Once bound to activated RAC1 (RAC1:GTP) or CDC42 (CDC42:GTP), IQGAP1 binds CLIP1 (CLIP-170) via the C-terminus of IQGAP1 and the N-terminus of CLIP1. CLIP1 simultaneously interacts with IQGAP1 and the positive end of microtubules. Formation of the RAC1 or CDC42 complex with IQGAP1, CLIP1 and microtubules determines the orientation of microtubules and results in a polarized cellular morphology (Fukata et al. 2002). The RAC1:GTP:IQGAP1:CLIP1 complex is also involved in the regulation of lamellipodia formation and cell invasion in human breast cancer cells (Suzuki and Takahashi 2008).