Differential Role of Protein Tyrosine Phosphorylation/dephosphorylation in Affinity Regulation of β1 and β3 Integrin in Human Fibroblasts

Abstract

We investigated the effects of protein tyrosine phosphatase inhibitors, pervanadate and phenyl-arsine oxide (PAO), on the β1 and β3 integrin-mediated cell-substrate interaction using normal diploid human fibroblast. Pervanadate treatment of the cells in suspension state resulted in highly elevated levels of cellular protein tyrosine phosphorylation accompanied by loss of β1 integrin-mediated adhesion to substrata (i.e., collagen and laminin). In contrast, β3 integrin-mediated adhesion to substrata (i.e., fibronectin and vitronectin) of these cells was less affected. Moreover, pervanadate could reverseβ1 integrin-dependent adhesion, and cells already adhered on collagen or laminin, but not on fibronectin or vitronectin, came off within 30 min upon pervanadate treatment. These effects are likely to be directly mediated by increased cellular protein tyrosine phosphorylation, because another chemical compound, PAO, which also inhibits protein tyrosine phosphatase through a quite different mechanism, also exhibited the specific deterioration ofβ1 integrin-mediated cell-substrate interaction. Upon treatment with these protein tyrosine phosphatase inhibitors, the well developed actin stress fibers were disrupted resulting in the rounding up of cells on fibronectin and vitronectin substrate though they were still attached to theβ3 integrin-dependent substrates. Using immunoprecipitation and anti-phosphotyrosine immunoblotting, β1 integrin itself was shown not to be tyrosine phosphorylated. These results indicate that affinity regulation ofβ1 and β3 integrin is differentially controlled and that the specific regulation ofβ1 integrin is due to certain cellular component(s) whose activity is modulated by tyrosine phosphorylation/dephosphorylation.