Stimulation of beta1 integrins on fibroblasts induces PDGF independent tyrosine phosphorylation of PDGF beta-receptors.
We report that integrin-mediated signaling induces a rapid and transient tyrosine phosphorylation of platelet-derived growth factor (PDGF) beta-receptors in human diploid foreskin AG 1518 fibroblasts. A transient tyrosine phosphorylation of PDGF beta-receptors was evident one and two hours after cells had been plated on collagen type I and fibronectin, as well as on immobilized anti-integrin subunit IgG, but not on poly-L-lysine. In contrast EGF or PDGF alpha-receptors were not phosphorylated on tyrosine residues under these conditions. Tyrosine phosphorylation of PDGF beta-receptors induced by plating on collagen type I was inhibited by cytochalasin D and herbimycin A, unaffected by cycloheximide and enhanced by orthovanadate. Furthermore, a transient phosphorylation of PDGF beta-receptors occurred when AG 518 fibroblasts were cultured in three-dimensional collagen lattices or exposed to external strain exerted through centrifugation. The latter effect was evident already after two minutes. Clustering of cell surface beta1 integrins led to PDGF beta-receptor phosphorylation both in suspended and firmly attached AG 1518 fibroblasts. Plating of cells on collagen type I, fibronectin, and anti-beta1-integrin IgG resulted in the formation of PDGF beta-receptor aggregates as detected by immunofluorescence. Suramin or anti-PDGF-BB IgG had no effect on the plating-induced tyrosine phosphorylation of PDGF beta-receptors. PDGF-B chain mRNA, or protein, were not detected in AG 1518 fibroblasts. Our data suggest that a ligand-independent PDGF beta-receptor activation during cell adhesion and early phases of cell spreading is involved in integrin-mediated signaling in fibroblasts, and constitutes parts of a mechanism for cells to respond during the dynamic phases of externally applied tension as well as fibroblast-mediated tension during cell adhesion and collagen gel contraction.
Sundberg
C
C
Department of Medical and Physiological Chemistry, Biomedical Center, Uppsala, Sweden.
Rubin
K
K
D002448:Cell Adhesion; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D020797:Receptor, Platelet-Derived Growth Factor beta; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D019012:Integrin beta1; D010982:Platelet-Derived Growth Factor; D014443:Tyrosine; D020797:Receptor, Platelet-Derived Growth Factor beta; D017479:Receptors, Platelet-Derived Growth Factor