Septins as novel regulators of podosome cluster organization and dynamics in human immature dendritic cells

Podosomes are actin-rich adhesions that enable cells to probe their environment, migrate across tissue boundaries, and degrade extracellular matrix. They are often organized in clusters, where their spatial organization is governed by complex actin networks, including a vinculin-associated ventral network and a myosin IIA-associated dorsal network. The molecular composition and mechanisms coordinating these networks, however, remain incompletely understood. Here, we identify septins as novel constituents of the podosome network in human immature dendritic cells. Using super-resolution microscopy, we show that septin 2, 7 and 9 are excluded from the actin core and do not colocalize with the canonical podosome ring. Instead, septins localize to the dorsal actin network that interconnects individual podosomes. Disruption of the septin network does not prevent podosome formation but alters the spatiotemporal organization of the podosome actin network. Furthermore, although septins and myosin IIA do not directly colocalize, septin perturbation leads to axial mislocalization and reduced activity of myosin IIA. Together, our findings identify septins as novel regulators of podosome cluster organization, adding an additional layer of complexity to the cytoskeletal coordination of these structures.