Intracellular osteopontin regulates homeostasis and function of natural killer cells

Osteopontin Regulates Treg Cell Stability and Function with Implications for Anti-Tumor Immunity and Autoimmunity

Foxp3-expressing regulatory T (Treg) cells represent the most highly immunosuppressive cell in the tumor microenvironment (TME) that halts effective anti-tumor immunity. Osteopontin (Opn), an extracellular matrix (ECM) glycophosphoprotein, plays key roles in many types of immune-related diseases and is associated with cancer aggressiveness when expressed by tumor cells. However, its role in Foxp3Treg heterogeneity, function, and stability in the TME is poorly defined. We generated mice with a Foxp3-specific deletion of Opn and assessed the ability of Opn-deficient Tregs to suppress inflammation. As these mice aged, they developed a scurfy-like syndrome characterized by aberrant and excessive activation of effector T cells. We evaluated and further confirmed the reduced suppressive capacity of Opn-deficient Tregs in an in vivo suppression assay of colitis. We also found that mice with Opn-deficient Foxp3+ Tregs have enhanced anti-tumor immunity and reduced tumor burden, associated with an unstable Treg phenotype, paralleled by reduced Foxp3 expression in tumor-infiltrating lymphocytes. Finally, we observed reduced Foxp3 and Helios expression in Opn-deficient Tregs compared to wild-type controls after in vitro activation. Our findings indicate that targeting Opn in Tregs reveals vigorous and effective ways of promoting Treg instability and dysfunction in the TME, facilitating anti-tumor immunity.

Osteopontin: A Novel Therapeutic Target for Respiratory Diseases

Osteopontin (OPN) is a multifunctional phosphorylated protein that is involved in physiological and pathological events. Emerging evidence suggests that OPN also plays a critical role in the pathogenesis of respiratory diseases. OPN can be produced and secreted by various cell types in lungs and overexpression of OPN has been found in acute lung injury/acute respiratory distress syndrome (ALI/ARDS), pulmonary hypertension (PH), pulmonary fibrosis diseases, lung cancer, lung infection, chronic obstructive pulmonary disease (COPD), and asthma. OPN exerts diverse effects on the inflammatory response, immune cell activation, fibrosis and tissue remodeling, and tumorigenesis of these respiratory diseases, and genetic and pharmacological moudulation of OPN exerts therapeutic effects in the treatment of respiratory diseases. In this review, we summarize the recent evidence of multifaceted roles and underlying mechanisms of OPN in these respiratory diseases, and targeting OPN appears to be a potential therapeutic intervention for these diseases.

Immunoregulatory Roles of Osteopontin in Diseases

Osteopontin (OPN) is a multifunctional protein that plays a pivotal role in the immune system. It is involved in various biological processes, including cell adhesion, migration and survival. The study of the immunomodulatory effects of OPN is of paramount importance due to its potential therapeutic applications. A comprehensive understanding of how OPN regulates the immune response could pave the way for the development of novel treatments for a multitude of diseases, including autoimmune disorders, infectious diseases and cancer. Therefore, in the following paper, we provide a systematic overview of OPN and its immunoregulatory roles in various diseases, laying the foundation for the development of OPN-based therapies in the future.

OPN promotes pro-inflammatory cytokine expression via ERK/JNK pathway and M1 macrophage polarization in Rosacea

Rosacea is a chronic inflammatory dermatosis that involves dysregulation of innate and adaptive immune systems. Osteopontin (OPN) is a phosphorylated glycoprotein produced by a broad range of immune cells such as macrophages, keratinocytes, and T cells. However, the role of OPN in rosacea remains to be elucidated. In this study, it was found that OPN expression was significantly upregulated in rosacea patients and LL37-induced rosacea-like skin inflammation. Transcriptome sequencing results indicated that OPN regulated pro-inflammatory cytokines and promoted macrophage polarization towards M1 phenotype in rosacea-like skin inflammation. In vitro, it was demonstrated that intracellular OPN (iOPN) promoted LL37-induced IL1B production through ERK1/2 and JNK pathways in keratinocytes. Moreover, secreted OPN (sOPN) played an important role in keratinocyte-macrophage crosstalk. In conclusion, sOPN and iOPN were identified as key regulators of the innate immune system and played different roles in the pathogenesis of rosacea.

Proteomic profiling identifies SPP1 associated with rapidly progressive interstitial lung disease in anti-MDA5-positive dermatomyositis

BACKGROUND

Anti-melanoma differentiation-associated gene five antibody positive (MDA5+) dermatomyositis (DM) is significantly associated with rapidly progressive interstitial lung disease (RP-ILD). Early detection of RP-ILD remains a major challenge. This study aims to identify and validate prognostic factors for RP-ILD in MDA5+ DM patients.

METHODS

Plasma samples from 20 MDA5+ DM patients and 10 healthy controls (HC) were collected for proteomic analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The proteins of interest were validated in independent samples (20 HC, 20 MDA5+ DM with RP-ILD, and 20 non-RP-ILD patients) with enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 413 differentially expressed proteins (DEPs) were detected between the MDA5+ DM patients and HC. When comparing DEPs between RP-ILD and non-RP-ILD patients, 79 proteins were changed in RP-ILD patients, implicating acute inflammatory response, coagulation, and complement cascades. Six candidate biomarkers were confirmed with ELISA. Secreted phosphoprotein 1 (SPP1), serum amyloid A1 (SAA1), and Kininogen 1 (KNG1) concentrations were significantly elevated in RP-ILD patients than those in non-RP-ILD patients and HC. In the different clinical subgroups, SPP1 was particularly elevated in the high-risk RP-ILD subgroup of MDA5+ DM.

CONCLUSION

This study provides novel insights into the pathogenesis of RP-ILD development in MDA5+ DM and suggests the plasma protein SPP1 could serve as a potential blood biomarker for RP-ILD early warning.

Canonical IRE1 function needed to sustain vigorous natural killer cell proliferation during viral infection

The unfolded protein response (UPR) aims to restore ER homeostasis under conditions of high protein folding load, a function primarily serving secretory cells. Additional, non-canonical UPR functions have recently been unraveled in immune cells. We addressed the function of the inositol-requiring enzyme 1 (IRE1) signaling branch of the UPR in NK cells in homeostasis and microbial challenge. Cell-intrinsic compound deficiency of IRE1 and its downstream transcription factor XBP1 in NKp46+ NK cells, did not affect basal NK cell homeostasis, or overall outcome of viral MCMV infection. However, mixed bone marrow chimeras revealed a competitive advantage in the proliferation of IRE1-sufficient Ly49H+ NK cells after viral infection. CITE-Seq analysis confirmed strong induction of IRE1 early upon infection, concomitant with the activation of a canonical UPR signature. Therefore, we conclude that IRE1/XBP1 activation is required during vigorous NK cell proliferation early upon viral infection, as part of a canonical UPR response.

