Publications

• SLC15A2 and SLC15A4 mediate the transport of bacterially derived di/tripeptides to enhance the nucleotide-binding oligomerization domain-dependent immune response in mouse bone marrow-derived macrophages.

  Hu Y., Song F., Jiang H., Nunez G., Smith D.E.

  There is increasing evidence that proton-coupled oligopeptide transporters (POTs) can transport bacterially derived chemotactic peptides and therefore reside at the critical interface of innate immune responses and regulation. However, there is substantial contention regarding how these bacterial ... >> More

  There is increasing evidence that proton-coupled oligopeptide transporters (POTs) can transport bacterially derived chemotactic peptides and therefore reside at the critical interface of innate immune responses and regulation. However, there is substantial contention regarding how these bacterial peptides access the cytosol to exert their effects and which POTs are involved in facilitating this process. Thus, the current study proposed to determine the (sub)cellular expression and functional activity of POTs in macrophages derived from mouse bone marrow and to evaluate the effect of specific POT deletion on the production of inflammatory cytokines in wild-type, <i>Pept2</i> knockout and <i>Pht1</i> knockout mice. We found that PEPT2 and PHT1 were highly expressed and functionally active in mouse macrophages, but PEPT1 was absent. The fluorescent imaging of muramyl dipeptide-rhodamine clearly demonstrated that PEPT2 was expressed on the plasma membrane of macrophages, whereas PHT1 was expressed on endosomal membranes. Moreover, both transporters could significantly influence the effect of bacterially derived peptide ligands on cytokine stimulation, as shown by the reduced responses in <i>Pept2</i> knockout and <i>Pht1</i> knockout mice as compared with wild-type animals. Taken as a whole, our results point to PEPT2 (at plasma membranes) and PHT1 (at endosomal membranes) working in concert to optimize the uptake of bacterial ligands into the cytosol of macrophages, thereby enhancing the production of proinflammatory cytokines. This new paradigm offers significant insight into potential drug development strategies along with transporter-targeted therapies for endocrine, inflammatory, and autoimmune diseases. << Less

  J. Immunol. 201:652-662(2018) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Endosomes are specialized platforms for bacterial sensing and NOD2 signalling.

  Nakamura N., Lill J.R., Phung Q., Jiang Z., Bakalarski C., de Maziere A., Klumperman J., Schlatter M., Delamarre L., Mellman I.

  The detection of microbial pathogens involves the recognition of conserved microbial components by host cell sensors such as Toll-like receptors (TLRs) and NOD-like receptors (NLRs). TLRs are membrane receptors that survey the extracellular environment for microbial infections, whereas NLRs are cy ... >> More

  The detection of microbial pathogens involves the recognition of conserved microbial components by host cell sensors such as Toll-like receptors (TLRs) and NOD-like receptors (NLRs). TLRs are membrane receptors that survey the extracellular environment for microbial infections, whereas NLRs are cytosolic complexes that detect microbial products that reach the cytosol. Upon detection, both sensor classes trigger innate inflammatory responses and allow the engagement of adaptive immunity. Endo-lysosomes are the entry sites for a variety of pathogens, and therefore the sites at which the immune system first senses their presence. Pathogens internalized by endocytosis are well known to activate TLRs 3 and 7-9 that are localized to endocytic compartments and detect ligands present in the endosomal lumen. Internalized pathogens also activate sensors in the cytosol such as NOD1 and NOD2 (ref. 2), indicating that endosomes also provide for the translocation of bacterial components across the endosomal membrane. Despite the fact that NOD2 is well understood to have a key role in regulating innate immune responses and that mutations at the NOD2 locus are a common risk factor in inflammatory bowel disease and possibly other chronic inflammatory states, little is known about how its ligands escape from endosomes. Here we show that two endo-lysosomal peptide transporters, SLC15A3 and SLC15A4, are preferentially expressed by dendritic cells, especially after TLR stimulation. The transporters mediate the egress of bacterially derived components, such as the NOD2 cognate ligand muramyl dipeptide (MDP), and are selectively required for NOD2 responses to endosomally derived MDP. Enhanced expression of the transporters also generates endosomal membrane tubules characteristic of dendritic cells, which further enhanced the NOD2-dependent response to MDP. Finally, sensing required the recruitment of NOD2 and its effector kinase RIPK2 (refs 8, 9) to the endosomal membrane, possibly by forming a complex with SLC15A3 or SLC15A4. Thus, dendritic cell endosomes are specialized platforms for both the lumenal and cytosolic sensing of pathogens. << Less

  Nature 509:240-244(2014) [PubMed] [EuropePMC]

• Functional characterization of human peptide/histidine transporter 1 in stably transfected MDCK Cells.

