GPNMB disrupts SNARE complex assembly to maintain bacterial proliferation within macrophages

Xenophagy plays a crucial role in restraining the growth of intracellular bacteria in macrophages. However, the machinery governing autophagosome‒lysosome fusion during bacterial infection remains incompletely understood. Here, we utilize leprosy, an ideal model for exploring the interactions between host defense mechanisms and bacterial infection. We highlight the glycoprotein nonmetastatic melanoma protein B (GPNMB), which is highly expressed in macrophages from lepromatous leprosy (L-Lep) patients and interferes with xenophagy during bacterial infection. Upon infection, GPNMB interacts with autophagosomal-localized STX17, leading to a reduced N-glycosylation level at N296 of GPNMB. This modification promotes the degradation of SNAP29, thus preventing the assembly of the STX17-SNAP29-VAMP8 SNARE complex. Consequently, the fusion of autophagosomes with lysosomes is disrupted, resulting in inhibited cellular autophagic flux. In addition to Mycobacterium leprae, GPNMB deficiency impairs the proliferation of various intracellular bacteria in human macrophages, suggesting a universal role of GPNMB in intracellular bacterial infection. Furthermore, compared with their counterparts, Gpnmbfl/fl Lyz2-Cre mice presented decreased Mycobacterium marinum amplification. Overall, our study reveals a previously unrecognized role of GPNMB in host antibacterial defense and provides insights into its regulatory mechanism in SNARE complex assembly.

Truncated GPNMB, a microglial transmembrane protein, serves as a scavenger receptor for oligomeric β-amyloid peptide1-42 in primary type 1 microglia

Glycoprotein non-metastatic melanoma protein B (GPNMB) is up-regulated in one subtype of microglia (MG) surrounding senile plaque depositions of amyloid-beta (Aβ) peptides. However, whether the microglial GPNMB can recognize the fibrous Aβ peptides as ligands remains unknown. In this study, we report that the truncated form of GPNMB, the antigen for 9F5, serves as a scavenger receptor for oligomeric Aβ1-42 (o-Aβ1-42) in rat primary type 1 MG. 125I-labeled o-Aβ1-42 exhibited specific and saturable endosomal/lysosomal degradation in primary-cultured type 1 MG from GPNMB-expressing wild-type mice, whereas the degradation activity was markedly reduced in cells from Gpnmb-knockout mice. The Gpnmb-siRNA significantly inhibits the degradation of 125I-o-Aβ1-42 by murine microglial MG5 cells. Therefore, GPNMB contributes to mouse MG's o-Aβ1-42 clearance. In rat primary type 1 MG, the cell surface expression of truncated GPNMB was confirmed by a flow cytometric analysis using a previously established 9F5 antibody. 125I-labeled o-Aβ1-42 underwent endosomal/lysosomal degradation by rat primary type 1 MG in a dose-dependent fashion, while the 9F5 antibody inhibited the degradation. The binding of 125I-o-Aβ1-42 to the rat primary type 1 MG was inhibited by 42% by excess unlabeled o-Aβ1-42, and by 52% by the 9F5 antibody. Interestingly, the 125I-o-Aβ1-42 degradations by MG-like cells from human-induced pluripotent stem cells was inhibited by the 9F5 antibody, suggesting that truncated GPNMB also serve as a scavenger receptor for o-Aβ1-42 in human MG. Our study demonstrates that the truncated GPNMB (the antigen for 9F5) binds to oligomeric form of Aβ1-42 and functions as a scavenger receptor on MG, and 9F5 antibody can act as a blocking antibody for the truncated GPNMB.

Emerging roles of MITF as a crucial regulator of immunity

Microphthalmia-associated transcription factor (MITF), a basic helix-loop-helix leucine zipper transcription factor (bHLH-Zip), has been identified as a melanocyte-specific transcription factor and plays a critical role in melanocyte survival, differentiation, function, proliferation and pigmentation. Although numerous studies have explained the roles of MITF in melanocytes and in melanoma development, the function of MITF in the hematopoietic or immune system-beyond its function in melanin-producing cells-is not yet fully understood. However, there is convincing and increasing evidence suggesting that MITF may play multiple important roles in immune-related cells. Therefore, this review is focused on recent advances in elucidating novel functions of MITF in cancer progression and immune responses to cancer. In particular, we highlight the role of MITF as a central modulator in the regulation of immune responses, as elucidated in recent studies.