IL-15 Priming Alters IFN-γ Regulation in Murine NK Cells

NK effector functions can be triggered by inflammatory cytokines and engagement of activating receptors. NK cell production of IFN-γ, an important immunoregulatory cytokine, exhibits activation-specific IFN-γ regulation. Resting murine NK cells exhibit activation-specific metabolic requirements for IFN-γ production, which are reversed for activating receptor-mediated stimulation following IL-15 priming. Although both cytokine and activating receptor stimulation leads to similar IFN-γ protein production, only cytokine stimulation upregulates Ifng transcript, suggesting that protein production is translationally regulated after receptor stimulation. Based on these differences in IFN-γ regulation, we hypothesized that ex vivo IL-15 priming of murine NK cells allows a switch to IFN-γ transcription upon activating receptor engagement. Transcriptional analysis of primed NK cells compared with naive cells or cells cultured with low-dose IL-15 demonstrated that primed cells strongly upregulated Ifng transcript following activating receptor stimulation. This was not due to chromatin accessibility changes in the Ifng locus or changes in ITAM signaling, but was associated with a distinct transcriptional signature induced by ITAM stimulation of primed compared with naive NK cells. Transcriptional analyses identified a common signature of c-Myc (Myc) targets associated with Ifng transcription. Although Myc marked NK cells capable of Ifng transcription, Myc itself was not required for Ifng transcription using a genetic model of Myc deletion. This work highlights altered regulatory networks in IL-15-primed cells, resulting in distinct gene expression patterns and IFN-γ regulation in response to activating receptor stimulation.

Role of osteopontin in cancer development and treatment

Osteopontin (OPN) is a multifunctional protein secreted intracellularly and extracellularly by various cell types, including NK cells, macrophages, osteoblasts, T cells, and cancer cells. Owing to its diverse distribution, OPN plays a role in cell proliferation, stem-cell-like properties, epithelial-mesenchymal transformation, glycolysis, angiogenesis, fibrosis, invasion, and metastasis. In this review, we discuss recent findings, interpret representative studies on OPN expression in cancer, clarify that elevated OPN levels are observed in multiple cancer types (including colorectal, breast, lung, and liver cancer), and explore how OPN-macrophage interactions shape the tumor microenvironment. We also summarize progress in OPN research with regard to tumor therapy, which can facilitate the development of novel anti-tumor treatment strategies.

Osteopontin depletion in macrophages perturbs proteostasis via regulating UCHL1-UPS axis and mitochondria-mediated apoptosis

Introduction

Osteopontin (OPN; also known as SPP1), an immunomodulatory cytokine highly expressed in bone marrow-derived macrophages (BMMΦ), is known to regulate diverse cellular and molecular immune responses. We previously revealed that glatiramer acetate (GA) stimulation of BMMΦ upregulates OPN expression, promoting an anti-inflammatory, pro-healing phenotype, whereas OPN inhibition triggers a pro-inflammatory phenotype. However, the precise role of OPN in macrophage activation state is unknown.

Methods

Here, we applied global proteome profiling via mass spectrometry (MS) analysis to gain a mechanistic understanding of OPN suppression versus induction in primary macrophage cultures. We analyzed protein networks and immune-related functional pathways in BMMΦ either with OPN knockout (OPNKO) or GA-mediated OPN induction compared with wild type (WT) macrophages. The most significant differentially expressed proteins (DEPs) were validated using immunocytochemistry, western blot, and immunoprecipitation assays.

Results and discussion

We identified 631 DEPs in OPNKO or GA-stimulated macrophages as compared to WT macrophages. The two topmost downregulated DEPs in OPNKO macrophages were ubiquitin C-terminal hydrolase L1 (UCHL1), a crucial component of the ubiquitin-proteasome system (UPS), and the anti-inflammatory Heme oxygenase 1 (HMOX-1), whereas GA stimulation upregulated their expression. We found that UCHL1, previously described as a neuron-specific protein, is expressed by BMMΦ and its regulation in macrophages was OPN-dependent. Moreover, UCHL1 interacted with OPN in a protein complex. The effects of GA activation on inducing UCHL1 and anti-inflammatory macrophage profiles were mediated by OPN. Functional pathway analyses revealed two inversely regulated pathways in OPN-deficient macrophages: activated oxidative stress and lysosome-mitochondria-mediated apoptosis (e.g., ROS, Lamp1-2, ATP-synthase subunits, cathepsins, and cytochrome C and B subunits) and inhibited translation and proteolytic pathways (e.g., 60S and 40S ribosomal subunits and UPS proteins). In agreement with the proteome-bioinformatics data, western blot and immunocytochemical analyses revealed that OPN deficiency perturbs protein homeostasis in macrophages-inhibiting translation and protein turnover and inducing apoptosis-whereas OPN induction by GA restores cellular proteostasis. Taken together, OPN is essential for macrophage homeostatic balance via the regulation of protein synthesis, UCHL1-UPS axis, and mitochondria-mediated apoptotic processes, indicating its potential application in immune-based therapies.

IL-15 priming alters IFN-γ regulation in murine NK cells

Natural killer (NK) effector functions can be triggered by inflammatory cytokines and engagement of activating receptors. NK cell production of IFN-γ, an important immunoregulatory cytokine, exhibits activation-specific IFN-γ regulation. Resting murine NK cells exhibit activation-specific metabolic requirements for IFN-γ production, which are reversed for activating receptor-mediated stimulation following IL-15 priming. While both cytokine and activating receptor stimulation leads to similar IFN-γ protein production, only cytokine stimulation upregulates Ifng transcript, suggesting that protein production is translationally regulated after receptor stimulation. Based on these differences in IFN-γ regulation, we hypothesized that ex vivo IL-15 priming of murine NK cells allows a switch to IFN-γ transcription upon activating receptor engagement. Transcriptional analysis of primed NK cells compared to naïve cells or cells cultured with low-dose IL-15 demonstrated that primed cells strongly upregulated Ifng transcript following activating receptor stimulation. This was not due to chromatin accessibility changes in the Ifng locus or changes in ITAM signaling, but was associated with a distinct transcriptional signature induced by ITAM stimulation of primed compared to naïve NK cells. Transcriptional analyses identified a common signature of c-Myc (Myc) targets associated with Ifng transcription. While Myc marked NK cells capable of Ifng transcription, Myc itself was not required for Ifng transcription using a genetic model of Myc deletion. This work highlights altered regulatory networks in IL-15 primed cells, resulting in distinct gene expression patterns and IFN-γ regulation in response to activating receptor stimulation.

Super-enhancer-driven TOX2 mediates oncogenesis in Natural Killer/T Cell Lymphoma

BACKGROUND

Extranodal natural killer/T-cell lymphoma (NKTL) is an aggressive type of non-Hodgkin lymphoma with dismal outcome. A better understanding of disease biology and key oncogenic process is necessary for the development of targeted therapy. Super-enhancers (SEs) have been shown to drive pivotal oncogenes in various malignancies. However, the landscape of SEs and SE-associated oncogenes remain elusive in NKTL.

METHODS

We used Nano-ChIP-seq of the active enhancer marker histone H3 lysine 27 acetylation (H3K27ac) to profile unique SEs NKTL primary tumor samples. Integrative analysis of RNA-seq and survival data further pinned down high value, novel SE oncogenes. We utilized shRNA knockdown, CRISPR-dCas9, luciferase reporter assay, ChIP-PCR to investigate the regulation of transcription factor (TF) on SE oncogenes. Multi-color immunofluorescence (mIF) staining was performed on an independent cohort of clinical samples. Various function experiments were performed to evaluate the effects of TOX2 on the malignancy of NKTL in vitro and in vivo.

