Abstract
To migrate, cells assume a polarized morphology, extending forward with a leading edge with their trailing edge retracting back toward the cell body. Both cell extension and retraction critically depend on the organization and dynamics of the actin cytoskeleton, and the small, monomeric GTPases Rac and Rho are important regulators of actin. Activation of Rac induces actin polymerization and cell extension, whereas activation of Rho enhances acto-myosin II contractility and cell retraction. To coordinate migration, these processes must be carefully regulated. The myosin Myo9b, a Rho GTPase-activating protein (GAP), negatively regulates Rho activity and deletion of Myo9b in leukocytes impairs cell migration through increased Rho activity. However, it is not known whether cell motility is regulated by global or local inhibition of Rho activity by Myo9b. Here, we addressed this question by using Myo9b-deficient macrophage-like cells that expressed different recombinant Myo9b constructs. We found that Myo9b accumulates in lamellipodial extensions generated by Rac-induced actin polymerization as a function of its motor activity. Deletion of Myo9b in HL-60–derived macrophages altered cell morphology and impaired cell migration. Reintroduction of Myo9b or Myo9b motor and GAP mutants revealed that local GAP activity rescues cell morphology and migration. In summary, Rac activation leads to actin polymerization and recruitment of Myo9b, which locally inhibits Rho activity to enhance directional cell migration.
Highlights
We show here that Rac activity is sufficient for Myo9b recruitment to lamellipodial protrusions and that local recruitment of Myo9b RhoGAP activity is important for directional cell migration
Two motor mutants that are defective in either nucleotide binding [21] or hydrolysis [22, 23] were not recruited to the leading edge of protruding lamellipodia and localized comparable to the cytosolic protein mCherry (Fig. 1, A–C). These results show that Rac-induced lamellipodia formation leads to the recruitment of Myo9b and that its motor activity is essential for this purpose
We show that Myo9b controls cell morphology and migration by negatively regulating Rho activity locally at sites of actin polymerization such as at the leading edge of migrating cells
Summary
We show here that Rac activity is sufficient for Myo9b recruitment to lamellipodial protrusions and that local recruitment of Myo9b RhoGAP activity is important for directional cell migration. Cells cotransfected with either mCherry-Myo9bWT or mCherry-Myo9b-R1695M, a mutant lacking RhoGAP activity, showed that both constructs accumulate at the front of those protruding lamellipodia (Fig. 1, A–C). Regulation of HL-60 macrophage morphology and migration by Myo9b requires both its RhoGAP and motor activity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