  Song F., Hu Y., Wang Y., Smith D.E., Jiang H.

  The proton-coupled oligopeptide transporter PHT1 (SLC15A4), which facilitates cross-membrane transport of histidine and small peptides from inside the endosomes or lysosomes to cytosol, plays an important role in intracellular peptides homeostasis and innate immune responses. However, it remains a ... >> More

  The proton-coupled oligopeptide transporter PHT1 (SLC15A4), which facilitates cross-membrane transport of histidine and small peptides from inside the endosomes or lysosomes to cytosol, plays an important role in intracellular peptides homeostasis and innate immune responses. However, it remains a challenge to elucidate functional properties of the PHT1 transporter because of its subcellular localization. The purpose of this study was to resort hPHT1 protein from the subcellular to outer cell membrane of MDCK cells stably transfected with human PHT1 mutants, and to characterize its functional activity in these cells. Using this model, the functional activity of hPHT1 was evaluated by cellular uptake studies with d₃-l-histidine, GlySar, and the bacterial peptidoglycan products MDP and Tri-DAP. We found that the disruption of two dileucine motifs was indispensable for hPHT1 transporter being preferentially targeting to plasma membranes. hPHT1 showed high affinity for d₃-l-histidine and low affinity for GlySar, with K_m values of 16.3 ± 1.9 μM and 1.60 ± 0.30 mM, respectively. Moreover, the bacterial peptidoglycan components MDP and Tri-DAP were shown conclusively to be hPHT1 substrates. The uptake of MDP by hPHT1 was inhibited by di/tripeptides and peptide-like drugs, but not by glycine and acyclovir. The functional activity of hPHT1 was also pH-dependent, with an optimal cellular uptake in buffer pH 6.5. Taken together, we established a novel cell model to evaluate the function of hPHT1 in vitro, and confirmed that MDP and Tri-DAP were substrates of hPHT1. Our findings suggest that PHT1 may serve as a potential target for reducing the immune responses and for drug treatment of inflammatory diseases. << Less

  Mol. Pharm. 15:385-393(2018) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• SLC46 Family Transporters Facilitate Cytosolic Innate Immune Recognition of Monomeric Peptidoglycans.

  Paik D., Monahan A., Caffrey D.R., Elling R., Goldman W.E., Silverman N.

  Tracheal cytotoxin (TCT), a monomer of DAP-type peptidoglycan from <i>Bordetella pertussis</i>, causes cytopathology in the respiratory epithelia of mammals and robustly triggers the <i>Drosophila</i> Imd pathway. PGRP-LE, a cytosolic innate immune sensor in <i>Drosophila</i>, directly recognizes ... >> More

  Tracheal cytotoxin (TCT), a monomer of DAP-type peptidoglycan from <i>Bordetella pertussis</i>, causes cytopathology in the respiratory epithelia of mammals and robustly triggers the <i>Drosophila</i> Imd pathway. PGRP-LE, a cytosolic innate immune sensor in <i>Drosophila</i>, directly recognizes TCT and triggers the Imd pathway, yet the mechanisms by which TCT accesses the cytosol are poorly understood. In this study, we report that CG8046, a <i>Drosophila</i> SLC46 family transporter, is a novel transporter facilitating cytosolic recognition of TCT, and plays a crucial role in protecting flies against systemic <i>Escherichia coli</i> infection. In addition, mammalian SLC46A2s promote TCT-triggered NOD1 activation in human epithelial cell lines, indicating that SLC46As is a conserved group of peptidoglycan transporter contributing to cytosolic immune recognition. << Less

  J. Immunol. 199:263-270(2017) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.