RESULTS

SE landscape was substantially different in NKTL samples in comparison with normal tonsils. Several SEs at key transcriptional factor (TF) genes, including TOX2, TBX21(T-bet), EOMES, RUNX2, and ID2, were identified. We confirmed that TOX2 was aberrantly overexpressed in NKTL relative to normal NK cells and high expression of TOX2 was associated with worse survival. Modulation of TOX2 expression by shRNA, CRISPR-dCas9 interference of SE function impacted on cell proliferation, survival and colony formation ability of NKTL cells. Mechanistically, we found that RUNX3 regulates TOX2 transcription by binding to the active elements of its SE. Silencing TOX2 also impaired tumor formation of NKTL cells in vivo. Metastasis-associated phosphatase PRL-3 has been identified and validated as a key downstream effector of TOX2-mediated oncogenesis.

CONCLUSIONS

Our integrative SE profiling strategy revealed the landscape of SEs, novel targets and insights into molecular pathogenesis of NKTL. The RUNX3-TOX2-SE-TOX2-PRL-3 regulatory pathway may represent a hallmark of NKTL biology. Targeting TOX2 could be a valuable therapeutic intervene for NKTL patients and warrants further study in clinic.

Osteopontin (OPN)/SPP1: from its biochemistry to biological functions in the innate immune system and the central nervous system (CNS)

Osteopontin (OPN) is a multifunctional protein, initially identified in osteosarcoma cells with its role of mediating osteoblast adhesion. Later studies revealed that OPN is associated with many inflammatory conditions caused by infections, allergic responses, autoimmunity and tissue damage. Many cell types in the peripheral immune system express OPN with various functions, which could be beneficial or detrimental. Also, more recent studies demonstrated that OPN is highly expressed in the central nervous system (CNS), particularly in microglia during CNS diseases and development. However, understanding of mechanisms underlying OPN's functions in the CNS is still limited. In this review, we focus on peripheral myeloid cells and CNS-resident cells to discuss the expression and functions of OPN.

Perturbomics of tumor-infiltrating NK cells

Natural killer (NK) cells are an innate immune cell type that serves at the first level of defense against pathogens and cancer. NK cells have clinical potential, however, multiple current limitations exist that naturally hinder the successful implementation of NK cell therapy against cancer, including their effector function, persistence, and tumor infiltration. To unbiasedly reveal the functional genetic landscape underlying critical NK cell characteristics against cancer, we perform perturbomics mapping of tumor infiltrating NK cells by joint in vivo AAV-CRISPR screens and single cell sequencing. We establish a strategy with AAV-SleepingBeauty(SB)- CRISPR screening leveraging a custom high-density sgRNA library targeting cell surface genes, and perform four independent in vivo tumor infiltration screens in mouse models of melanoma, breast cancer, pancreatic cancer, and glioblastoma. In parallel, we characterize single-cell transcriptomic landscapes of tumor-infiltrating NK cells, which identifies previously unexplored sub-populations of NK cells with distinct expression profiles, a shift from immature to mature NK (mNK) cells in the tumor microenvironment (TME), and decreased expression of mature marker genes in mNK cells. CALHM2, a calcium homeostasis modulator that emerges from both screen and single cell analyses, shows both in vitro and in vivo efficacy enhancement when perturbed in chimeric antigen receptor (CAR)-NK cells. Differential gene expression analysis reveals that CALHM2 knockout reshapes cytokine production, cell adhesion, and signaling pathways in CAR- NKs. These data directly and systematically map out endogenous factors that naturally limit NK cell function in the TME to offer a broad range of cellular genetic checkpoints as candidates for future engineering to enhance NK cell-based immunotherapies.

Osteopontin and Regulatory T Cells in Effector Phase of Allergic Contact Dermatitis

Studies have shown that osteopontin (OPN) and regulatory T cells play a role in allergic contact dermatitis (ACD), but the mechanisms responsible for their function are poorly understood. The study aimed to determine CD4 T lymphocytes producing intracellular osteopontin (iOPN T cells) and assess the selected T lymphocyte subsets including regulatory T cells in the blood of patients with ACD. Twenty-six patients with a disseminated form of allergic contact dermatitis and 21 healthy controls were enrolled in the study. Blood samples were taken twice: in the acute phase of the disease and during remission. The samples were analyzed by the flow cytometry method. Patients with acute ACD showed significantly higher percentage of iOPN T cells compared with healthy controls which persisted during remission. An increase in the percentage of CD4CD25 and a reduced percentage of regulatory T lymphocytes (CD4CD25highCD127low) were also found in the patients with acute stage of ACD. The percentage of CD4CD25 T lymphocytes showed a positive correlation with the EASI index. The increase in the iOPN T cells can indicate their participation in acute ACD. The decreased percentage of regulatory T lymphocytes in the acute stage of ACD may be related to the transformation of Tregs into CD4CD25 T cells. It may also indicate their increased recruitment to the skin. The positive correlation between the percentage of CD4CD25 lymphocytes and the EASI index may be indirect evidence for the importance of activated lymphocytes-CD4CD25 in addition to CD8 lymphocytes as effector cells in ACD.

The Intracellular and Secreted Sides of Osteopontin and Their Putative Physiopathological Roles

Classically, osteopontin (OPN) has been described as a secreted glycophosprotein. Indeed, most data concerning its physiological and pathological roles are mainly related to the secreted OPN (sOPN). However, there are several instances in which intracellular OPN (iOPN) has been described, presenting some specific roles in distinct experimental models, such as in the immune system, cancer cells, and neurological disorders. We herein aimed to highlight and discuss some of these secreted and intracellular roles of OPN and their putative clinical and biological impacts. Moreover, by consolidating data from the OPN protein database, we also analyzed the occurrence of signal peptide (SP) sequences and putative subcellular localization, especially concerning currently known OPN splicing variants (OPN-SV). Comprehending the roles of OPN in its distinct cellular and tissue environments may provide data regarding the additional applications of this protein as biomarkers and targets for therapeutic purposes, besides further describing its pleiotropic roles.

Osteopontin contributes to virus resistance associated with type I IFN expression, activation of downstream ifn-inducible effector genes, and CCR2+CD115+CD206+ macrophage infiltration following ocular HSV-1 infection of mice

Ocular pathology is often associated with acute herpes simplex virus (HSV)-1 infection of the cornea in mice. The present study was undertaken to determine the role of early T lymphocyte activation 1 protein or osteopontin (OPN) in corneal inflammation and host resistance to ocular HSV-1 infection. C57BL/6 wild type (WT) and osteopontin deficient (OPN KO) mice infected in the cornea with HSV-1 were evaluated for susceptibility to infection and cornea pathology. OPN KO mice were found to possess significantly more infectious virus in the cornea at day 3 and day 7 post infection compared to infected WT mice. Coupled with these findings, HSV-1-infected OPN KO mouse corneas were found to express less interferon (IFN)-α1, double-stranded RNA-dependent protein kinase, and RNase L compared to infected WT animals early post infection that likely contributed to decreased resistance. Notably, OPN KO mice displayed significantly less corneal opacity and neovascularization compared to WT mice that paralleled a decrease in expression of vascular endothelial growth factor (VEGF) A within 12 hr post infection. The change in corneal pathology of the OPN KO mice aligned with a decrease in total leukocyte infiltration into the cornea and specifically, in neutrophils at day 3 post infection and in macrophage subpopulations including CCR2+CD115+CD206+ and CD115+CD183+CD206+ -expressing cells. The infiltration of CD4+ and CD8+ T cells into the cornea was unaltered comparing infected WT to OPN KO mice. Likewise, there was no difference in the total number of HSV-1-specific CD4+ or CD8+ T cells found in the draining lymph node with both sets functionally competent in response to virus antigen comparing WT to OPN KO mice. Collectively, these results demonstrate OPN deficiency directly influences the host innate immune response to ocular HSV-1 infection reducing some aspects of inflammation but at a cost with an increase in local HSV-1 replication.

