RhoB affects macrophage adhesion, integrin expression and migration

Rho GTPases regulate multiple cellular responses, including cell motility and cell cycle progression. The Rho isoform RhoB represses transformation and affects endosomal trafficking, but its effects on cell adhesion and migration have not been investigated in detail. Here we show that RhoB-null macrophages are more rounded than wild-type macrophages on fibronectin and uncoated glass, and have reduced adhesion to ICAM-1 and glass but not fibronectin. This correlated with lower cell surface expression of beta2 and beta3 integrins but not beta1 integrin. RhoB-null cells migrated faster than Wt cells on fibronectin, consistent with their smaller spread area, but slower than Wt cells on glass, reflecting their reduced adhesion. C3 transferase, which inhibits RhoA, RhoB and RhoC, induced cell spreading but this effect was reduced in RhoB-null cells. However, RhoB is not required for assembly of podosomes, which are integrin-based adhesion sites, whereas C3 transferase induced a decrease in podosomes and defects in tail retraction. Since macrophages do not express RhoC, these effects of C3 transferase are due to inhibition of RhoA rather than RhoB. Our results suggest that RhoB affects cell shape and migration by regulating surface integrin levels.