Soluble DC-HIL/Gpnmb Modulates T-Lymphocyte Extravasation to Inflamed Skin

Previously, we discovered antigen-presenting cells to express DC-HIL receptor and to secrete its soluble form (soluble DC-HIL [sDC-HIL]), both of which bind to syndecan-4 on T cells and endothelial cells (ECs), with the former binding attenuating T-cell function and the latter binding promoting angiogenesis. In this study, we examined the effects of sDC-HIL binding to EC on T-cell extravasation using an allergic contact dermatitis model in mice. The hapten oxazolone applied to ear skin in sensitized mice upregulated cutaneous expression of sDC-HIL, which downregulated the allergic reaction by reducing transendothelial migration of T cells but not other immune cells (neutrophils and mast cells). Moreover, intravenously infused sDC-HIL bound to EC in blood vessels of oxazolone-challenged skin in a scattered and patchy pattern, and intravital microscopic analysis revealed that blood-circulating T cells firmly adhere to DC-HIL-treated endothelia. This regulatory property of sDC-HIL requires syndecan-4 expression by both EC and T cells. Our findings indicate that the DC-HIL/syndecan-4 pathway mediates a cross-talk between T cells and ECs, regulating the cutaneous immune response by preventing extravasation of activated T cells into inflamed skin.

Anti-inflammatory role of Gpnmb in adipose tissue of mice

Obesity can cause a chronic, low-grade inflammation, which is a critical step in the development of type II diabetes and cardiovascular diseases. Inflammation is associated with the expression of glycoprotein nonmetastatic melanoma protein b (Gpnmb), which is mainly expressed by macrophages and dendritic cells. We generated a Gpnmb-knockout mouse line using Crispr-Cas9 to assess the role of Gpnmb in a diet-induced obesity. The absence of Gpnmb did not affect body weight gain and blood lipid parameters. While wildtype animals became obese but remained otherwise metabolically healthy, Gpnmb-knockout animals developed, in addition to obesity, symptoms of metabolic syndrome such as adipose tissue inflammation, insulin resistance and liver fibrosis. We observed a strong Gpnmb expression in adipose tissue macrophages in wildtype animals and a decreased expression of most macrophage-related genes independent of their inflammatory function. This was corroborated by in vitro data showing that Gpnmb was mostly expressed by reparative macrophages while only pro-inflammatory stimuli induced shedding of Gpnmb. The data suggest that Gpnmb is ameliorating adipose tissue inflammation independent of the polarization of macrophages. Taken together, the data suggest an immune-balancing function of Gpnmb that could delay the metabolic damage caused by the induction of obesity.

Glycoprotein nonmetastatic melanoma protein B: A key mediator and an emerging therapeutic target in autoimmune diseases

The glycoprotein nonmetastatic melanoma protein B (GPNMB, also known as osteoactivin) is highly expressed in many cell types and regulates the homeostasis in various tissues. In different physiological contexts, it functions as a melanosome-associated protein, membrane-bound surface receptor, soluble ligand, or adhesion molecule. Therefore, GPNMB is involved in cell differentiation, migration, inflammation, metabolism, and neuroprotection. Because of its various involvement in different physiological conditions, GPNMB has been implicated in many diseases, including cancer, neurological disorders, and more recently immune-mediated diseases. This review summarizes the regulation and function of GPNMB in normal physiology, and discusses the involvement of GPNMB in disease conditions with a particular focus on its potential role and therapeutic implications in autoimmunity.

DC-HIL/Gpnmb Is a Negative Regulator of Tumor Response to Immune Checkpoint Inhibitors

PURPOSE

Immune checkpoint inhibitors (ICI) benefit only a minority of treated patients with cancer. Identification of biomarkers distinguishing responders and nonresponders will improve management of patients with cancer. Because the DC-HIL checkpoint differs from the PD1 pathway in expression and inhibitory mechanisms, we examined whether DC-HIL expression regulates ICI responsiveness.

EXPERIMENTAL DESIGN

Plasma samples were collected from patients with advanced non-small cell lung carcinoma (NSCLC) (n = 76) at baseline and/or follow-up after ICI monotherapy. Blood-soluble DC-HIL (sDC-HIL) was determined and analyzed for correlation with the early tumor response. To study the mechanisms, we measured effect of anti-DC-HIL versus anti-PDL1 mAb on growth of mouse tumor cells in experimentally metastatic lung. Influence of DC-HIL to anti-PDL1 treatment was assessed by changes in tumor response after deletion of host-DC-HIL gene, injection of DC-HIL-expressing myeloid-derived suppressor cells (MDSC), or induction of sDC-HIL expression.

