Integrin alpha 2 cytoplasmic domain deletion effects: loss of adhesive activity parallels ligand-independent recruitment into focal adhesions.
Chinese hamster ovary (CHO) cells transfected with the integrin alpha 2 subunit formed a stable VLA-2 heterodimer that mediated cell adhesion to collagen. Within CHO cells spread on collagen, but not fibronectin, wild-type alpha 2 subunit localized into focal adhesion complexes (FACs). In contrast, alpha 2 with a deleted cytoplasmic domain was recruited into FACs whether CHO cells were spread on collagen or fibronectin. Thus, as previously seen for other integrins, the alpha 2 cytoplasmic domain acts as a negative regulator, preventing indiscriminate integrin recruitment into FACs. Notably, ligand-independent localization of the VLA-2 alpha 2 subunit into FACs was partially prevented if only one or two amino acids were present in the alpha 2 cytoplasmic domain (beyond the conserved GFFKR motif) and was completely prevented by four to seven amino acids. The addition of two alanine residues (added to GFFKR) also partially prevented ligand-independent localization. In a striking inverse correlation, the same mutants showing increased ligand-independent recruitment into FACs exhibited diminished alpha 2-dependent adhesion to collagen. Thus, control of VLA-2 localization may be closely related to the suppression of cell adhesion to collagen. In contrast to FAC localization and collagen adhesion results, VLA-2-dependent binding and infection by echovirus were unaffected by either alpha 2 cytoplasmic domain deletion or exchange with other cytoplasmic domains.
Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
S
S
Kawaguchi
J M
JM
Bergelson
R W
RW
Finberg
M E
ME
Hemler
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002448:Cell Adhesion; D003094:Collagen; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D029822:Enterovirus B, Human / Q000378:metabolism; D005353:Fibronectins; D016023:Integrins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D008024:Ligands; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016029:Receptors, Very Late Antigen / Q000378:metabolism*; D011991:Receptors, Virus / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D005353:Fibronectins; D016023:Integrins; D008024:Ligands; D016029:Receptors, Very Late Antigen; D011991:Receptors, Virus; D011993:Recombinant Fusion Proteins; D003094:Collagen