxillin; D010750:Phosphoproteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C486590:PARVA protein, human; D000096985:Calponins; C496061:PXN protein, human; C517887:Parva protein, rat; C496063:Pxn protein, rat; C490351:TGFB1I1 protein, human; C490352:Tgfb1i1 protein, rat