Interleukin-15 deficient rats have reduced osteopontin at the maternal-fetal interface

Introduction: Uterine Natural Killer (NK) cells are the predominant immune cells within the decidua during early pregnancy. These cells are thought to regulate aspects of decidualization and placental development, but their functions remain poorly characterized, especially in species with deeply invading trophoblasts such as humans and rats. Interleukin-15 (IL-15) is a cytokine required for NK cell development and survival. IL-15 mutant (IL15Δ/Δ) rats lack NK cells and exhibit altered placental development with precocious trophoblast invasion. In this study, we profiled gene expression differences between wild-type and IL15Δ/Δ implantation sites to reveal candidate factors produced by uterine NK cells that may regulate placentation and trophoblast invasion. Methods: Clariom S gene expression profiling was performed using implantation sites collected from pregnant wild-type and IL15Δ/Δ rats on gestational day 9.5. Levels and localization of perforin and osteopontin in implantation sites from wild-type and IL15Δ/Δ rats were further analyzed. The effect of osteopontin on the invasive capacity of rat trophoblasts was evaluated using Matrigel-based Transwell assays. Results: There were 257 genes differentially expressed between wild-type and IL15Δ/Δ implantation sites on gestational day 9.5, including decreased expression of various NK cell markers in IL15Δ/Δ rats, as well as Spp1, which encodes osteopontin. In wild-type rats, osteopontin was present within the decidua basalis and adjacent to the primitive placenta, and osteopontin colocalized with the NK cell marker perforin. Osteopontin was also detectable in uterine glands. Conversely, in IL15Δ/Δ rats, osteopontin and perforin were not readily detectable in the decidua despite robust osteopontin levels in uterine glands. Neutralization of osteopontin in media conditioned by cells isolated from the decidua decreased invasion of rat trophoblasts, suggesting that reduced levels of osteopontin are unlikely to account for the precocious trophoblast invasion in IL15Δ/Δ rats. Conclusion: Osteopontin is expressed by NK cells at the maternal-fetal interface in rats and may contribute to modulation of trophoblast invasion.

Inflammatory-driven NK cell maturation and its impact on pathology

NK cells are innate lymphocytes involved in a large variety of contexts and are crucial in the immunity to intracellular pathogens as well as cancer due to their ability to kill infected or malignant cells. Thus, they harbor a strong potential for clinical and therapeutic use. NK cells do not require antigen exposure to get activated; their functional response is rather based on a balance between inhibitory/activating signals and on the diversity of germline-encoded receptors they express. In order to reach optimal functional status, NK cells go through a step-wise development in the bone marrow before their egress, and dissemination into peripheral organs via the circulation. In this review, we summarize bone marrow NK cell developmental stages and list key factors involved in their differentiation before presenting newly discovered and emerging factors that regulate NK cell central and peripheral maturation. Lastly, we focus on the impact inflammatory contexts themselves can have on NK cell development and functional maturation.

Gene Expression Patterns of Osteopontin Isoforms and Integrins in Malignant Melanoma

Osteopontin (OPN) is a multifunctional glycoprotein that physiologically interacts with different types of integrins. It is considered to be a possible prognostic biomarker in certain tumor types; however, various splicing isoforms exist, which have not been investigated in melanoma. We aimed to define the relative expression pattern of five OPN isoforms and clarify the prognostic significance of the splice variants in melanoma. We also aimed to investigate the expression pattern of eight integrins in the same tumors. Gene expression analyses revealed that the relative expression of OPNa, OPNb, and OPNc is significantly higher in metastatic tumors compared to primary lesions (p < 0.01), whereas the expression of OPN4 and OPN5 was low in both. The more aggressive nodular melanomas had higher expression levels compared to the superficial spreading subtype (p ≤ 0.05). The relative expression of the eight tested integrins was low, with only the expression of ITGB3 being detectable in nodular melanoma (Median_log2 = 1.274). A positive correlation was found between Breslow thickness and the expression of OPNc variant, whereby thicker tumors (>4 mm) had significantly higher expression (p ≤ 0.05). The Breslow thickness was negatively correlated with the expression of OPN4, and similarly with ITGA2. OPNc also exhibited significant positive correlation with the presence of metastasis. Our data show that high expression of OPNa, OPNb, and especially OPNc and low expression of OPN4 and ITGA2 are associated with an advanced stage of tumor progression and poor prognosis in melanoma.

Cell-directed aptamer therapeutic targeting for cancers including those within the central nervous system

Osteopontin (OPN) is produced by tumor cells as well as by myeloid cells and is enriched in the tumor microenvironment (TME) of many cancers. Given the roles of OPN in tumor progression and immune suppression, we hypothesized that targeting OPN with aptamers that have high affinity and specificity could be a promising therapeutic strategy. Bi-specific aptamers targeting ligands for cellular internalization were conjugated to siRNAs to suppress OPN were created, and therapeutic leads were selected based on target engagement and in vivo activity. Aptamers as carriers for siRNA approaches were created including a cancer targeting nucleolin aptamer Ncl-OPN siRNA and a myeloid targeting CpG oligodeoxynucleotide (ODN)-OPN siRNA conjugate. These aptamers were selected as therapeutic leads based on 70–90% OPN inhibition in cancer (GL261, 344SQ, 4T1B2b) and myeloid (DC2.4) cells relative to scramble controls. In established immune competent 344SQ lung cancer and 4T1B2b breast cancer models, these aptamers, including in combination, demonstrate therapeutic activity by inhibiting tumor growth. The Ncl-OPN siRNA aptamer demonstrated efficacy in an immune competent orthotopic glioma model administered systemically secondary to the ability of the aptamer to access the glioma TME. Therapeutic activity was demonstrated using both aptamers in a breast cancer brain metastasis model. Targeted inhibition of OPN in tumor cells and myeloid cells using bifunctional aptamers that are internalized by specific cell types and suppress OPN expression once internalized may have clinical potential in cancer treatment.

Osteopontin aggravates acute lung injury in influenza virus infection by promoting macrophages necroptosis

Infection with influenza A virus (IAV) can trigger pulmonary inflammation and lung damage. Osteopontin (OPN) is an essential regulator of cell death and immunity. However, the role and underlying mechanism of OPN in cell death in IAV-induced pulmonary injury remain poorly understood. Here, we demonstrated that OPN-deficient (OPN^-/-) mice were insensitive to IAV, exhibiting decreased viral loads and attenuated lung injury after IAV infection compared to those in wild-type (WT) mice. Moreover, macrophage necroptosis was significantly reduced in OPN^-/- mice infected with IAV compared to that in infected WT mice. OPN increased the expression of necroptosis-related genes and exacerbated macrophage necroptosis in IAV-infected THP1 cells. Notably, adoptive transfer of WT bone marrow-derived macrophages (BMDMs) or OPN^-/- BMDMs into mice restored resistance to influenza infection, and the rescue effect of OPN^-/- BMDMs was better than that of WT BMDMs. Collectively, these results suggest that OPN deficiency in macrophages reduces necroptosis, which leads to a decrease in viral titers and protects against IAV infection. Therefore, OPN is a potential target for the treatment of IAV infection.

