The alpha 5 beta 1 integrin fibronectin receptor, but not the alpha 5 cytoplasmic domain, functions in an early and essential step in fibronectin matrix assembly.
The alpha 5 beta 1 integrin mediates cell adhesion and migration on fibronectin, a glycoprotein critical for normal vertebrate embryonic development. Indirect evidence reported to date suggests that this receptor also functions in the deposition of fibronectin matrices. We used a molecular genetic approach to critically evaluate this role of alpha 5 beta 1 integrins. Mutant Chinese hamster ovary (CHO) cells deficient in alpha 5 integrin expression could not assemble a fibronectin matrix. Reconstituting alpha 5 beta 1 integrin expression by transfecting them with a full-length cDNA encoding the human alpha 5 chain completely restored fibronectin matrix assembly. CHO cells expressing an alpha 5 chain lacking the cytoplasmic domain also assembled a fibronectin matrix. Removing the cytoplasmic domain of alpha 5 appears to increase its activity in fibronectin matrix assembly. In addition to alpha 5 beta 1 integrin binding to fibronectin's RGD-containing domain, cells must bind with high affinity to fibronectin's amino-terminal 29-kDa matrix assembly domain to form a fibronectin matrix. Studies with the alpha 5-deficient CHO cells show that the expression of alpha 5 beta 1 integrin is also necessary for cells to bind fragments containing this distinct site in fibronectin and that a fibronectin matrix increases binding of the 29-kDa fragment. Thus, alpha 5 beta 1 integrins not only mediate cell adhesion to fibronectin, but also play an essential role in the assembly of a fibronectin matrix. This role includes direct binding to fibronectin and modulating a distinct binding event involving the interaction of fibronectin's amino-terminal matrix assembly domain with the cell surface.
Wu
C
C
Samuel C. Johnson Medical Research Center, Mayo Clinic Scottsdale, Arizona 85259.
Bauer
J S
JS
Juliano
R L
RL
McDonald
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism; D017469:Receptors, Fibronectin / Q000378:metabolism*
D018076:DNA, Complementary; D005353:Fibronectins; D016023:Integrins; D009842:Oligopeptides; D017469:Receptors, Fibronectin; C047981:arginyl-glycyl-aspartic acid