Atg5/Autophagy inactivation in mouse bone microenvironment promotes tumor development

Bone is an attractive site for cancer colonization, both for primary tumors such as osteosarcoma and for metastases of various malignancies. Preventing bone metastasis, which is associated with a poor prognosis, is a major challenge and identifying the factors involved in skeletal tumoral development is crucial to improve survival. In the present work, we showed that inactivation of the macroautophagy/autophagy-essential gene Atg5 in osteoblasts, the cells in charge of bone formation, stimulates osteosarcoma and breastbone metastasis growth as well as metastatic dissemination. We determined that Atg5 inactivation leads to systemic inflammation and bone proteome modifications including translation downregulation, stress granule formation, and upregulation of fatty acid beta-oxidation. In addition, Atg5 inactivation triggered lysosomal exocytosis through an autophagy-independent effect. Thus, our findings indicated that autophagy/ATG5 deficiency in the bone microenvironment generates a favorable environment for tumor development through several mechanisms and suggested that a bone-targeted autophagy inducer could be used to delay bone metastasis appearance. Abbreviations: ACP5/TRAP : acid phosphatase 5, tartrate resistant; CHI3L1 : chitinase 3 like 1; COL1A1 : collagen type I alpha 1 chain; ECM: extracellular matrix ; FDR: false discovery rate; G3BP1 : G3BP stress granule assembly factor 1; GSEA : gene set enrichment analyses; IFNG : interferon gamma; IL1B : interleukin 1 beta; IL23A : interleukin 23; IPA: ingenuity pathway analyses; ITGAX/CD11c : integrin subunit alpha X; KO : knockout; LAMP1 : lysosomal associated membrane protein 1; LGALS3 : galectin 3; LLOMe : L-leucyl-L-leucine methyl ester; OB : osteoblast; OC : osteoclast; PDCD6IP/Alix : programmed cell death 6 interacting protein; PDK4 : pyruvate dehydrogenase kinase 4.