Rac function is critical for cell migration but not required for spreading and focal adhesion formation

Abstract

SummaryCell migration is commonly accompanied by protrusion of membrane ruffles and lamellipodia. In two-dimensional migration, protrusion of these thin sheets of cytoplasm is considered relevant to both exploration of new space and initiation of nascent adhesion to the substratum. Lamellipodium formation can be potently stimulated by Rho GTPases of the Rac subfamily, but also by RhoG or Cdc42. Here we describe viable fibroblast cell lines genetically deficient for Rac1 that lack detectable levels of Rac2 and Rac3. Rac-deficient cells were devoid of apparent lamellipodia, but these structures were restored by expression of either Rac subfamily member, but not by Cdc42 or RhoG. Cells deficient in Rac showed strong reduction in wound closure and random cell migration and a notable loss of sensitivity to a chemotactic gradient. Despite these defects, Rac-deficient cells were able to spread, formed filopodia and established focal adhesions. Spreading in these cells was achieved by the extension of filopodia followed by the advancement of cytoplasmic veils between them. The number and size of focal adhesions as well as their intensity were largely unaffected by genetic removal of Rac1. However, Rac deficiency increased the mobility of different components in focal adhesions, potentially explaining how Rac – although not essential – can contribute to focal adhesion assembly. Together, our data demonstrate that Rac signaling is essential for lamellipodium protrusion and for efficient cell migration, but not for spreading or filopodium formation. Our findings also suggest that Rac GTPases are crucial to the establishment or maintenance of polarity in chemotactic migration.

Rac1-dependent recruitment of PAK2 to G2phase centrosomes and their roles in the regulation of mitotic entry

“…As opposed to the parental control clone (Rac1 fl/fl ) and shown previously, 19 Rac1 −/− MEFs clone 3 did not express Rac1 (Fig. 4E).…”

Doxorubicin Induces Lamellipodia Formation and Cell Migration

“…Nevertheless, Rac1 is not the only protein that regulate actin structures, RhoG or Cdc42 also play role in these structure (Steffen, et al, 2013). In this study, doxorubicin reduce Rac1 expression of 4T1 and MCF-7/HER2 cells.…”

Reggie-1/Flotillin-2 regulates integrin trafficking and focal adhesion turnover via Rab11a

“…These reports together with our data indicate that reggie and Rab11 might regulate Rac1 recruitment and its spatially confined activation. A role of Rac in paxillin turnover in FAs in mouse embryonic fibroblasts has also been suggested (Steffen et al, 2013). Moreover, RCP/Rab11-driven recycling of ␣5␤1-integrin controls the activation of Rac and RhoA in different cell lines (A2780, MDA-MB-231 and HT1080 cells) (Jacquemet et al, 2013).…”

“…Cell movement and spreading are influenced by Rac activity (Nobes and Hall, 1999) and Rac was suggested to contribute to FA regulation through adhesion component stabilization (Steffen et al, 2013). To analyze whether the activation of Rac1 was affected in shR1 cells, we determined the amount of GTP-bound Rac1 by affinity-purification with the Rac1-binding protein Pak1-PBD, bound to agarose.…”