RESULTS

Nonresponders expressed significantly higher levels of baseline sDC-HIL levels than responders. Among patients (n = 28) for fluctuation with time, nonresponders (14/15 cases) showed increasing or persistently elevated levels. Responders (12/13) had decreasing or persistently low levels. Among various tumors, B16 melanoma exhibited resistance to anti-PDL1 but responded to anti-DC-HIL mAb. Using B16 melanoma and LL2 lung cancer, we showed that deletion of host-derived DC-HIL expression converted the resistant tumor to one responsive to anti-PDL1 mAb. The responsive state was reversed by infusion of DC-HIL⁺MDSC or induction of sDC-HIL expression.

CONCLUSIONS

sDC-HIL in the blood and probably DC-HIL receptor expressed by MDSC play an important role in regulating response to ICI in advanced NSCLC.

Blocking Monocytic Myeloid-Derived Suppressor Cell Function via Anti-DC-HIL/GPNMB Antibody Restores the In Vitro Integrity of T Cells from Cancer Patients

PURPOSE

Blocking the function of myeloid-derived suppressor cells (MDSC) is an attractive approach for cancer immunotherapy. Having shown DC-HIL/GPNMB to be the T-cell-inhibitory receptor mediating the suppressor function of MDSCs, we evaluated the potential of anti-DC-HIL mAb as an MDSC-targeting cancer treatment.

EXPERIMENTAL DESIGN

Patients with metastatic cancer (n = 198) were analyzed by flow cytometry for DC-HIL or PDL1 expression on blood CD14+HLA-DRno/lo MDSCs. Their suppressor function was assessed by in vitro coculture with autologous T cells, and the ability of anti-DC-HIL or anti-PDL1 mAb to reverse such function was determined. Tumor expression of these receptors was examined histologically, and the antitumor activity of the mAb was evaluated by attenuated growth of colon cancers in mice.

RESULTS

Patients with metastatic cancer had high blood levels of DC-HIL+ MDSCs compared with healthy controls. Anti-DC-HIL mAb reversed the in vitro function in ∼80% of cancer patients tested, particularly for colon cancer. Despite very low expression on blood MDSCs, anti-PDL1 mAb was as effective as anti-DC-HIL mAb in reversing MDSC function, a paradoxical phenomenon we found to be due to upregulated expression of PDL1 by T-cell-derived IFNγ in cocultures. DC-HIL is not expressed by colorectal cancer cells but by CD14+ cells infiltrating the tumor. Finally, anti-DC-HIL mAb attenuated growth of preestablished colon tumors by reducing MDSCs and increasing IFNγ-secreting T cells in the tumor microenvironment, with similar outcomes to anti-PDL1 mAb.

CONCLUSIONS

Blocking DC-HIL function is a potentially useful treatment for at least colorectal cancer with high blood levels of DC-HIL+ MDSCs.See related commentary by Colombo, p. 453.

Single-walled carbon-nanohorns improve biocompatibility over nanotubes by triggering less protein-initiated pyroptosis and apoptosis in macrophages

Single-walled carbon-nanohorns (SNH) exhibit huge application prospects. Notably, spherical SNH possess different morphology from conventional carbon nanotubes (CNT). However, there is a tremendous lack of studies on the nanotoxicity and mechanism of SNH, and their comparison with nanotubes. Here, the dissimilarity between SNH and CNT is found in many aspects including necrosis, pyroptosis, apoptosis, protein expression, hydrolases leakage, lysosome stress, membrane disturbance and the interaction with membrane proteins. The improved biocompatibility of SNH over four types of established CNT is clearly demonstrated in macrophages. Importantly, a key transmembrane protein, glycoprotein nonmetastatic melanoma protein B (GPNMB) is discovered to initiate the nanotoxicity. Compared to CNT, the weaker nano-GPNMB interaction in SNH group induces lower degree of cascade actions from nano/membrane interplay to final cell hypotoxicity. In conclusion, the geometry of single-construct unit, but not that of dispersive forms or intracellular levels of nanocarbons make the most difference.

