Golgi-to-phagosome transport of acid sphingomyelinase and prosaposin is mediated by sortilin

Abstract

SummarySortilin, also known as neurotensin receptor 3 (NTR3), is a transmembrane protein with a dual function. It acts as a receptor for neuromediators and growth factors at the plasma membrane, but it has also been implicated in binding and transport of some lysosomal proteins. However, the role of sortilin during phagosome maturation has not been investigated before. Here, we show that in macrophages, sortilin is mainly localized in the Golgi and transported to latex-bead phagosomes (LBPs). Using live-cell imaging and electron microscopy, we found that sortilin is delivered to LBPs in a manner that depends on its cytoplasmic tail. We also show that sortilin participates in the direct delivery of acid sphingomyelinase (ASM) and prosaposin (PS) to the phagosome, bypassing fusion with lysosomal compartments. Further analysis confirmed that ASM and PS are targeted to the phagosome by sortilin in a Brefeldin-A-sensitive pathway. Analysis of primary macrophages isolated from Sort1 -/-mice indicated that the delivery of ASM and PS, but not pro-cathepsin D, to LBPs was severely impaired. We propose a pathway mediated by sortilin by which selected lysosomal proteins are transported to the phagosome along a Golgi-dependent route during the maturation of phagosomes.

Role of Sortilin in Models of Autoimmune Neuroinflammation

“…Interestingly, loss of sortilin expression reduced the Ag-processing capacity in Sort1 2/2 DCs compared with WT DCs, the most effective APCs. In line with this observation, Wähe et al (19) described that sortilin is involved in the transport of lysosomal proteins in a Golgi-dependent route to phagosomes in macrophages. Upregulation of sortilin in macrophages was also detected during the process of mycobacterial killing (25), emphasizing its role in correct cell function during response to Ags.…”

“…In this context, Herda et al (18) showed that cytotoxic T cells lacking sortilin produce less IFN-g and more granzyme A. In addition, Wähe et al (19) suggested that sortilin transports target proteins to phagosomes in macrophages. Combining sortilin's role as a proneurotrophin receptor in the CNS and its more recently described influence on several immune cell subsets, we were interested in its impact on inflammatory processes in the CNS.…”

Size-dependent mechanism of cargo sorting during lysosome-phagosome fusion is controlled by Rab34

“…RAW 264.7 macrophages were grown in high glucose DMEM with 10% (vol/vol) heat inactivated FCS incubated at 37°C in a 5% (vol/vol) CO 2 atmosphere. BMMs were obtained as described before (40). M. bovis bacillus Calmette-Guérin expressing GFP and DsRed were kind gifts of Brigitte Gicquel (Institute Pasteur, Paris, France).…”

“…Macrophages were pulsed with 1-μm beads and isolated after 15, 30, and 60 min of chase as described before (40).…”

Targeting sortilin in immune cells reduces proinflammatory cytokines and atherosclerosis

“…It is a member of the Vps10p domain receptor family, characterized by a 10-bladed β-propeller that forms a cavity for binding of soluble ligands and a C-terminal cytoplasmic tail that contains sorting motifs responsible for subcellular distribution of the receptors (8)(9)(10). Sortilin exerts diverse cellular functions including intracellular sorting of proteins, such as acid sphingomyelinase, apolipoprotein B100 (apoB100), and PCSK9, as well as engaging in signaling as a coreceptor in cell surface receptor complexes (5)(6)(7)(11)(12)(13). Given the broad functional repertoire of sortilin, we hypothesized that it may affect atherogenesis beyond regulating plasma cholesterol levels.…”