Rap1 controls cell adhesion and cell motility through the regulation of myosin II

Abstract

We have investigated the role of Rap1 in controlling chemotaxis and cell adhesion in Dictyostelium discoideum. Rap1 is activated rapidly in response to chemoattractant stimulation, and activated Rap1 is preferentially found at the leading edge of chemotaxing cells. Cells expressing constitutively active Rap1 are highly adhesive and exhibit strong chemotaxis defects, which are partially caused by an inability to spatially and temporally regulate myosin assembly and disassembly. We demonstrate that the kinase Phg2, a putative Rap1 effector, colocalizes with Rap1–guanosine triphosphate at the leading edge and is required in an in vitro assay for myosin II phosphorylation, which disassembles myosin II and facilitates filamentous actin–mediated leading edge protrusion. We suggest that Rap1/Phg2 plays a role in controlling leading edge myosin II disassembly while passively allowing myosin II assembly along the lateral sides and posterior of the cell.

Dynamic Localization of the Actin-Bundling Protein Cortexillin I during Cell Migration

“…In agreement with our view, recent studies have proposed that myosin II and IQGAP/cortexillin are important negative regulators of leading-edge function and restrict the site of pseudopod formation to the leading edge of moving cells (Jeon et al, 2007b;Ren et al, 2009). In response to chemoattractant stimulation, cells rapidly activate a series of signal- ing pathways including Ras/Rap1 proteins, PI3K and TORC2, and their effectors Akt/PKB and PKBR1 at the leading edge of the cell, leading to F-actin polymerization, pseudopod formation, and directional movement up the gradient (Charest et al, 2010;Kolsch et al, 2008;Kortholt and van Haastert, 2008).…”

“…Upon chemoattractant stimulation, there is a rapid release of cortexillin I from the cortex followed by a transient translocation to the cell cortex with a peak at ~5 s and a subsequent decrease to the basal level. An initial delocalization from the cell cortex upon stimulation is also found in the translocation kinetics of several proteins including myosin II, PTEN, and PakA (Chung and Firtel, 1999;Funamoto et al, 2002;Jeon et al, 2007b), but the subsequent transient translocation of cortexillin I to the cortex within 10 s is not observed with other proteins. The transient translocation kinetics of cortexillin I, except the initial delocalization of the proteins, is similar to that of the Arp2/3 complex, a nucleator of F-actin assembly.…”

“…The IQGAP/cortexillin complexes are involved in regulating cortical mechanics. It has been recently suggested that myosin II and IQGAP/cortexillin play important roles in regulating the ability of cells to restrict the F-actin assembly site and pseudopod formation at the leading edge of moving cells (Jeon et al, 2007b;.…”

Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity

“…In wild-type cells, Rap1S17N has been shown to increase myosin IIB at the cell cortex which leads to cell retraction and decreased adhesion (44). As shown in Fig.…”

“…Because the small G protein Rap1 has been demonstrated to provide a supportive role in Dictyostelium protrusion generation and substrate adhesion, we examined how the expression of the dominant negative Rap1S17N-myc would affect adhesion in the confirmed RAM strains (41)(42)(43)(44)(45). In wild-type cells, Rap1S17N has been shown to increase myosin IIB at the cell cortex which leads to cell retraction and decreased adhesion (44).…”