Glycoprotein Non-Metastatic Melanoma Protein B (GPNMB) and Cancer: A Novel Potential Therapeutic Target

Glycoprotein non-metastatic melanoma protein B (GPNMB) is a transmembrane protein enriched on the cell surface of cancer cells, including melanoma, glioblastoma, and triple-negative breast cancer. There is growing evidence identifying GPNMB as a tumor-promoter; however, despite its biological and clinical significance, the molecular mechanisms engaged by GPNMB to promote tumorigenesis are not well understood. GPNMB promotes aggressive behaviors such as tumor cell proliferation, migration, and invasion. The extracellular domain of GPNMB shed from the cell surface interacts with integrins to facilitate in the recruitment of immune-suppressive and pro-angiogenic cells to the tumor microenvironment, thereby enhancing tumor migration and invasion. GPNMB also modulates receptor tyrosine kinases and integrin signaling in a cell autonomous fashion, leading to downstream kinase signaling that in turn triggers the expression and secretion of tumorigenic factors such as matrix metalloproteinases (MMPs) and cytokines. Therefore, GPNMB exerts its pro-tumorigenic role both intracellularly and in a paracrine fashion through shedding its extracellular domain. This review highlights the importance of GPNMB in cancer progression and discusses molecular mediators of GPNMB-induced tumor growth and invasion.

Onychomycosis and Chronic Fungal Disease: Exploiting a Commensal Disguise to Stage a Covert Invasion

Onychomycosis is a chronic fungal infection that is recalcitrant to treatment and often results in relapse. New evidence suggests that disease prognosis may be linked to pathogens manipulating host immune responses. Therefore, individuals with specific mutations, including those affecting pattern recognition receptors or the interleukin (IL)-17 and IL-22 pathways, may be more susceptible to infection. Moreover, it is recommended that those with a family history of immune mutations or predisposition to fungal disease be treated aggressively for onychomycosis prior to symptom progression. In addition, incorporating genetic testing and new investigational therapy such as IL-33 and interferon-γ may improve treatment outcome.

Targeting GPNMB with glembatumumab vedotin: Current developments and future opportunities for the treatment of cancer

GPNMB has emerged as an immunomodulator and an important positive mediator of tumor progression and metastasis in numerous solid cancers. Tumor intrinsic GPNMB-mediated effects on cellular signaling, coupled with the ability of GPNMB to influence the primary tumor and metastatic microenvironments in a non-cell autonomous fashion, combine to augment malignant cancer phenotypes. In addition, GPNMB is often overexpressed in a variety of cancers, making it an attractive therapeutic target. In this regard, glembatumumab vedotin, an antibody-drug conjugate (ADC) that targets GPNMB, is currently in clinical trials as a single agent in multiple cancers. In this review, we will describe the physiological functions of GPNMB in normal tissues and summarize the processes through which GPNMB augments tumor growth and metastasis. We will review the pre-clinical and clinical development of glembatumumab vedotin, evaluate on-going clinical trials, explore emerging opportunities for this agent in new disease indications and discuss exciting possibilities for this ADC in the context of combination therapies.

Generation and functional characterization of MDSC-like cells

Myeloid-derived suppressor cells (MDSC) are critical in regulating immune responses by suppressing antigen presenting cells (APC) and T cells. We previously observed that incubation of peripheral blood monocytes with interleukin (IL)-10 during their differentiation to monocyte-derived dendritic cells (moDCs) results in the generation of an APC population with a CD14⁺HLA-DR^lowphenotype (IL-10-APC) with reduced stimulatory capacity similar to human MDSC. Co-incubation experiments now revealed that the addition of IL-10-APC to moDC caused a reduction of DC-induced T-cell proliferation, of the expression of maturation markers, and of secreted cytokines and chemokines such as TNF-α, IL-6, MIP-1α and Rantes. Addition of IL-10-APC increased the immunosuppressive molecule osteoactivin and its corresponding receptor syndecan-4 on moDC. Moreover, CD14⁺HLA-DR^low MDSC isolated from healthy donors expressed high levels of osteoactivin, which was even further upregulated by the auxiliary addition of IL-10. Using transcriptome analysis, we identified a set of molecules and pathways mediating these effects. In addition, we found that IL-10-APC as well as human isolated MDSC expressed higher levels of programmed death (PD)-1, PD-ligand-1 (PD-L1), glucocorticoid-induced-tumor-necrosis-factor-receptor-related-protein (GITR) and GITR-ligand. Inhibition of osteoactivin, syndecan-4, PD-1 or PD-L1 on MDSC by using blocking antibodies restored the stimulatory capacity of DC in co-incubation experiments. Activation of MDSC with Dectin-1 ligand curdlan reduced the expression of osteoactivin and PD-L1. Our results demonstrate that osteoactivin/syndecan-4 and PD-/PD-L1 are key molecules that are profoundly involved in the inhibitory effects of MDSC on DC function and might be promising tools for clinical application.

