CSF‐1 and PI 3‐kinase regulate podosome distribution and assembly in macrophages

Podosomes are actin-rich adhesive foci found in several cell types, including macrophages. They have a core containing actin and actin-binding proteins and a peripheral ring of integrins and associated proteins. We show that podosomes are abundant in polarized mouse bone marrow-derived macrophages (BMM) and are found primarily in lamellae. We investigated the effects of CSF-1, which induces membrane ruffling, cell spreading, and subsequent polarization and migration, on podosome formation. CSF-1 induces a transient increase in podosome number and enhances the formation of circular arrays of podosomes. Conversely, CSF-1 withdrawal leads to a reduction in podosomes and a decrease in polarized cells. The PI 3-kinase inhibitor LY294002 induces loss of podosomes together with rapid retraction of lamellae and loss of polarity. Our results indicate that CSF-1 acts via PI 3-kinase to enhance podosome assembly and that this is linked to macrophage polarization.