Osteopontin in autoimmune disorders: current knowledge and future perspective

Osteopontin (OPN) is a multifunctional cytokine and adhesion molecule, as well as an unusual regulator for both innate and adaptive immune responses. Several immune cells can produce OPN, including dendritic cells (DCs), macrophages, and T lymphocytes. OPN expression is reported to be increased in a wide range of disorders, including autoimmunity, cancer, and allergy. The overexpression of OPN in several autoimmune disorders, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), Type 1 diabetes (T1D), inflammatory bowel disease (IBD), Sjögren's, and myasthenia gravis, have been shown to be correlated with disease severity. Regarding the important regulatory roles of OPN in the immune system, this study aimed to review the role of this molecule in autoimmune disorders and to provide a complete view of the current knowledge in this field.

Secreted osteopontin from CD4+ T cells limits acute graft-versus-host disease

Osteopontin (OPN) has been considered a potential biomarker of graft-versus-host disease (GVHD). However, the function of OPN in GVHD is still elusive. Using a mouse model of acute GVHD (aGVHD), we report that OPN generated by CD4+ T cells is sufficient to exert a beneficial effect in controlling aGVHD through limiting gastrointestinal pathology, a major target organ of aGVHD. CD4+ T cell-derived OPN works on CD44 expressed in intestinal epithelial cells (IECs) and abates cell death of IECs. OPN also modulates gut microbiota with enhanced health-associated commensal bacteria Akkermansia. Importantly, we use our in vivo mouse mutant model to specifically express OPN isoforms and demonstrate that secreted OPN (sOPN), not intracellular OPN (iOPN), is solely responsible for the protective role of OPN. This study demonstrates that sOPN generated by CD4+ T cells is potent enough to limit aGVHD.

Macrophage-Derived Osteopontin Influences the Amplification of Cryptococcus neoformans-Promoting Type 2 Immune Response

A multifunctional glycoprotein, osteopontin (OPN), can modulate the function of macrophages, resulting in either protective or deleterious effects in various inflammatory diseases and infection in the lungs. Although macrophages play the critical roles in mediating host defenses against cryptococcosis or cryptococcal pathogenesis, the involvement of macrophage-derived OPN in pulmonary infection caused by fungus Cryptococcus has not been elucidated. Thus, our current study aimed to investigate the contribution of OPN to the regulation of host immune response and macrophage function using a mouse model of pulmonary cryptococcosis. We found that OPN was predominantly expressed in alveolar macrophages during C. neoformans infection. Systemic treatment of OPN during C. neoformans infection resulted in an enhanced pulmonary fungal load and an early onset of type 2 inflammation within the lung, as indicated by the increase of pulmonary eosinophil infiltration, type 2 cytokine production, and M2-associated gene expression. Moreover, CRISPR/Cas9-mediated OPN knockout murine macrophages had enhanced ability to clear the intracellular fungus and altered macrophage phenotype from pathogenic M2 to protective M1. Altogether, our data suggested that macrophage-derived OPN contributes to the elaboration of C. neoformans-induced type 2 immune responses and polarization of M2s that promote fungal survival and proliferation within macrophages.

Reliance on Cox10 and oxidative metabolism for antigen-specific NK cell expansion

Natural killer (NK) cell effector functions are dependent on metabolic regulation of cellular function; however, less is known about in vivo metabolic pathways required for NK cell antiviral function. Mice with an inducible NK-specific deletion of Cox10, which encodes a component of electron transport chain complex IV, were generated to investigate the role of oxidative phosphorylation in NK cells during murine cytomegalovirus (MCMV) infection. Ncr1-Cox10Δ/Δ mice had normal numbers of NK cells but impaired expansion of antigen-specific Ly49H+ NK cells and impaired NK cell memory formation. Proliferation in vitro and homeostatic expansion were intact, indicating a specific metabolic requirement for antigen-driven proliferation. Cox10-deficient NK cells upregulated glycolysis, associated with increased AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) activation, although this was insufficient to protect the host. These data demonstrate that oxidative metabolism is required for NK cell antiviral responses in vivo.

Osteopontin and Transplantation: Where Are We Now?

Organ transplantation represents the optimal therapeutic tool for patients with end-stage organ failure. Hematopoietic stem cell transplantation (HSCT) is likewise an effective therapy for a wide range of malignant and non-malignant diseases. Better understanding of transplantation immunology and the use of multi-modal immunosuppression protocols, can decrease the risk of graft failure and graft-versus-host disease (GVHD) after HSCT. Nevertheless, a major challenge of modern transplantology still seems to be finding non-invasive biomarkers for recipients selection, monitoring of allograft function, and diagnosis of rejection. Since proinflammatory cytokine osteopontin (OPN) is closely involved in regulating both adaptive and innate immune responses, as well as the pathogenesis of inflammatory and autoimmune diseases, it is likely to play an important role in organ and HSC transplantation. This review is to summarize recent advances in our knowledge about OPN function in the kidney, heart, liver, lung, and HSC transplantation. Most studies found that elevated OPN is associated with poorer graft function in kidney, heart, liver and lung recipients. Moreover, some reports suggested that this protein can play role in GVHD pathogenesis. However, due to relatively small number of similar studies, as well as some inconclusive results, future investigation in this field is needed to verify if OPN can serve as a biomarker of organ and HSC transplantation. The knowledge about such markers will promote our understanding of the mechanisms underlying graft dysfunction and posttransplant mortality. In addition, such knowledge may be helpful in the development of new treatment strategies and identification of recipients with increased risk of allograft failure.

MicroRNAs as the critical regulators of Doxorubicin resistance in breast tumor cells

BACKGROUND

Chemotherapy is one of the most common treatment options for breast cancer (BC) patients. However, about half of the BC patients are chemotherapeutic resistant. Doxorubicin (DOX) is considered as one of the first line drugs in the treatment of BC patients whose function is negatively affected by multi drug resistance. Due to the severe side effects of DOX, it is very important to diagnose the DOX resistant BC patients. Therefore, assessment of molecular mechanisms involved in DOX resistance can improve the clinical outcomes in BC patients by introducing the novel therapeutic and diagnostic molecular markers. MicroRNAs (miRNAs) as members of the non-coding RNAs family have pivotal roles in various cellular processes including cell proliferation and apoptosis. Therefore, aberrant miRNAs functions and expressions can be associated with tumor progression, metastasis, and drug resistance. Moreover, due to miRNAs stability in body fluids, they can be considered as non-invasive diagnostic markers for the DOX response in BC patients.

MAIN BODY

In the present review, we have summarized all of the miRNAs that have been reported to be associated with DOX resistance in BC for the first time in the world.

CONCLUSIONS

Since, DOX has severe side effects; it is required to distinguish the non DOX-responders from responders to improve the clinical outcomes of BC patients. This review highlights the miRNAs as pivotal regulators of DOX resistance in breast tumor cells. Moreover, the present review paves the way of introducing a non-invasive panel of prediction markers for DOX response among BC patients.

Osteopontin Takes Center Stage in Chronic Liver Disease

Osteopontin (OPN) was first identified in 1986. The prefix osteo- means bone; however, OPN is expressed in other tissues, including liver. The suffix -pontin means bridge and denotes the role of OPN as a link protein within the extracellular matrix. While OPN has well-established physiological roles, multiple "omics" analyses suggest that it is also involved in chronic liver disease. In this review, we provide a summary of the OPN gene and protein structure and regulation. We outline the current knowledge on how OPN is involved in hepatic steatosis in the context of alcoholic liver disease and non-alcoholic fatty liver disease. We describe the mechanisms whereby OPN participates in inflammation and liver fibrosis and discuss current research on its role in hepatocellular carcinoma and cholangiopathies. To conclude, we highlight important points to consider when doing research on OPN and provide direction for making progress on how OPN contributes to chronic liver disease.

