Targeting GL-Lect driven endocytosis to suppress cell plasticity in breast cancer

Abstract Aberrant endocytosis has long been associated with epithelial plasticity and tumorigenesis, but direct in vivo evidence of its causal role in tumor progression and metastasis has been lacking. Here, we identify and molecularly characterize a previously unrecognized form of E-cadherin (ECAD) internalization in mammary epithelial cells. This process is mediated by the endocytic adaptor Epsin 3 (EPN3) through glycolipid-lectin (GL-Lect) driven endocytosis requiring galectin-3 and Eps15-family adaptors. Leveraging an EPN3 knock-in mouse model, we show that dysregulation of GL-Lect driven endocytosis disrupts mammary gland morphogenesis and activates epithelial-to-mesenchymal plasticity (EMP), synergizing with the ERBB2/Neu breast oncogene to drive metastasis. Pharmacologic inhibition of the GL-Lect mechanism suppresses morphogenetic and invasive phenotypes ex vivo, providing proof-of-concept for therapeutic targeting. These findings establish the GL-Lect mechanism as a driver of metastatic plasticity and uncover a tractable vulnerability in BC. Competing Interest Statement UJN and HL are shareholders in Galecto Biotech Inc. The other authors declare no competing interests. Funder Information Declared AIRC, AIRC IG 24415 to SS; AIRC IG 18621 and 5XMille 22759 to GS; AIRC IG 18988, AIRC IG 23060 to PPDF; AIRC IG 15538 and IG 23049, MultiUnit-5×1000 MCO 10.000 to SP European Research Council, ERC-CoG2020 101002280 to SS; ERC-Synergy 101071470-SHAPINCELLFATE to GS The Italian Ministry of University and Scientific Research, PRIN 2022 Prot. 2022W93FTW to SS; PRIN 2020 Prot. 2020R2BP2E, Next Generation EU-CN00000041-National Center for Gene Therapy and Drugs based on RNA Technology to PPDF; PRIN202223GSCIT_01/G53D23002570006/20229RM8A_001, COMBINE/G53D 23007040001/P2022RH4HH002,PNRR_CN3RNA_SPOKE/G43C2200120007 to GS; PRIN 20177E9EPY_002 and MIUR-PRIN 202032AZT3_004 to SP The Italian Ministry of Health, RF-2021-12373957, PNRR-MCNT2-2023-12378490 to PPDF; Ricerca Corrente and 5x1000 funds The University of Milan, PSR-2023 to CT; PSR-2020/2022 to SP Fondazione Umberto Veronesi, FUV to SP Fondation ARC pour la Recherche sur le Cancer, ARCPGA2024110009062_9628 to LJ Mizutani Foundation for Glycoscience, ref. n° 200014 to LJ Agence National de la Recherche, ANR-19-CE13-0001-01, ANR-20-CE15-0009-01, ANR-22-CE11-0030-03, ANR-25-CE11-0988-01 to LJ Fondation pour la Recherche Médicale, EQU202103012926 to LJ FIEO, fellowship to AB