The Role of Phagocytes and NETs in Dermatophytosis

Innate immunity is the host first line of defense against pathogens. However, only in recent years, we are beginning to better understand the ways it operates. A key player is this branch of the immune response that are the phagocytes, as macrophages, dendritic cells and neutrophils. These cells act as sentinels, employing specialized receptors in the sensing of invaders and host injury, and readily responding to them by production of inflammatory mediators. They afford protection not only by ingesting and destroying pathogens, but also by providing a suitable biochemical environment that shapes the adaptive response. In this review, we aim to present a broad perspective about the role of phagocytes in dermatophytosis, focusing on the mechanisms possibly involved in protective and non-protective responses. A full understanding of how phagocytes fit in the pathogenesis of these infections may open the venue for the development of new and more effective therapeutic approaches.

Immunoresponses in dermatomycoses

Contact with fungal pathogens initiates a series of host responses beginning with innate immunity, which leads to fungal recognition and microbial killing. The innate immune system also modulates the adaptive immune responses, leading to the establishment of immunological memory and protection against pathogens. In the case of dimorphic fungi such as Candida albicans and Malassezia, the immune system plays an important role in tolerance and resistance when managing the organisms either as commensal microbiota or invading pathogens, and disruption of this balance can result in pathological consequences for the host. In addition, Malassezia and dermatophytes have immunomodulatory capabilities that allow them to adapt to their environments and they may exert different effects in healthy and diseased skin. Here, we discuss the host immune responses to dermatomycoses caused by dimorphic fungi such as C. albicans and Malassezia as well as dermatophytes such as Trichophyton spp. and Arthroderma benhamiae to gain a better understanding of the mechanisms of the host-dermatomycosis interaction.

Syndecan-4 as a biomarker to predict clinical outcome for glioblastoma multiforme treated with WT1 peptide vaccine

AIM

In cancer immunotherapy, biomarkers are important for identification of responsive patients. This study was aimed to find biomarkers that predict clinical outcome of WT1 peptide vaccination.

MATERIALS & METHODS

Candidate genes that were expressed differentially between long- and short-term survivors were identified by cDNA microarray analysis of peripheral blood mononuclear cells that were extracted from 30 glioblastoma patients (discovery set) prior to vaccination and validated by quantitative RT-PCR using discovery set and different 23 patients (validation set).

RESULTS

SDC-4 mRNA expression levels distinguished between the long- and short-term survivors: 1-year survival rates were 64.0 and 18.5% in SDC4-low and -high patients, respectively.

CONCLUSION

SDC-4 is a novel predictive biomarker for the efficacy of WT1 peptide vaccine.

Dectin-1 and Dectin-2 promote control of the fungal pathogen Trichophyton rubrum independently of IL-17 and adaptive immunity in experimental deep dermatophytosis

Dermatophytoses are chronic fungal infections, the main causative agent of which is Trichophyton rubrum (T. rubrum). Despite their high occurrence worldwide, the immunological mechanisms underlying these diseases remain largely unknown. Here, we uncovered the C-type lectin receptors, Dectin-1 and Dectin-2, as key elements in the immune response to T. rubrum infection in a model of deep dermatophytosis . In vitro, we observed that deficiency in Dectin-1 and Dectin-2 severely compromised cytokine production by dendritic cells. In vivo, mice lacking Dectin-1 and/or Dectin-2 showed an inadequate pro-inflammatory cytokine production in response to T. rubrum infection, impairing its resolution. Strikingly, neither adaptive immunity nor IL-17 response were required for fungal clearance, highlighting innate immunity as the main checkpoint in the pathogenesis of T. rubrum infection.

