GAS7 coordinates the activity of RAC1 and CDC42 to enhance macropinocytic surveillance and suppress motility in macrophages

Fluid uptake by macropinocytosis is central for the sentinel function of macrophages. However, how the actin network is organized at the cell surface to drive persistent membrane ruffling and macropinocytic cup formation remains unclear. Due to the high curvature of dorsal ruffles, we asked whether membrane curvature-associated proteins, such as those containing F-BAR domains, participate in this process. Here, leveraging public immune transcriptomic profiling and functional assays, we identify Growth Arrest Specific-7 (GAS7) as an F-BAR protein required for membrane ruffling and macropinocytosis in primary human monocyte-derived macrophages. GAS7 is enriched at dorsal ruffles and associates with actin regulators, sustaining high levels of active RAC1, to promote ruffle assembly. Moreover, GAS7 restrains the activation of CDC42, a GTPase linked to filopodia formation, cell motility and invasion. As a result, loss of GAS7 reduces ruffling and fluid uptake and instead promotes a phenotype characterized by increased motility, prominent filopodia, altered podosome dynamics, as well as an extracellular matrix-remodelling transcriptional program. Finally, we demonstrate that GAS7 enhances innate surveillance by augmenting the inflammatory response to muramyl dipeptide (NOD2 ligand) and by modulating the kinetics of TLR4 signalling to lipopolysaccharide. Thus, by coordinating RAC1 and CDC42 activities, GAS7 promotes macropinocytic uptake and enhances the macrophage responsiveness to microbial cues, while suppressing a more motile and invasive program.