Cell motility requires extensions of the plasma membrane driven by reorganization of the actin cytoskeleton. Small GTPases, particularly the Rho family, are key regulators of this process [1-3]. A second class of GTPases, the ADP-ribosylation factors (ARFs), have also been implicated in the regulation of the actin cytoskeleton and motility . ARF6 is intimately involved in the regulation of Rac activity [5-9]; however, the mechanisms by which ARF activation leads to activation of Rac remain poorly understood. We have previously shown that expression of the ARF-GEF ARNO in MDCK cells induces robust activation of Rac, the formation of large lamellipodia, and the onset of motility . We report here that ARNO-dependent activation of Rac is mediated by a bipartite Rac GEF, the Dock180/Elmo complex. Both DOCK180 and Elmo colocalize extensively with ARNO in migrating MDCK cells. Importantly, both a catalytically inactive Dock180 mutant and an Elmo mutant that fails to couple to Dock180 block ARNO-induced Rac activation and motility. In contrast, a similar mutant of the Rac GEF β-PIX fails to inhibit ARNO-induced Rac activation or motility. Together, these data suggest that ARNO and ARF6 coordinate with the Dock180/Elmo complex to promote Rac activation at the leading edge of migrating cells.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)