Brief treatment with transforming growth factor (TGF)–β1 stimulated the migration of macrophages, whereas long-term exposure decreased their migration. Cell migration stimulated by TGF-β1 was markedly inhibited by 10 μg/mL Tat-C3 exoenzyme. TGF-β1 increased mRNA and protein levels of macrophage inflammatory protein (MIP)–1α in the initial period, and these effects also were inhibited by 10 μg/mL Tat-C3 and a dominant-negative (DN)–RhoA (N19RhoA). Cycloheximide, actinomycin D, and antibodies against MIP-1α and monocyte chemoattractant protein-1 (MCP-1) abolished the stimulation of cell migration by TGF-β1. These findings suggest that migration of these cells is regulated directly and indirectly via the expression of chemokines such as MIP-1α and MCP-1 mediated by RhoA in response to TGF-β1. TGF-β1 activated RhoA in the initial period, and thereafter inactivated them, suggesting that the inactivation of RhoA may be the cause of the reduced cell migration in response to TGF-β1 at later times. We therefore attempted to elucidate the molecular mechanism of the inactivation of RhoA by TGF-β1. First, TGF-β1 phosphorylated RhoA via protein kinase A, leading to inactivation of RhoA. Second, wild-type p190 Rho GTPase activating protein (p190RhoGAP) reduced and DN-p190RhoGAP reversed the reduction of cell migration induced by TGF-β, suggesting that it inactivated RhoA via p190 Rho GAP.

Phagocytosis by inflammatory cells is an essential step and a part of innate immunity for protection against foreign pathogens, microorganism or dead cells. Phagocytosis, endocytotic events sequel to binding particle ligands to the specific receptors on phagocyte cell surface such as Fcγ recptor (FcγR), complement receptor (CR), β-glucan receptor, and phosphatidylserine (PS) receptor, require actin assembly, pseudopod extension and phagosome closure. Rho GTPases (RhoA, Cdc42, and Rac1) are critically involved in these processes. Abrupt superoxide formation, called as oxidative burst, occurs through NADPH oxidase complex in leukocytes following phagocytosis. NADPH oxidase complex is composed of membrane proteins, p22(PHOX)and gp91(PHOX), and cytosolic proteins, p40(PHOX), p47(PHOX)and p67(PHOX). The cytosolic subunits and Rac-GTP are translocated to the membrane, forming complete NADPH oxidase complex with membrane part subunits. Binding of imunoglobulin G (IgG)- and complement-opsonized particles to FcγR and CR of leukocytes induces apoptosis of the cells, which may be due to oxidative burst and accompanying cytochrome c release and casapase-3 activation.