A Central Role for Ly49 Receptors in NK Cell Memory

In the past decade, the study of NK cells was transformed by the discovery of three ways these "innate" immune cells display adaptive immune behavior, including the ability to form long-lasting, Ag-specific memories of a wide variety of immunogens. In this review, we examine these types of NK cell memory, highlighting their unique features and underlying similarities. We explore those similarities in depth, focusing on the role that Ly49 receptors play in various types of NK cell memory. From this Ly49 dependency, we will build a model by which we understand the three types of NK cell memory as aspects of what is ultimately the same adaptive immune process, rather than separate facets of NK cell biology. We hope that a defined model for NK cell memory will empower collaboration between researchers of these three fields to further our understanding of this surprising and clinically promising immune response.

The Significance of Secreted Phosphoprotein 1 in Multiple Human Cancers

Malignant tumor represents a major reason for death in the world and its incidence is growing rapidly. Developing the tools for early diagnosis is possibly a promising way to offer diverse therapeutic options and promote the survival chance. Secreted phosphoprotein 1 (SPP1), also called Osteopontin (OPN), has been demonstrated overexpressed in many cancers. However, the specific role of SPP1 in prognosis, gene mutations, and changes in gene and miRNA expression in human cancers is unclear. In this report, we found SPP1 expression was higher in most of the human cancers. Based on Kaplan-Meier plotter and the PrognoScan database, we found high SPP1 expression was significantly correlated with poor survival in various cancers. Using a large dataset of colon adenocarcinoma (COAD), head and neck cancer (HNSC), lung adenocarcinoma (LUAD), and lung squamous cell carcinoma (LUSC) patients from the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases, this study identified 22 common genes and 2 common miRNAs. GO, and KEGG paths analyses suggested that SPP1 correlated genes were mainly involved in positive regulation of immune cell activation and infiltration. SPP1-associated genes and miRNAs regulatory networks suggested that their interactions may play a role in the progression of four selected cancers. SPP1 showed significant positive correlation with the immunocyte and immune marker sets infiltrating degrees. All of these data provide strong evidence that SPP1 may promote tumor progress through interacting with carcinogenic genes and facilitating immune cells’ infiltration in COAD, HNSC, LUAD, and LUSC.

Osteopontin-4 and Osteopontin-5 splice variants are expressed in several tumor cell lines

Among osteopontin splice variants (OPN-SV), the expression profile of osteopontin-4 (OPN4) and osteopontin-5 (OPN5) has not been addressed in distinct cancer types. We herein aimed to investigate their expression in several cancer cell lines, besides comparing it in relation to the three previously described OPN-SV: OPNa, OPNb and OPNc. Total RNA from cancer cell lines, including prostate (PC3 and DU145), ovarian (A2780), breast (MCF-7 and MDA-MB-231), colorectal (Caco-2, HT-29 and HCT-116), thyroid (TT, TPC1 and 8505c) and lung (A549 and NCI-H460) was extracted, followed by cDNA synthesis. OPN-SV transcript analysis by RT-PCR or RT-qPCR were performed using OPN-SV specific oligonucleotides and gapdh and actin transcripts were used as housekeeping controls. OPN4 and OPN5 transcripts displayed co-expression in most tested cell lines. OPN4 was found expressed in similar or higher levels in relation to OPN5. Moreover, in most tested cell lines, OPN4 is also expressed in similar levels to OPNa or OPNb. The expression of OPN5 is also generally variable in relation to the other OPN-SV, but expressed in similar or higher levels in relation to OPNc, depending on each tested cell line. OPN4 and OPN5 seem to be co-expressed in several tumor types and OPN4 is one of the most overexpressed OPN-SV in distinct tumor cell lines. Once both OPN4 and OPN5 are differentially expressed and also evidence tumor-specific expression patterns, we hypothesize that similarly to the other OPN-SV, they also possibly contribute to key aspects of tumor progression, what should be further functionally investigated in distinct tumor models.

Evaluation of Bioactivities of the Bovine Milk Lactoferrin-Osteopontin Complex in Infant Formulas

Human milk contains several bioactive proteins, including lactoferrin (LF) and osteopontin (OPN). These two proteins have been shown to form a complex, which shows increased bioactivities. Bovine LF and OPN can also form such a complex. We assessed bioactivities of the bovine LF-OPN complex (at molar ratios of LF:OPN = 3:1, 5:1, or 8:1) in a formula protein matrix, including LF, OPN, bovine whey protein hydrolysate, and α-lactalbumin. Our results show that the bovine LF-OPN complex together with formula proteins is resistant to in vitro digestion, stimulates intestinal cell proliferation (by 15-50%) and differentiation (by 30-50%), increases antibacterial activity (by 25-50%), and enhances intestinal immunity. The 3:1 ratio of LF to OPN exhibits the most potent effects, as compared with the other two ratios. In conclusion, adding bovine LF and OPN to infant formulas may result in increased stability of the two components and enhanced bioactivities, possibly improving outcomes in formula-fed infants.

Osteopontin and iCD8α Cells Promote Intestinal Intraepithelial Lymphocyte Homeostasis

Intestinal intraepithelial lymphocytes (IEL) comprise a diverse population of cells residing in the epithelium at the interface between the intestinal lumen and the sterile environment of the lamina propria. Because of this anatomical location, IEL are considered critical components of intestinal immune responses. Indeed, IEL are involved in many different immunological processes, ranging from pathogen control to tissue stability. However, despite their critical importance in mucosal immune responses, very little is known about the homeostasis of different IEL subpopulations. The phosphoprotein osteopontin is important for critical physiological processes, including cellular immune responses, such as survival of Th17 cells and homeostasis of NK cells among others. Because of its impact in the immune system, we investigated the role of osteopontin in the homeostasis of IEL. In this study, we report that mice deficient in the expression of osteopontin exhibit reduced numbers of the IEL subpopulations TCRγδ⁺, TCRβ⁺CD4⁺, TCRβ⁺CD4⁺CD8α⁺, and TCRβ⁺CD8αα⁺ cells in comparison with wild-type mice. For some IEL subpopulations, the decrease in cell numbers could be attributed to apoptosis and reduced cell division. Moreover, we show in vitro that exogenous osteopontin stimulates the survival of murine IEL subpopulations and unfractionated IEL derived from human intestines, an effect mediated by CD44, a known osteopontin receptor. We also show that iCD8α IEL but not TCRγδ⁺ IEL, TCRβ⁺ IEL, or intestinal epithelial cells, can promote survival of different IEL populations via osteopontin, indicating an important role for iCD8α cells in the homeostasis of IEL.

NK cells induce hepatic ER stress to promote insulin resistance in obesity through osteopontin production

High-fat diet (HFD) induced hepatic endoplasmic reticulum (ER) stress drives insulin resistance (IR) and steatosis. NK cells in adipose tissue play an important role in the pathogenesis of IR in obesity. Whether NK cells in the liver can induce hepatic ER stress and thus promote IR in obesity is still unknown. We demonstrate that HFD-fed mice display elevated production of proinflammatory cytokine osteopontin (OPN) in hepatic NK cells, especially in CD49a⁺ DX5^- tissue-resident NK (trNK) cells. Obesity-induced ER stress, IR, and steatosis in the liver are ameliorated by ablating NK cells with neutralizing antibody in HFD-fed mice. OPN treatment enhances the expression of ER stress markers, including p-PERK, p-eIF2, ATF4, and CHOP in both murine liver tissues and HL-7702, a human liver cell line. Pretreatment of HL-7702 cells with OPN promotes hyperactivation of JNK and subsequent decrease of tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), resulting in impaired insulin signaling, which can be reversed by inhibiting ER stress. Collectively, we demonstrate that hepatic NK cells induce obesity-induced hepatic ER stress, and IR through OPN production.

