Beta 1 integrin-dependent and -independent polymerization of fibronectin.
The mouse cell line GD25, which lacks expression of the beta 1 family of integrin heterodimers due to disruption of the beta 1 integrin subunit gene, was used for expression of full-length cDNA coding for splice variant A of the mouse beta 1 integrin subunit. In a stably transformed clone (GD25-beta 1A), the expressed protein was found to form functional heterodimeric receptors together with the subunits alpha 3, alpha 5, and alpha 6. Both GD25 and GD25-beta 1A attached to fibronectin and formed focal contacts which contained alpha v beta 3, but no detectable alpha 5 beta 1A. The presence of GRGDS peptide allowed alpha 5 beta 1A to locate to focal contacts of GD25-beta 1A cultured on fibronectin, while the beta 1-null GD25 cells were unable to attach under these conditions. Affinity chromatography revealed that alpha 5 beta 1A and alpha v beta 3 could bind to a large cell-binding fragment of fibronectin. alpha 5 beta 1A strongly promoted polymerization of fibronectin into a fibrillar network on top of the cells. Whereas little alpha v beta 3 was colocalized with the fibronectin fibrils in GD25-beta 1A cells, this integrin was able to support fibronectin fibril polymerization in GD25 cells. However, the alpha v beta 3-induced polymerization was less efficient and occurred mainly in dense cultures of the GD25 cells. Thus, while both alpha 5 beta 1A and alpha v beta 3 are able to support adhesion to fibronectin, alpha v beta 3 dominates in the formation of focal contacts, and alpha 5 beta 1A has a prime function in fibronectin matrix assembly. This is the first report on fibronectin matrix assembly in the absence of beta 1 integrins.
Wennerberg
K
K
Department of Medical and Physiological Chemistry, Biomedical Center, Uppsala, Sweden.
Lohikangas
L
L
Gullberg
D
D
Pfaff
M
M
Johansson
S
S
Fässler
R
R
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D015152:Blotting, Northern; D002448:Cell Adhesion; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D005353:Fibronectins / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D014644:Genetic Variation; D006801:Humans; D039482:Integrin alpha5; D019012:Integrin beta1 / Q000235:genetics / Q000378:metabolism*; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D011108:Polymers; D011233:Precipitin Tests; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D013234:Stem Cells; D014162:Transfection
D015703:Antigens, CD; D018076:DNA, Complementary; D005353:Fibronectins; D039482:Integrin alpha5; D019012:Integrin beta1; D016023:Integrins; D011108:Polymers; D011994:Recombinant Proteins