Dia1 and IQGAP1 interact in cell migration and phagocytic cup formation

The Diaphanous-related formin Dial nucleates actin polymerization, thereby regulating cell shape and motility. Mechanisms that control the cellular location of Dial to spatially define actin polymerization are largely unknown. In this study, we identify the cytoskeletal scaffold protein IQGAP1 as a Dial-binding protein that is necessary for its subcellular location. IQGAP1 interacts with Dial through a region within the Diaphanous inhibitory domain after the RhoA-mediated release of Dial autoinhibition. Both proteins colocalize at the front of migrating cells but also at the actin-rich phagocytic cup in macrophages. We show that IQGAP1 interaction with Dial is required for phagocytosis and phagocytic cup formation. Thus, we identify IQGAP1 as a novel component involved in the regulation of phagocytosis by mediating the localization of the actin filament nucleator Dial.