Differences in phosphatase modulation of α4 β1 and α5 β1 integrin-mediated adhesion and migration of B16F1 cells

It is well established that a biphasic relationship exists between the adhesive strength of β1 integrins and their ability to mediate cell movement. Thus, cell movement increases progressively with adhesive strength, but beyond a certain point of optimal interaction, cell movement is reduced with further increases in adhesive function. The interplay between the various kinase and phosphatase activities provides the balance in β1 integrin-mediated cell adhesion and migration. In the present study, the significance of protein tyrosine phosphatases (PTP) and ser/thr protein phosphatases (PP) in α4β1 and α5β1 integrin-mediated mouse melanoma B16F1 cell anchorage and migration on fibronectin was characterized using phosphatase inhibitors. At low fibronectin concentration, α5β1 functioned as the predominant receptor for cell movement; a role for α4β1 in B16F1 cell migration increased progressively with fibronectin concentration. Treatment of B16F1 cells with PTP inhibitors, sodium orthovanadate (Na3VO4) and phenylarsine oxide (PAO), or PP-1/2A inhibitor, okadaic acid (OA), abolished cell movement. Inhibition of cell movement by PAO and OA was associated by a reduction in the adhesive strength of α4β1 and α5β1. In contrast, treatment of B16F1 cells with Na3VO4 resulted in selective stimulation of the adhesive function of α5β1, but not α4β1. Therefore, our results demonstrate that (i) both PTP and PP-1/2A have roles in cell movement, (ii) modulation of cell movement by PTP and PP-1/2A may involve either a stimulation or reduction of β1 integrin adhesive strength, and (iii) distinct phosphatase-mediated signaling pathways for differential regulation of the various β1 integrins exist. Key words: phosphatases, integrins, cell movement, cell adhesion.