SPG8 spastic paraplegia mutations impair CAV1-integrin-mediated cell adhesion

초록

Mutations in WASHC5/KIAA0196 cause autosomal dominant hereditary spastic paraplegia (HSP), type SPG8. WASHC5 encodes the strumpellin/WASHC5 protein, a core component of the Wiskott-Aldrich syndrome protein and SCAR homologue (WASH) complex that activates actin nucleation at endosomes. Though various cellular roles for strumpellin have been described, how SPG8 mutations lead to HSP remains unclear. Protein interactors of the WASH complex were identified by immunoprecipitation and mass spectrometry. Protein function was assessed in cultured cells using both overexpression and RNAi studies, and cell spreading assays were used to investigate cell adhesion. We uncover cellular changes resulting from pathogenic SPG8 mutations. We identify caveolin-1 (CAV1), a key component of caveolae, as a new interacting protein of strumpellin. RNAi depletion of strumpellin reduces CAV1 protein levels, impairing integrin-mediated cell adhesion. Strumpellin proteins harboring SPG8-associated missense mutations are unable to rescue this defect. SPG8 patient fibroblasts exhibit similar defects in CAV1-integrin-mediated cell adhesion that can be rescued by restoring actin nucleation activity of WASH1 at endosomes. These findings provide a clear molecular link between WASHC5 mutation and CAV1-integrin-mediated cell adhesion, providing important insight into the cellular pathogenesis of SPG8.