RNA interference in J774 macrophages reveals a role for coronin 1 in mycobacterial trafficking but not in actin-dependent processes.

Macrophages are crucial for innate immunity, apoptosis, and tissue remodeling, processes that rely on the capacity of macrophages to internalize and process cargo through phagocytosis. Coronin 1, a member of the WD repeat protein family of coronins specifically expressed in leukocytes, was originally identified as a molecule that is recruited to mycobacterial phagosomes and prevents the delivery of mycobacteria to lysosomes, allowing these to survive within phagosomes. However, a role for coronin 1 in mycobacterial pathogenesis has been disputed in favor for its role in mediating phagocytosis and cell motility. In this study, a role for coronin 1 in actin-mediated cellular processes was addressed using RNA interference in the murine macrophage cell line J774. It is shown that the absence of coronin 1 in J774 macrophages expressing small interfering RNA constructs specific for coronin 1 does not affect phagocytosis, macropinocytosis, cell locomotion, or regulation of NADPH oxidase activity. However, in coronin 1-negative J774 cells, internalized mycobacteria were rapidly transferred to lysosomes and killed. Therefore, these results show that in J774 cells coronin 1 has a specific role in modulating phagosome-lysosome transport upon mycobacterial infection and that it is dispensable for most F-actin-mediated cytoskeletal rearrangements.