Marc Bernaus-Esqué, Yangjing Liu, Eva Prats, Josep M. Estanyol, Gemma Martin, Maria Calvo, Panagiota Areti Gigourtsi, Mai Khanh Linh Nguyen, Alejandra Álvarez, Silvana Zanlungo, Neus Agell, Albert Lu, Francesc Tebar, Carlos Enrich, Thomas Grewal, Carles Rentero
Annexin A6 (ANXA6) regulates cholesterol transfer across membrane contact sites (MCSs) between late endosomes/lysosomes (LE/Lys) and the endoplasmic reticulum (ER) via the late endosomal StAR-related lipid transfer domain-3 (STARD3) transporter. Here, we describe a significant reduction of MCSs in ANXA6-depleted HeLa cells, which could be rescued by restoration of ANXA6 expression. Using AnxA6 as bait in BioID-based assays, we demonstrate that ANXA6 interacts with various tethers and bona fide MCS proteins that can modulate multi-organelle contacts. STARD3 interactors identified in BioID assays include the mitochondrial translocator protein (TSPO) and myosin heavy chain 9 (MYH9). Strikingly, reduced MCS formation in ANXA6-depleted cells was associated with changes in the STARD3 interactome that indicate altered MCS tethering functions of STARD3. Specifically, ANXA6 deficiency correlated with (1) altered positioning of STARD3-positive LE/Lys; (2) a new repertoire of cortical actin-binding proteins, including myosins interacting with STARD3; (3) and decreased microvillar structures and focal adhesions.