GIPC1/synectin, a single PDZ domain-containing protein, binds to numerous proteins and is involved in multiple biological processes, including cell migration. We reported previously that MyoGEF, a guanine nucleotide exchange factor, plays a role in regulating breast cancer cell polarization and invasion. Here, we identify GIPC1 as an interacting partner of MyoGEF. Both in vitro and in vivo binding assays show that the GIPC1 PDZ domain binds to the PDZ-binding motif at the C terminus of MyoGEF. Immunofluorescence analysis shows that GIPC1 and MyoGEF colocalize to the cell leading edge. Depletion of GIPC1 by RNAi in MDA-MB-231 cells causes cells to shift from a polarized to a rounded morphology. Matrigel invasion assays show that RNAi-mediated depletion of GIPC1 dramatically decreases MDA-MB-231 cell invasion. Notably, an anti-MyoGEF peptide antibody, whose epitope is located at the C terminus of MyoGEF, interferes with GIPC1-MyoGEF complex formation. Treatment of MDA-MB-231 cells with the anti-MyoGEF peptide antibody disrupts cell polarization and invasion. Thus, our results suggest that GIPC1-MyoGEF complex formation plays an important role in regulating MDA-MB-231 breast cancer cell polarization and invasion.