Filopodome Mapping Identifies p130Cas as a Mechanosensitive Regulator of Filopodia Stability

Summary Filopodia are adhesive cellular protrusions specialized in the detection of extracellular matrix (ECM)-derived cues. Although ECM engagement at focal adhesions is known to trigger the recruitment of hundreds of proteins (“adhesome”) to fine-tune cellular behavior, the components of the filopodia adhesions remain undefined. Here, we performed a structured-illumination-microscopy-based screen to map the localization of 80 target proteins, linked to cell adhesion and migration, within myosin-X-induced filopodia. We demonstrate preferential enrichment of several adhesion proteins to either filopodia tips, filopodia shafts, or shaft subdomains, suggesting divergent, spatially restricted functions for these proteins. Moreover, proteins with phosphoinositide (PI) binding sites are particularly enriched in filopodia. This, together with the strong localization of PI(3,4)P2 in filopodia tips, predicts critical roles for PIs in regulating filopodia ultra-structure and function. Our mapping further reveals that filopodia adhesions consist of a unique set of proteins, the filopodome, that are distinct from classical nascent adhesions, focal adhesions, and fibrillar adhesions. Using live imaging, we observe that filopodia adhesions can give rise to nascent adhesions, which, in turn, form focal adhesions. We demonstrate that p130Cas (BCAR1) is recruited to filopodia tips via its C-terminal Cas family homology domain (CCHD) and acts as a mechanosensitive regulator of filopodia stability. Finally, we demonstrate that our map based on myosin-X-induced filopodia can be translated to endogenous filopodia and fascin- and IRSp53-mediated filopodia.
Highlights • A super-resolution microscopy screen reveals filopodia core and accessory proteins • FAK and paxillin are accessory, and not core, components of filopodia tip adhesions • PI(3,4)P2 is the prominent phosphatidylinositol species enriched at filopodia tips • p130Cas is a mechanosensitive regulator of filopodia stability
Jacquemet et al. perform super-resolution imaging of filopodia and define a map of core and accessory components based on a pool of target proteins linked to cell adhesion. They show that filopodia adhesions are distinct from classical adhesions and nucleate nascent adhesions and are mechanosensitive, requiring phospho-p130Cas for stabilization.