Rac Activation and Inactivation Control Plasticity of Tumor Cell Movement

Abstract

Tumor cells exhibit two different modes of individual cell movement. Mesenchymal-type movement is characterized by an elongated cellular morphology and requires extracellular proteolysis. In amoeboid movement, cells have a rounded morphology, are less dependent on proteases, and require high Rho-kinase signaling to drive elevated levels of actomyosin contractility. These two modes of cell movement are interconvertible. We show that mesenchymal-type movement in melanoma cells is driven by activation of the GTPase Rac through a complex containing NEDD9, a recently identified melanoma metastasis gene, and DOCK3, a Rac guanine nucleotide exchange factor. Rac signals through WAVE2 to direct mesenchymal movement and suppress amoeboid movement through decreasing actomyosin contractility. Conversely, in amoeboid movement, Rho-kinase signaling activates a Rac GAP, ARHGAP22, that suppresses mesenchymal movement by inactivating Rac. We demonstrate tight interplay between Rho and Rac in determining different modes of tumor cell movement, revealing how tumor cells switch between different modes of movement.

The actin-associating protein Tm5NM1 blocks mesenchymal motility without transition to amoeboid motility

“…Rac GTPase activity critically regulates pseudopodial protrusions and mesenchymal cell migration in 3D gels (Sanz-Moreno et al, 2008;Friedl and Wolf, 2010), separately confirmed in the cell lines used in the present study by the use of dominant-negative Rac. Downstream from Rac, Arp2/3 initiates short-branched actin filaments that push against the cell membrane, leading to membrane protrusion.…”

“…Videos were then converted to MPEG-4 files using Total video converter (OJOsoft, www.ojosoft.com). Cell invasion assays were adapted from a previously described method (Sanz-Moreno et al, 2008). Approximately 2.5 Â 10 4 cells were seeded within 1.7 mg/ml collagen gel containing o1% serum in 96-well flat bottom plates (100 ml of gel per well).…”

“…Mesenchymal migration is characterized by cell elongation and branching polarized protrusions in the direction of migration. The chief properties that define mesenchymal migration include activation of the small GTPase Rac (Sanz-Moreno et al, 2008;Yamazaki et al, 2009), targeted expression of matrix metalloproteases (Sahai and Marshall, 2003;Wolf et al, 2003) and the regulated formation and disassembly of integrin receptor-mediated extracellular matrix adhesions mediated by the activity of Src kinase Carragher et al, 2006). In contrast, amoeboid migration is characterized by rounded cell morphology and is associated with non-apoptotic plasma membrane blebbing (Sahai and Marshall, 2003).…”

“…In contrast, amoeboid migration is characterized by rounded cell morphology and is associated with non-apoptotic plasma membrane blebbing (Sahai and Marshall, 2003). Rapid expansion and contraction allow amoeboid cells to squeeze through obstructing matrix, and this is highly dependant on actomyosin contractility (Sahai and Marshall, 2003;Sanz-Moreno et al, 2008;Friedl and Wolf, 2010). The migration of amoeboid cells is facilitated by the RhoA GTPase effector molecule Rho-associated kinase (ROCK), independent of matrix metalloprotease activity and less dependant on integrin receptor adhesion to the extracellular matrix (Friedl andWolf, 2003, 2010;Carragher et al, 2006).…”

“…Many cells are competent to undergo transition between mesenchymal and amoeboid migration modes (Carragher et al, 2006;Yamazaki et al, 2009), and manipulating the principle molecular regulators can induce cells to switch between these modes. Thus, blocking mesenchymal migration by treatment with protease inhibitors (PIs) or blocking Rac activity (Sanz-Moreno et al, 2008) causes cells to switch to an amoeboid motility mode. Notably, cell migration speeds are unaffected following mesenchymal to amoeboid transition .…”