FIGURE 3.

Arg phosphorylates Tyr-783 on integrin β1 in cells. A, Arg phosphorylates endogenous integrin β1 at site Tyr-783 in cells. Control or Arg-YFP-expressing Phoenix cells were pretreated overnight with STI-571 (10 μm) or DPH (30 μm) before performing Mn²⁺-mediated integrin activation assays where some conditions were treated with 2 mm Mn²⁺ to activate integrins. STI-571 suppresses and DPH enhances Mn²⁺-activated integrin Tyr-783 phosphorylation in Arg-YFP-expressing Phoenix cells. Error bars represent S.E. from n = 3. **, p < 0.01; ****, p < 0.0001; ns, not significant relative to the integrin-activated Arg-YFP condition (lane 6). B, Arg-YFP or kinase inactive Arg-K317M-YFP were expressed in Phoenix cells, and Mn²⁺-stimulated integrin activation assays were performed as above before blotting Tyr(P)-783. An Arg kinase inactive mutant (K317M) cannot promote Tyr-783 phosphorylation in cells. IB, immunoblot.