The interaction between paxillin and vinculin in adhesions is spatially regulated by the activity of the RhoGTPases.

<p>(A) Western blot of vinculin-YFP and myc-tagged Rac1 and RhoA mutant expression in NIH 3T3 cells used for FRET analyses. (B) Representative donor (vinculin-YFP) and FRET efficiency images indicating that in the presence of wild type (wt) or active (V12Rac1) Rac1, paxillin and vinculin are within FRET proximity. In contrast, inhibition of Rac1 (N17Rac1) or activation of RhoA (V14RhoA) results in a loss of adhesion-localized FRET. FRET image zooms highlight representative FRET pattern of cells as indicated. (C) Quantitation of average FRET efficiency of mRFP-paxillin and vinculin-YFP in all adhesions of cells expressing activation mutants of Rac1 and RhoA. (D) Adhesion area calculations for cells expressing mRFP-paxillin and vinculin-YFP with indicated Rac1 and RhoA mutants. Expression of the active V12Rac1 mutant promotes the formation of smaller adhesions, while the dominant negative N17Rac1 or active V14RhoA constructs induce an increase in adhesion area. Error bars are standard error of the mean from cells used for FRET calculations. (E) Quantitation of average FRET efficiency of mRFP-paxillin and vinculin-YFP in all adhesions of cells in the presence of vehicle (dH₂0) or 50 μM Rac1 inhibitor (NSC23766). (F) Quantitation of average adhesion area in cells treated with vehicle or 50 μM Rac1 inhibitor. Error bars are standard error of the mean and values calculated from all adhesions from a minimum of 10 cells from 3 individual experiments. * = p<0.05, ** = p<0.005 and *** = p<0.0005. (G) Representative images of NIH 3T3 cells displaying increased vinculin-YFP cytosol/membrane localization indicating positive FRET in both adhesion contacts and areas outside integrin-mediated adhesions. Treatment with 50 μM Rac1 inhibitor decreased FRET in adhesion contacts with cytosolic/membrane FRET still observed. White lines highlight vinculin-YFP-positive adhesion areas. (H) Western blots indicating an increase in endogenous vinculin recruitment to the membrane-enriched fraction of cells treated with 50 μM Rac1 inhibitor. (I) Representative Western blots indicating no effect of the Rac1 inhibitor on the ability of endogenous paxillin and vinculin to coimmunoprecipitate, n = 3 individual experiments.