Regulated Assembly of Vacuolar ATPase Is Increased during Cluster Disruption-induced Maturation of Dendritic Cells through a Phosphatidylinositol 3-Kinase/mTOR-dependent Pathway

Background: The V-ATPase is induced to assemble during TLR-activated maturation of dendritic cells. Results: Cluster disruption of dendritic cells also induces V-ATPase assembly by a PI3K/mTOR-dependent mechanism. Conclusion: Semi-mature dendritic cells show increased V-ATPase assembly. Significance: Dendritic cell maturation associated with immune tolerance involves V-ATPase assembly. The vacuolar (H+)-ATPases (V-ATPases) are ATP-driven proton pumps composed of a peripheral V-1 domain and a membrane-embedded V-0 domain. Regulated assembly of V-1 and V-0 represents an important regulatory mechanism for controlling V-ATPase activity in vivo. Previous work has shown that V-ATPase assembly increases during maturation of bone marrow-derived dendritic cells induced by activation of Toll-like receptors. This increased assembly is essential for antigen processing, which is dependent upon an acidic lysosomal pH. Cluster disruption of dendritic cells induces a semi-mature phenotype associated with immune tolerance. Thus, semi-mature dendritic cells are able to process and present self-peptides to suppress autoimmune responses. We have investigated V-ATPase assembly in bone marrow-derived, murine dendritic cells and observed an increase in assembly following cluster disruption. This increased assembly is not dependent upon new protein synthesis and is associated with an increase in concanamycin A-sensitive proton transport in FITC-loaded lysosomes. Inhibition of phosphatidylinositol 3-kinase with wortmannin or mTORC1 with rapamycin effectively inhibits the increased assembly observed upon cluster disruption. These results suggest that the phosphatidylinositol 3-kinase/mTOR pathway is involved in controlling V-ATPase assembly during dendritic cell maturation.