Filopodome proteomics identifies CCT8 as a MYO10 interactor critical for filopodia functions

Cancer cells utilize filopodia to explore, adhere to, and invade their surrounding microenvironment, yet the protein networks that organize these protrusions remain incompletely defined. To uncover the molecular machinery underlying MYO10-positive filopodia, we targeted the fast biotin ligase TurboID to the filopo-dia tip-localized motor protein MYO10. Proximity biotinylation in two cell types revealed hundreds of potential MYO10 interactors. Surprisingly, there was limited overlap between the cell lines, indicating a previously unknown level of cell-type specificity in filopodia composition. A targeted microscopy and siRNA screen identified MINK1, SCRIB, CSNK1A1, and CCT8 as new regulators of filopodia formation. Focusing on one common interactor between cell lines, CCT8, known as a subunit of the chaperonin TRiC (TCP1 Ring Complex), we found that CCT8 associates with the MYO10 motor domain and regulates MYO10 filopodia independently of TRiC. Depleting CCT8 affected filopodia dynamics and impaired cell spreading, migration, and invasion in breast cancer cells. These findings establish CCT8 as a TRiC-independent regulator of MYO10 filopodia across different cancer cell types, highlight the surprising cell-type-specificity of filopodia composition, and provide a strategy and resource for studying filopodia in various biological contexts.