Regulation of Rap1 activity by RapGAP1 controls cell adhesion at the front of chemotaxing cells

Spatial and temporal regulation of Rap1 is required for proper myosin assembly and cell adhesion during cell migration in Dictyostelium discoideum. Here, we identify a Rap1 guanosine triphosphatase - activating protein ( GAP; RapGAP1) that helps mediate cell adhesion by negatively regulating Rap1 at the leading edge. Defects in spatial regulation of the cell attachment at the leading edge in rapGAP1(-) ( null) cells or cells over-expressing RapGAP1 ( RapGAP1(OE)) lead to defective chemotaxis. rapGAP1- cells have extended chemoattractant-mediated Rap1 activation kinetics and decreased Myoll assembly, whereas RapGAP1OE cells show reciprocal phenotypes. We see that RapGAP1 translocates to the cell cortex in response to chemoattractant stimulation and localizes to the leading edge of chemotaxing cells via an F- actin - dependent pathway. RapGAP1 localization is negatively regulated by Ctx, an F- actin bundling protein that functions during cytokinesis. Loss of Ctx leads to constitutive and uniform RapGAP1 cortical localization. We suggest that RapGAP1 functions in the spatial and temporal regulation of attachment sites through Myoll assembly via regulation of Rap1 - guanosine triphosphate.