GPNMB cooperates with neuropilin-1 to promote mammary tumor growth and engages integrin α5β1 for efficient breast cancer metastasis

Glycoprotein nmb (GPNMB) promotes breast tumor growth and metastasis and its expression in tumor epithelium correlates with poor prognosis in breast cancer patients. Despite its biological and clinical significance, little is known regarding the molecular mechanisms engaged by GPNMB. Herein, we show that GPNMB engages distinct functional domains and mechanisms to promote primary tumor growth and metastasis. We demonstrate that neuropilin-1 (NRP-1) expression is increased in breast cancer cells that overexpress GPNMB. Interestingly, the GPNMB-driven increase in NRP-1 expression potentiated vascular endothelial growth factor signaling in breast cancer cells and was required for the growth, but not metastasis, of these cells in vivo. Interrogation of RNAseq data sets revealed a positive correlation between GPNMB and NRP-1 levels in human breast tumors. Furthermore, we ascribe pro-growth and pro-metastatic functions of GPNMB to its ability to bind α5β1 integrin and increase downstream signaling in breast cancer cells. We show that GPNMB enhances breast cancer cell adhesion to fibronectin, increases α5β1 expression and associates with this receptor through its RGD motif. GPNMB recruitment into integrin complexes activates Src and Fak signaling pathways in an RGD-dependent manner. Importantly, both the RGD motif and cytoplasmic tail of GPNMB are required to promote primary mammary tumor growth; however, only mutation of the RGD motif impaired the formation of lung metastases. Together, these findings identify novel and distinct molecular mediators of GPNMB-induced breast cancer growth and metastasis.

Assessment of the cutaneous immune response during Arthroderma benhamiae and A. vanbreuseghemii infection using an experimental mouse model

BACKGROUND

Dermatophytoses are common but poorly understood skin infections. Most in vivo studies have been performed using the guinea pig as the experimental animal model, which has several limitations.

OBJECTIVES

To develop a mouse model of dermatophytosis suitable for multiple purposes, including the investigation of immunity against dermatophytes.

MATERIALS AND METHODS

Two peculiar fungal species, Arthroderma benhamiae and A. vanbreuseghemii, isolated from tinea in humans having contact with rodents were used for epicutaneous inoculation. During the infection, clinical and histopathological follow-up were performed. The recruitment of immune cells was evaluated by immunofluorescence staining and the levels of cytokine mRNA were quantified by quantitative reverse transcriptase-polymerase chain reaction in the skin of infected mice.

RESULTS

The skin symptoms and microscopic lesions, including the colonization of keratinized epidermal and follicular structures by both dermatophytes, were highly similar to those observed in guinea pig infection models and in natural infections, mimicking acute superficial tinea in humans. The dermal inflammatory cellular infiltrate consisted of macrophages, dendritic cells and especially polymorphonuclear neutrophils, which are one of the histological 'clues' to the diagnosis of dermatophytosis. The in situ cytokine profile was characterized by the overexpression of transforming growth factor-β, interleukin (IL)-1β and IL-6 mRNA during infection, suggesting a role of the T-helper 17 pathway in the establishment of immunity.

CONCLUSIONS

Our new reproducible and validated mouse model of dermatophytosis is a modern in vivo tool that allows a more in-depth understanding of the pathogenesis of human dermatophyte infections.

Lysosomal stress in obese adipose tissue macrophages contributes to MITF-dependent Gpnmb induction

In obesity, adipose tissue (AT) contains crown-like structures where macrophages surround nonviable adipocytes. To understand how AT macrophages (ATMs) contribute to development of insulin resistance, we examined their character in more detail. In silico analysis of F2 mouse populations revealed significant correlation between adipose glycoprotein nonmetastatic melanoma protein B (Gpnmb) expression and body weight. In obese mice and obese individuals, Gpnmb expression was induced in ATMs. Cultured RAW264.7 cells were used to obtain insight into the mechanism of Gpnmb regulation. Gpnmb was potently induced by lysosomal stress inducers, including palmitate and chloroquine, or Torin1, an inhibitor of mammalian target of rapamycin complex 1 (mTORC1). These stimuli also provoked microphthalmia transcription factor (MITF) translocation to the nucleus, and knockdown of MITF by short hairpin RNA indicated its absolute requirement for Gpnmb induction. In agreement with our in vitro data, reduced mTORC1 activity was observed in isolated ATMs from obese mice, which coincided with increased nuclear MITF localization and Gpnmb transcription. Aberrant nutrient sensing provokes lysosomal stress, resulting in attenuated mTORC1 activity and enhanced MITF-dependent Gpnmb induction. Our data identify Gpnmb as a novel marker for obesity-induced ATM infiltration and potentiator of interleukin-4 responses and point toward a crucial role for MITF in driving part of the ATM phenotype.

