Nitric oxide regulates phagocytosis through S-nitrosylation of Rab5.

Phagocytosis is mediated mainly by immune cells, such as macrophages, monocytes, and neutrophils, which clear large pathogens including bacteria. The small GTP-binding protein Rab5 is crucial for both clathrin-dependent endocytosis and phagocytosis, but the role and mechanism of Rab5 activation during phagocytosis are poorly understood. Here, we report that nitric oxide (NO), a novel regulator of Rab5, regulates phagocytosis through S-nitrosylation of Rab5. NO can promote phagocytosis by activating Rab5 in cultured cells, and it potently S-nitrosylates active Rab5 compared to inactive Rab5. Moreover, we demonstrate that two cysteine residues in the C terminus of Rab5 are S-nitrosylated and are important for phagocytosis. Experiments involving mice showed that NO activates Rab5, increases levels of S-nitrosylated Rab5 and is involved in phagocytic bacterial clearance mediated by peritoneal macrophages. Together these data suggest that NO promotes S-nitrosylation of Rab5 to act as a novel Rab5 activator and a key regulator of phagocytosis.