The association between R-Ras and FLNa enhances integrin activation.

<p><b>A</b>) M2 cells express a subset of integrins on their surface. FACS analysis of a subset of integrins expressed on the surface of M2 cells. M2 cells express α5 and β1 subunits on their surface but not αvβ3. <b>B</b>) Forced expression of activated R-Ras promotes integrin activation in M2 cells as determined by the 3Fn-(9–11) activation assay. M2 (FLNa-) cells were transiently transfected with expression vectors encoding GFP as transfection reporter and FLNa, constitutively active R-Ras G38V alone or ±FLNa or FLNaΔ3. Cells were harvested and analyzed by two-color FACS for transfected cells and 3FN-(9–11) binding. Shown on the <i>Y-Axis</i> is mean activation index ±S.E. of three independent experiments. Constitutively expressed active R-Ras G38V and FLNa increased the activation index more than R-Ras alone. FLNaΔ3 did not block R-Ras-mediated activation compared with controls. Statistically significant differences are reported in the graph as <i>P</i> values (Student's <i>t</i>-test), *, <i>P</i><0.05 **, <i>P</i><0.04 <b>C</b>) Western blot of R-Ras levels when transiently transfected with R-Ras G38V. Tubulin was used as a loading control. Data represent at least 3 independent experiments.