DC-HIL-expressing myelomonocytic cells are critical promoters of melanoma growth

A major barrier to successful cancer immunotherapy is the tumor’s ability to induce T-cell tolerance by exploiting host regulatory mechanisms. Having discovered the DC-HIL receptor, which inhibits T-cell responses by binding to syndecan-4 on effector T-cells, we posited the DC-HIL/syndecan-4 pathway to play an important role in cancer promotion. Among DC-HIL⁺ myelomonocytic cells, during growth of implanted mouse melanoma, CD11b⁺Gr1⁺ cells were the most expanded population and the most potent at suppressing T-cell activation. Deletion of the DC-HIL gene or infusion of anti-DC-HIL mAb abrogated these cells’ suppressor function and expansion, and markedly diminished melanoma growth and metastasis. IL-1β and IFN-γ were elevated in mice bearing melanoma, and concurrent exposure to both cytokines optimally induced DC-HIL expression by tumor-infiltrating CD11b⁺Gr1⁺ cells. Ligation of DCHIL transduced phosphorylation of its intracellular immunoreceptor tyrosine-based activation motif (ITAM), that in turn induced intracellular expression of IFN-γ and inducible nitric oxide synthase (iNOS), known to mediate T-cell suppression by CD11b⁺Gr1⁺ cells. Thus DC-HIL is the critical mediator of these cells’ suppressor function in melanoma-bearing mice and a potential target for improving melanoma immunotherapy.

The DC-HIL/syndecan-4 pathway regulates autoimmune responses through myeloid-derived suppressor cells

Having discovered that the dendritic cell (DC)-associated heparan sulfate proteoglycan-dependent integrin ligand (DC-HIL) receptor on APCs inhibits T cell activation by binding to syndecan-4 (SD-4) on T cells, we hypothesized that the DC-HIL/SD-4 pathway may regulate autoimmune responses. Using experimental autoimmune encephalomyelitis (EAE) as a disease model, we noted an increase in SD-4(+) T cells in lymphoid organs of wild-type (WT) mice immunized for EAE. The autoimmune disease was also more severely induced (clinically, histologically, and immunophenotypically) in mice knocked out for SD-4 compared with WT cohorts. Moreover, infusion of SD-4(-/-) naive T cells during EAE induction into Rag2(-/-) mice also led to increased severity of EAE in these animals. Similar to SD-4 on T cells, DC-HIL expression was upregulated on myeloid cells during EAE induction, with CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) as the most expanded population and most potent T cell suppressor among the myeloid cells examined. The critical role of DC-HIL was supported by DC-HIL gene deletion or anti-DC-HIL treatment, which abrogated T cell suppressor activity of MDSCs, and also by DC-HIL activation inducing MDSC expression of IFN-γ, NO, and reactive oxygen species. Akin to SD-4(-/-) mice, DC-HIL(-/-) mice manifested exacerbated EAE. Adoptive transfer of MDSCs from EAE-affected WT mice into DC-HIL(-/-) mice reduced EAE severity to the level of EAE-immunized WT mice, an outcome that was precluded by depleting DC-HIL(+) cells from the infused MDSC preparation. Our findings indicate that the DC-HIL/SD-4 pathway regulates autoimmune responses by mediating the T cell suppressor function of MDSCs.

Glycoprotein non-metastatic b (GPNMB): A metastatic mediator and emerging therapeutic target in cancer

Molecularly targeted therapies are rapidly growing with respect to their clinical development and impact on cancer treatment due to their highly selective anti-tumor action. However, many aggressive cancers such as triple-negative breast cancer (TNBC) currently lack well-defined therapeutic targets against which such agents can be developed. The identification of tumor-associated antigens and the generation of antibody drug-conjugates represent an emerging area of intense interest and growth in the field of cancer therapeutics. Glycoprotein non-metastatic b (GPNMB) has recently been identified as a gene that is over-expressed in numerous cancers, including TNBC, and often correlates with the metastatic phenotype. In breast cancer, GPNMB expression in the tumor epithelium is associated with a reduction in disease-free and overall survival. Based on these findings, glembatumumab vedotin (CDX-011), an antibody-drug conjugate that selectively targets GPNMB, is currently being investigated in clinical trials for patients with metastatic breast cancer and unresectable melanoma. This review discusses the physiological and potential pathological roles of GPNMB in normal and cancer tissues, respectively, and details the clinical advances and challenges in targeting GPNMB-expressing malignancies.

