Structural Basis of the LARP4-Filamin A Interaction and Competition with Integrin β7 Tails

Abstract

Filamin A (FLNA) is an actin cross-linking protein that connects multiple transmembrane receptors and cytosolic signaling proteins to regulate cell shape, motility, and signaling. Our previous report has shown that FLNA interacts directly with the La-related protein 4 (LARP4) and this interaction is essential for cell migration. Here, using the x-ray crystallography and protein–protein interaction studies, we investigated the molecular basis of LARP4 binding to FLNA. We described the high-resolution structure of the FLNA immunoglobulin-like repeat 21 (R21) and its complex with the LARP4 peptide. The FLNA-binding site in LARP4 is localized between Ala269 and Asn281, where it forms an extended β strand that interacts with the cleft formed by β strands C and D of FLNA R21. Consistent with this structure, the A279Cfs*2 mutation found in catalogue of somatic mutations in cancer (COSMIC) database and the experimentally introduced F277A mutation both disrupt LARP4 binding to FLNA. In contrast, the COSMIC-listed N275S mutation alters LARP4 membrane localization without affecting FLNA interaction, suggesting distinct functional outcomes. Cell migration assays showed that LARP4-knockdown cells expressing FLNA-binding-deficient mutants migrated faster than those expressing wild-type LARP4. The LARP4-binding site on FLNA overlaps with the β-integrin tail-binding region, and in vitro assays revealed that LARP4 can compete with integrin β7 tails for FLNA R21 binding. These results suggest that the LARP4–FLNA interaction may regulate cell migration, at least in part, by competing with integrin tails, although this mechanism has yet to be confirmed in vivo.