Local Myo9b RhoGAP activity regulates cell motility

Cells require precise control of actin cytoskeleton dynamics to migrate effectively. Rac and Rho GTPases are key regulators of actin polymerization and contraction. While Rac promotes cell extension, Rho enhances contractility. These processes must be tightly coordinated for directional movement. Myo9b, a RhoGAP, inhibits Rho activity, but it is unclear whether this inhibition is global or localized. Prior research has shown that Myo9b deletion in leukocytes impairs migration. However, the spatial regulation of Myo9b’s activity remains unexplored. This gap motivated a study to determine if Myo9b acts globally or locally. No prior work had resolved whether Myo9b’s function depends on its localization in lamellipodia. This uncertainty drove the investigation into Myo9b’s role in cell migration. The study aimed to clarify the spatial mechanism of Myo9b’s Rho inhibition. Understanding this could refine models of cell motility regulation.

The study aimed to determine whether Myo9b regulates cell migration through global or local inhibition of Rho activity. Cell migration requires coordinated actin dynamics, and Myo9b is known to inhibit Rho. However, it was unclear whether this inhibition occurs uniformly or in specific regions. The researchers focused on lamellipodial extensions, where Rac activity is high. They hypothesized that Myo9b’s function might be localized to these areas. To test this, they used Myo9b-deficient macrophage-like cells. Reintroducing Myo9b or its mutants allowed them to assess its role in migration. The goal was to clarify whether local Rho inhibition by Myo9b is sufficient for cell motility.

The researchers used Myo9b-deficient macrophage-like cells derived from HL-60 cells. These cells were engineered to express various recombinant Myo9b constructs. The constructs included wild-type Myo9b and mutants lacking motor or GAP activity. Cell morphology and migration were assessed using live-cell imaging. Actin polymerization was monitored in lamellipodia. Myo9b localization was tracked using fluorescent tagging. Rho activity was measured using biosensors. The effects of Myo9b reintroduction were compared to controls. The study combined genetic manipulation with functional assays to determine Myo9b’s role in cell migration.

Myo9b accumulates in lamellipodial extensions driven by Rac-induced actin polymerization. Deletion of Myo9b in HL-60-derived macrophages caused altered morphology and impaired migration. Reintroducing Myo9b rescued both morphology and migration. Myo9b motor mutants failed to localize to lamellipodia but still rescued migration. Myo9b GAP mutants did not rescue migration, indicating that GAP activity is necessary. Local inhibition of Rho by Myo9b is sufficient for directional migration. Myo9b’s localization depends on its motor activity but not on GAP activity. These findings suggest that Myo9b functions locally to regulate Rho activity.

The authors propose that Myo9b regulates cell migration through localized inhibition of Rho activity. Myo9b accumulates in lamellipodia generated by Rac-induced actin polymerization. Local Rho inhibition by Myo9b enhances directional migration. Myo9b’s localization depends on its motor activity but not on GAP activity. Reintroducing Myo9b or motor mutants rescues cell morphology and migration. GAP activity is essential for migration rescue. The study suggests that Myo9b’s function is spatially restricted to lamellipodia. These findings clarify the mechanism of Myo9b’s role in cell motility.