The DC-HIL ligand syndecan-4 is a negative regulator of T-cell allo-reactivity responsible for graft-versus-host disease

Acute graft-versus-host disease (GVHD) is the most important cause of mortality after allogeneic haematopoietic stem cell transplantation. Allo-reactive T cells are the major mediators of GVHD and the process is regulated by positive and negative regulators on antigen-presenting cells (APC). Because the significance of negative regulators in GVHD pathogenesis is not fully understood, and having discovered that syndecan-4 (SD-4) on effector T cells mediates the inhibitory function of DC-HIL on APC, we proposed that SD-4 negatively regulates the T-cell response to allo-stimulation in acute GVHD, using SD-4 knockout mice. Although not different from their wild-type counterparts in responsiveness to anti-CD3 stimulation, SD-4(-/-) T cells lost the capacity to mediate the inhibitory function of DC-HIL and were hyper-reactive to allogeneic APC. Moreover, infusion of SD-4(-/-) T cells into sub-lethally γ-irradiated allogeneic mice worsened mortality, with hyper-proliferation of infused T cells in recipients. Although there my be little or no involvement of regulatory T cells in this model because SD-4 deletion had no deleterious effect on T-cell-suppressive activity compared with SD-4(+/+) regulatory T cells. We conclude that SD-4, as the T-cell ligand of DC-HIL, is a potent inhibitor of allo-reactive T cells responsible for GVHD and a potentially useful target for treating this disease.

The Arthroderma benhamiae hydrophobin HypA mediates hydrophobicity and influences recognition by human immune effector cells

Dermatophytes are the most common cause of superficial mycoses in humans and animals. They can coexist with their hosts for many years without causing significant symptoms but also cause highly inflammatory diseases. To identify mechanisms involved in the modulation of the host response during infection caused by the zoophilic dermatophyte Arthroderma benhamiae, cell wall-associated surface proteins were studied. By two-dimensional gel electrophoresis, we found that a hydrophobin protein designated HypA was the dominant cell surface protein. HypA was also detected in the supernatant during the growth and conidiation of the fungus. The A. benhamiae genome harbors only a single hydrophobin gene, designated hypA. A hypA deletion mutant was generated, as was a complemented hypA mutant strain (hypA(C)). In contrast to the wild type and the complemented strain, the hypA deletion mutant exhibited "easily wettable" mycelia and conidia, indicating the loss of surface hydrophobicity of both morphotypes. Compared with the wild type, the hypA deletion mutant triggered an increased activation of human neutrophil granulocytes and dendritic cells, characterized by an increased release of the immune mediators interleukin-6 (IL-6), IL-8, IL-10, and tumor necrosis factor alpha (TNF-α). For the first time, we observed the formation of neutrophil extracellular traps against dermatophytes, whose level of formation was increased by the ΔhypA mutant compared with the wild type. Furthermore, conidia of the ΔhypA strain were killed more effectively by neutrophils. Our data suggest that the recognition of A. benhamiae by the cellular immune defense system is notably influenced by the presence of the surface rodlet layer formed by the hydrophobin HypA.

Pathogenesis of tinea

Dermatophytes are hyphomycetes that can degrade keratin. This puts them in a position to cause infections of the keratin-containing superficial skin. The resulting clinical picture is called tinea. The pathogenesis and course of tinea is decisively determined by pathogen-related factors and by the defense mechanisms of the host. An infection starts with an adherence of fungal propagules, followed by the formation of hyphae that can spread within the tissue. This process is accompanied by a release of fungal enzymes and other pathogenic factors. Next keratinocytes are activated, the epidermal barrier is destroyed, epidermal proliferation is enhanced and defensins are expressed within the epidermis. In addition, innate and specific immune responses are initiated, involving neutrophilic granulocytes, macrophages, antibodies and T cells. The cellular mechanisms are thought to be crucial for healing. Special conditions apply to nail infections, because within nail plates the fungi are not accessible to effective defense mechanisms, as well as to infections of hair follicles that contain specific concentrations of steroid hormones. Dermatophytes that penetrate into the dermis can cause granulomatous inflammatory reactions and systemic immune reactions are supposed to be a trigger of so-called id reactions.