An N-terminal p120 fragment suppresses invasiveness. A , effect of p120 N-terminal fragment overexpression on RhoA and Rac1 activities. p120-depleted MDA-MB-231 cells reexpressing murine p120 isoform 1A were infected with retroviruses expressing zeocin resistance alone ( zeo ) or together with a FLAG-tagged N-terminal p120 truncation mutant containing amino acids 1-323 ( N1 ). The relative levels of active RhoA and Rac1 were determined in stable polyclonal cell lines using pull-down assays and Western blots as described earlier. Expression of N1 did not affect endogenous levels of cadherin 11 or Rac1 activation but caused a significant increase in basal RhoA activity. B , NIH3T3 fibroblasts and MDA-MB-231 cells stably expressing zeocin resistance alone or together with the N1 p120 fragment were subjected to invasion assays to determine the effect of N1 on cell invasiveness. Results are the mean ± S.E. of three independent determinations performed in duplicate. ** , p