Figure 6.

Distinct mechanisms for Rac- and Rab5-induced biological responses. The reorganization of the actin cytoskeleton is induced independently by Rac and Rab5. In addition, the Rab5-induced lamellipodia formation and endocytosis may be regulated by distinct mechanisms as well; however, there is a clear relationship between these two events, suggesting that Rab5 may control cytoskeletal reorganization to provide support and direction for the endocytic events. Furthermore, several models have been proposed in which the driving force for cell migration is either a polarized actin polymerization cycle or a polarized endocytic/exocytic cycle. We propose that the dramatic effect of Rab5 on cell migration, which was not observed with Ras or Rac, may be the consequence of the combined action of Rab5-induced actin cytoskeleton reorganization and endocytosis. See DISCUSSION and CONCLUSION for further details.