Osteopontin as a Link between Inflammation and Cancer: The Thorax in the Spotlight

The glycoprotein osteopontin (OPN) possesses multiple functions in health and disease. To this end, osteopontin has beneficial roles in wound healing, bone homeostasis, and extracellular matrix (ECM) function. On the contrary, osteopontin can be deleterious for the human body during disease. Indeed, osteopontin is a cardinal mediator of tumor-associated inflammation and facilitates metastasis. The purpose of this review is to highlight the importance of osteopontin in malignant processes, focusing on lung and pleural tumors as examples.

Innate CD8αα+ cells promote ILC1-like intraepithelial lymphocyte homeostasis and intestinal inflammation

Innate CD8αα+ cells, also referred to as iCD8α cells, are TCR-negative intraepithelial lymphocytes (IEL) possessing cytokine and chemokine profiles and functions related to innate immune cells. iCD8α cells constitute an important source of osteopontin in the intestinal epithelium. Osteopontin is a pleiotropic cytokine with diverse roles in bone and tissue remodeling, but also has relevant functions in the homeostasis of immune cells. In this report, we present evidence for the role of iCD8α cells in the homeostasis of TCR-negative NKp46+NK1.1+ IEL (ILC1-like). We also show that the effect of iCD8α cells on ILC1-like IEL is enhanced in vitro by osteopontin. We show that in the absence of iCD8α cells, the number of NKp46+NK1.1+ IEL is significantly reduced. These ILC1-like cells are involved in intestinal pathogenesis in the anti-CD40 mouse model of intestinal inflammation. Reduced iCD8α cell numbers results in a milder form of intestinal inflammation in this disease model, whereas treatment with osteopontin increases disease severity. Collectively, our results suggest that iCD8α cells promote survival of NKp46+NK1.1+ IEL, which significantly impacts the development of intestinal inflammation.

Natural Killer Cells and Type 1 Innate Lymphoid Cells Are New Actors in Non-alcoholic Fatty Liver Disease

Obesity and associated liver diseases (Non Alcoholic Fatty Liver Disease, NAFLD) are a major public health problem with increasing incidence in Western countries (25% of the affected population). These complications develop from a fatty liver (steatosis) to an inflammatory state (steatohepatitis) evolving toward fibrosis and hepatocellular carcinoma. Lipid accumulation in the liver contributes to hepatocyte cell death and promotes liver injury. Local immune cells are activated either by Danger Associated Molecular Patterns (DAMPS) released by dead hepatocytes or by bacterial products (PAMPS) reaching the liver due to increased intestinal permeability. The resulting low-grade inflammatory state promotes the progression of liver complications toward more severe grades. Innate lymphoid cells (ILC) are an heterogeneous family of five subsets including circulating Natural Killer (NK) cells, ILC1, ILC2, ILC3, and lymphocytes tissue-inducer cells (LTi). NK cells and tissue-resident ILCs, mainly located at epithelial surfaces, are prompt to rapidly react to environmental changes to mount appropriate immune responses. Recent works have demonstrated the interplay between ILCs subsets and the environment within metabolic active organs such as liver, adipose tissue and gut during diet-induced obesity leading or not to hepatic abnormalities. Here, we provide an overview of the newly roles of NK cells and ILC1 in metabolism focusing on their contribution to the development of NAFLD. We also discuss recent studies that demonstrate the ability of these two subsets to influence tissue-specific metabolism and how their function and homeostasis are affected during metabolic disorders.

Role of osteopontin in dendritic cell shaping of immune responses

Osteopontin (OPN) is a pleiotropic cytokine produced both by immune and non-immune cells and active on different cellular targets. OPN production has been associated with several pathological conditions, including autoimmune diseases (e.g. lupus, multiple sclerosis and rheumatoid arthritis) and cancer. Emerging evidence suggests that the role of OPN has been underestimated, as it seems to be working at multiple levels of immune regulation, such as the shaping of T cell effector responses, the regulation of the tumor microenvironment, and the functional interaction with mesenchymal stromal cells. In this context, dendritic cells (DCs) play a crucial role being both an important source and a cellular target for OPN action. DC family is composed by several cell subsets endowed with specific immune functions. OPN exerts its biological functions through multiple receptors and is produced in different intracellular and secreted forms. OPN production by DC subsets is emerging as a crucial mechanism of regulation in normal and pathological conditions and starts to be exploited as a therapeutic target. This review will focus on the role of DC-derived OPN in shaping immune response and on the complex role of this cytokines in the regulation in immune response.

Is Osteopontin a Friend or Foe of Cell Apoptosis in Inflammatory Gastrointestinal and Liver Diseases?

Osteopontin (OPN) is involved in a variety of biological processes, including bone remodeling, innate immunity, acute and chronic inflammation, and cancer. The expression of OPN occurs in various tissues and cells, including intestinal epithelial cells and immune cells such as macrophages, dendritic cells, and T lymphocytes. OPN plays an important role in the efficient development of T helper 1 immune responses and cell survival by inhibiting apoptosis. The association of OPN with apoptosis has been investigated. In this review, we described the role of OPN in inflammatory gastrointestinal and liver diseases, focusing on the association of OPN with apoptosis. OPN changes its association with apoptosis depending on the type of disease and the phase of disease activity, acting as a promoter or a suppressor of inflammation and inflammatory carcinogenesis. It is essential that the roles of OPN in those diseases are elucidated, and treatments based on its mechanism are developed.

Osteopontin at the Crossroads of Inflammation and Tumor Progression

Complex interactions between tumor and host cells regulate systemic tumor dissemination, a process that begins early at the primary tumor site and goes on until tumor cells detach themselves from the tumor mass and start migrating into the blood or lymphatic vessels. Metastatic cells colonize the target organs and are capable of surviving and growing at distant sites. In this context, osteopontin (OPN) appears to be a key determinant of the crosstalk between cancer cells and the host microenvironment, which in turn modulates immune evasion. OPN is overexpressed in several human carcinomas and has been implicated in inflammation, tumor progression, and metastasis. Thus, it represents one of the most attracting targets for cancer therapy. Within the tumor mass, OPN is secreted in various forms either by the tumor itself or by stroma cells, and it can exert either pro- or antitumorigenic effects according to the cell type and tumor microenvironment. Thus, targeting OPN for therapeutic purposes needs to take into account the heterogeneous functions of the multiple OPN forms with regard to cancer formation and progression. In this review, we will describe the role of systemic, tumor-derived, and stroma-derived OPN, highlighting its pivotal role at the crossroads of inflammation and tumor progression.

Skewing of the population balance of lymphoid and myeloid cells by secreted and intracellular osteopontin

The balance of myeloid populations and lymphoid populations must be well controlled. Here we found that osteopontin (OPN) skewed this balance during pathogenic conditions such as infection and autoimmunity. Notably, two isoforms of OPN exerted distinct effects in shifting this balance through cell-type-specific regulation of apoptosis. Intracellular OPN (iOPN) diminished the population size of myeloid progenitor cells and myeloid cells, and secreted OPN (sOPN) increase the population size of lymphoid cells. The total effect of OPN on skewing the leukocyte population balance was observed as host sensitivity to early systemic infection with Candida albicans and T cell-mediated colitis. Our study suggests previously unknown detrimental roles for two OPN isoforms in causing the imbalance of leukocyte populations.

