Rac1 is important for dissociation of cells during scattering, but whether its activation alone is sufficient to induce complete scattering is not known. To test this, we created an inducible MCF7 cell line that expresses dominant active Rac1. Although induction of dominant active Rac1 resulted in dissociation of cells, their scattering was incomplete. We co-expressed dominant active MKK1a, an activator of ERK, and dominant active Rac1. In this case, cells completely scattered. These results suggest that not only Rac1 but also the MEK1 pathway is required for dissociation and complete scattering of MCF7 cells treated with HRG-beta 1. (C) 2013 Elsevier Inc. All rights reserved.