The small GTPase Rac3 interacts with the integrin-binding protein CIB and promotes integrin alpha(IIb)beta(3)-mediated adhesion and spreading.
There are only three human isoforms of the small GTPase Rac, which together regulate a variety of cellular processes, including those related to actin cytoskeletal reorganization. A role for Rac3 in integrin-mediated adhesion and spreading has not been defined. We here report that CIB, a protein that binds to the alpha(IIb)beta(3) fibrinogen receptor, interacts exclusively with activated (V12) Rac3 but not Rac1 or Rac2. Binding of V12Rac3 to CIB was mediated by the C-terminal end of Rac3 and by Rac3 membrane localization. Adhesion of cells on fibrinogen was accompanied by a specific increase in the levels of Rac3 but not Rac1 or Rac2 in the Triton-insoluble fraction of the cell. Also, CIB co-localized with active Rac3 to the periphery of cells adhering to fibrinogen. Expression of V12Rac3 and CIB stimulated alpha(IIb)beta(3)-mediated adhesion and spreading on fibrinogen. Moreover, adhesion through alpha(IIb)beta(3) caused a marked increase in the levels of endogenous GTP-bound Rac3 but not Rac1. These combined results strongly implicate Rac3 and CIB in integrin-associated cytoskeletal reorganization during alpha(IIb)beta(3)-mediated adhesion.
Haataja
Leena
L
Division of Hematology/Oncology, Section of Molecular Carcinogenesis, Childrens Hospital Los Angeles Research Institute and the Keck School of Medicine of the University of Southern California, Los Angeles, California 90027, USA.
Kaartinen
Vesa
V
Groffen
John
J
Heisterkamp
Nora
N
D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002448:Cell Adhesion; D006224:Cricetinae; D003599:Cytoskeleton / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D005340:Fibrinogen / Q000737:chemistry* / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D007150:Immunohistochemistry; D008856:Microscopy, Fluorescence; D056921:Nuclear Receptor Coactivator 3; D017830:Octoxynol / Q000494:pharmacology; D010957:Plasmids / Q000378:metabolism; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014162:Transfection; D020798:Two-Hybrid System Techniques; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D000097766:RAC2 GTP-Binding Protein
D002352:Carrier Proteins; D003902:Detergents; D005340:Fibrinogen; D005982:Glutathione Transferase; D056921:Nuclear Receptor Coactivator 3; D017830:Octoxynol; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014157:Transcription Factors; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein; D000097766:RAC2 GTP-Binding Protein