Identification of CD9 extracellular domains important in regulation of CHO cell adhesion to fibronectin and fibronectin pericellular matrix assembly.
CD9, a 24-kDa member of the tetraspanin family, influences cellular growth and development, activation, adhesion, and motility. Our investigation focuses on the hypothesis that the CD9 second extracellular loop (EC2) is important in modulating cell adhesive events. Using a Chinese hamster ovary (CHO) cell expression system, we previously reported that CD9 expression inhibited cell adhesion to fibronectin and fibronectin matrix assembly. For the first time, a functional epitope on CD9 EC2 that regulates these processes is described. Binding of mAb7, an EC2-specific anti-CD9 monoclonal antibody, reversed the CD9 inhibitory activity on CHO cell adhesion and fibronectin matrix assembly. This reversal of cell phenotype also was observed in CHO cells expressing CD9 EC2 truncations. Furthermore, our data showed that the EC2 sequence (173)LETFTVKSCPDAIKEVFDNK(192) was largely responsible for the CD9-mediated CHO cell phenotype. Two peptides, (135)K-V(172) (peptide 5b) and (168)P-I(185) (peptide 6a), selectively blocked mAb7 binding to soluble CD9 and to CD9 on intact cells. These active peptides reversed the influence of CD9 expression on CHO cell adhesion to fibronectin. In addition, confocal microscopy revealed that CD9 colocalized with the integrin alpha(5)beta(1) and cytoskeletal F-actin in punctate clusters on the cell surface, particularly at the cell margins. Immunoprecipitation studies confirmed CD9 association with beta(1) integrin. The cellular distribution and colocalization of focal adhesion kinase and alpha-actinin with cytoskeletal actin was also influenced by CD9 expression. Thus, CD9 may exhibit its effect by modulating the composition of adhesive complexes important in facilitating cell adhesion and matrix assembly.
Cook
George A
GA
Vascular Biology Center of Excellence, Department of Medicine, The University of Tennessee Health Science Center, Memphis, TN 38163, USA.
Longhurst
Celia M
CM
Grgurevich
Svetozar
S
Cholera
Shila
S
Crossno
Joseph T
JT
Jennings
Lisa K
LK
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D016466:CHO Cells / Q000166:cytology*; D002448:Cell Adhesion / Q000502:physiology; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism; D000939:Epitopes / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D039081:Integrin alpha5beta1 / Q000378:metabolism; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D017384:Sequence Deletion; D060245:Tetraspanin 29; D014162:Transfection
D000199:Actins; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C554869:CD9 protein, human; D000939:Epitopes; D005353:Fibronectins; D039081:Integrin alpha5beta1; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D060245:Tetraspanin 29; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human