Modulation of the Intratumoral Immune Landscape by Oncolytic Herpes Simplex Virus Virotherapy

Vaccines and immunotherapeutic approaches to cancers with the advent of immune checkpoint inhibitors and chimeric antigen receptor-modified T cells have recently demonstrated preclinical success and entered clinical trials. Despite advances in these approaches and combinatorial therapeutic regimens, depending on the nature of the cancer and the immune and metabolic landscape within the tumor microenvironment, current immunotherapeutic modalities remain inadequate. Recent clinical trials have demonstrated clear evidence of significant, and sometimes dramatic, antitumor activity, and long-term survival effects of a variety of oncolytic viruses (OVs), particularly oncolytic herpes simplex virus (oHSV). Acting as a multifaceted gene therapy vector and potential adjuvant-like regimens, oHSV can carry genes encoding immunostimulatory molecules in its genome. The oncolytic effect of oHSV and the inflammatory response that the virus stimulates provide a one-two punch at attacking tumors. However, mechanisms underlying oHSV-induced restoration of intratumoral immunosuppression demand extensive research in order to further improve its therapeutic efficacy. In this review, we discuss the current OV-based therapy, with a focus on the unique aspects of oHSV-initiated antiviral and antitumor immune responses, arising from virus-mediated immunological cell death to intratumoral innate and adaptive immunity.

The potential role of Osteopontin in the maintenance of commensal bacteria homeostasis in the intestine

Osteopontin (Opn), a multifunctional extracellular matrix protein, is implicated in the pathogenesis of various inflammatory disorders. Under physiologic conditions, its expression is restricted to certain tissues including bone and kidney tubule. However, cellular activation during disease development induces Opn expression in various immune cells. In this study, using Opn-EGFP knock-in (KI) mice we found that CD8α⁺ T cells in the intestinal tissues, including Peyer’s patch, lamina propria and epithelium, express Opn under steady state conditions. Therefore, we examined the role of Opn-expressing CD8α⁺ T cells in intestinal homeostasis. Interestingly, Opn knockout (KO) mice had altered fecal microflora concordant with a reduction of TCRγδ⁺ intraepithelial lymphocytes (IELs). Consistent with this result, both treatment with anti-Opn blocking antibody and deficiency of Opn resulted in decreased survival of TCRγδ⁺ and TCRαβ⁺ IELs. This data suggests that a possibility that Opn may function as a survival factor for IELs in the intestinal tissue. Collectively, these data suggest the possibility that Opn might regulate the homeostasis of intestinal microflora through maintenance of TCRγδ⁺ IELs, possibly by support of IEL survival.

Embracing the complexity of matricellular proteins: the functional and clinical significance of splice variation

Matricellular proteins influence wide-ranging fundamental cellular processes including cell adhesion, migration, growth and differentiation. They achieve this both through interactions with cell surface receptors and regulation of the matrix environment. Many matricellular proteins are also associated with diverse clinical disorders including cancer and diabetes. Alternative splicing is a precisely regulated process that can produce multiple isoforms with variable functions from a single gene. To date, the expression of alternate transcripts for the matricellular family has been reported for only a handful of genes. Here we analyse the evidence for alternative splicing across the matricellular family including the secreted protein acidic and rich in cysteine (SPARC), thrombospondin, tenascin and CCN families. We find that matricellular proteins have double the average number of splice variants per gene, and discuss the types of domain affected by splicing in matricellular proteins. We also review the clinical significance of alternative splicing for three specific matricellular proteins that have been relatively well characterised: osteopontin (OPN), tenascin-C (TNC) and periostin. Embracing the complexity of matricellular splice variants will be important for understanding the sometimes contradictory function of these powerful regulatory proteins, and for their effective clinical application as biomarkers and therapeutic targets.

Osteopontin has a protective role in prostate tumor development in mice

Osteopontin (OPN) is a protein, generally considered to play a pro-tumorigenic role, whereas several reports have demonstrated the anti-tumorigenic function of OPN during tumor development. These opposing anti- and pro-tumorigenic functions are not fully understood. Here, we report that host-derived OPN plays an anti-tumorigenic role in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model and a TRAMP tumor transplant model. Tumor suppression mediated by OPN in Rag2^-/- mice suggests that OPN is dispensable in the adaptive immune response. We found that host-derived OPN enhanced infiltration of natural killer (NK) cells into TRAMP tumors. The requirement of OPN in NK cell migration towards TRAMP cells was confirmed by an ex vivo cell migration assay. In contrast to TRAMP cells, in vivo B16 tumor development was not inhibited by OPN, and B16 tumors did not show OPN-mediated cell recruitment. It is possible that low levels of chemokine expression by B16 cells do not allow OPN to enhance immune cell recruitment. In addition to demonstrating the anti-tumorigenic role of OPN in TRAMP tumor development, this study also suggests that the contribution of OPN to tumor development depends on the type of tumor as well as the source and isoform of OPN.

Ezh2 regulates differentiation and function of natural killer cells through histone methyltransferase activity

Changes of histone modification status at critical lineage-specifying gene loci in multipotent precursors can influence cell fate commitment. The contribution of these epigenetic mechanisms to natural killer (NK) cell lineage determination from common lymphoid precursors is not understood. Here we investigate the impact of histone methylation repressive marks (H3 Lys27 trimethylation; H3K27(me3)) on early NK cell differentiation. We demonstrate that selective loss of the histone-lysine N-methyltransferase Ezh2 (enhancer of zeste homolog 2) or inhibition of its enzymatic activity with small molecules unexpectedly increased generation of the IL-15 receptor (IL-15R) CD122(+) NK precursors and mature NK progeny from both mouse and human hematopoietic stem and progenitor cells. Mechanistic studies revealed that enhanced NK cell expansion and cytotoxicity against tumor cells were associated with up-regulation of CD122 and the C-type lectin receptor NKG2D. Moreover, NKG2D deficiency diminished the positive effects of Ezh2 inhibitors on NK cell commitment. Identification of the contribution of Ezh2 to NK lineage specification and function reveals an epigenetic-based mechanism that regulates NK cell development and provides insight into the clinical application of Ezh2 inhibitors in NK-based cancer immunotherapies.

Insider trading: Extracellular matrix proteins and their non-canonical intracellular roles

In metazoans, the extracellular matrix (ECM) provides a dynamic, heterogeneous microenvironment that has important supportive and instructive roles. Although the primary site of action of ECM proteins is extracellular, evidence is emerging for non-canonical intracellular roles. Examples include osteopontin, thrombospondins, IGF-binding protein 3 and biglycan, and relate to roles in transcription, cell-stress responses, autophagy and cancer. These findings pose conceptual problems on how proteins signalled for secretion can be routed to the cytosol or nucleus, or can function in environments with diverse redox, pH and ionic conditions. We review evidence for intracellular locations and functions of ECM proteins, and current knowledge of the mechanisms by which they may enter intracellular compartments. We evaluate the experimental methods that are appropriate to obtain rigorous evidence for intracellular localisation and function. Better insight into this under-researched topic is needed to decipher the complete spectrum of physiological and pathological roles of ECM proteins.