Interplay between Rac and Rho in the control of substrate contact dynamics.
BACKGROUND
Substrate anchorage and cell locomotion entail the initiation and development of different classes of contact sites, which are associated with the different compartments of the actin cytoskeleton. The Rho-family GTPases are implicated in the signalling pathways that dictate contact initiation, maturation and turnover, but their individual roles in these processes remain to be defined.


RESULTS
We monitored the dynamics of peripheral, Rac-induced focal complexes in living cells in response to perturbations of Rac and Rho activity and myosin contractility. We show that focal complexes formed in response to Rac differentiated into focal contacts upon upregulation of Rho. Focal complexes were dissociated by inhibitors of myosin-II-dependent contractility but not by an inhibitor of Rho-kinase. The downregulation of Rac promoted the enlargement of focal contacts, whereas a block in the Rho pathway not only caused a dissolution of focal contacts but also stimulated membrane ruffling and formation of new focal complexes, which were associated with the advance of the cell front.


CONCLUSIONS
Rac functions to signal the creation of new substrate contacts at the cell front, which are associated with the induction of ruffling lamellipodia, whereas Rho serves in the maturation of existing contacts, with both contact types requiring contractility for their formation. The transition from a focal complex to a focal contact is associated with a switch to Rho-kinase dependence. Rac and Rho also influence the development of focal contacts and focal complexes, respectively, through mutually antagonistic pathways.
Rottner
K
K
Institute of Molecular Biology, Austrian Academy of Sciences, A-5020 Salzburg, Billrothstrasse 11, Austria.
Hall
A
A
Small
J V
JV
D016475:3T3 Cells; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D019204:GTP-Binding Proteins / Q000502:physiology*; D020690:GTPase-Activating Proteins; D051379:Mice; D018715:Microscopy, Video; D008954:Models, Biological; D009218:Myosins / Q000502:physiology; D015398:Signal Transduction; D020744:rac GTP-Binding Proteins
D020690:GTPase-Activating Proteins; C085379:rho GTPase-activating protein; D019204:GTP-Binding Proteins; D009218:Myosins; D020744:rac GTP-Binding Proteins