CD47-independent effects mediated by the TSP-derived 4N1K peptide

TSP-1-CD47-integrin α4β1 axis drives T cell infiltration and synovial inflammation in rheumatoid arthritis

Background

Immune cell infiltration into joint synovial tissue and promotion of the inflammatory response are important processes in rheumatoid arthritis (RA). This article delves into the crucial role of CD47 in these processes, as well as the mechanisms at both cellular and molecular levels.

Methods

CD47, its ligand TSP-1, and related integrins' expression was analyzed in RA patients' synovial and blood samples vs. normals using GEO data. Additionally, a collagen-induced arthritis (CIA) model using Cd47 knockout rats was employed to explore the significant role of CD47 in the arthritic process. This was further validated in wild-type rat CIA model using CD47 antibodies and inhibitors targeting key enzymes in the CD47-activated integrin α4β1 signaling pathway. The crucial role of CD47 in the CIA model and its way of function were investigated at the animal whole-body level, through various joint section analyses, and at the cellular and molecular level.

Results

Analysis of synovial tissue samples (230 cases) and blood samples (1238 cases) from RA patients in the GEO database showed that the CD47, its ligand TSP-1 and related integrins were significantly overexpressed in RA patients. When Cd47 was knocked out in a rat CIA model, the disease severity of arthritis was significantly alleviated, and the T cell infiltration into rat synovial tissue was remarkably reduced, while the number of B cells, macrophages, and neutrophils did not noticeably change. Mechanistic studies indicated that CD47 on T cells interacts with TSP-1 on vascular endothelial cells in arthritic synovium, activating T cell integrin α4β1. The activated α4β1 binds to VCAM-1, promoting T cell infiltration and inflammatory factor secretion, thereby exacerbating synovial inflammation. The present study also showed that inhibiting the activities of key kinases PKA and Src, through which CD47 mediated integrin α4β1 activation, alleviated arthritis syndromes in CIA rats.

Conclusion

The three-molecule model of "TSP-1, CD47 and integrin α4β1" confirmed that CD47 plays an important role in the occurrence and progression of collagen-induced arthritis, a typical animal model of rheumatoid arthritis. Blocking the TSP-1-CD47 interaction or inhibiting CD47-activated integrin α4β1 on T cells could be a potential therapeutic strategy for rheumatoid arthritis.

Cell autonomous functions of CD47 in regulating cellular plasticity and metabolic plasticity

CD47 is a ubiquitously expressed cell surface receptor, which is widely known for preventing macrophage-mediated phagocytosis by interacting with signal regulatory protein α (SIRPα) on the surface of macrophages. In addition to its role in phagocytosis, emerging studies have reported numerous noncanonical functions of CD47 that include regulation of various cellular processes such as proliferation, migration, apoptosis, differentiation, stress responses, and metabolism. Despite lacking an extensive cytoplasmic signaling domain, CD47 binds to several cytoplasmic proteins, particularly upon engaging with its secreted matricellular ligand, thrombospondin 1. Indeed, the regulatory functions of CD47 are greatly influenced by its interacting partners. These interactions are often cell- and context-specific, adding a further level of complexity. This review addresses the downstream cell-intrinsic signaling pathways regulated by CD47 in various cell types and environments. Some of the key pathways modulated by this receptor include the PI3K/AKT, MAPK/ERK, and nitric oxide signaling pathways, as well as those implicated in glucose, lipid, and mitochondrial metabolism. These pathways play vital roles in maintaining tissue homeostasis, highlighting the importance of understanding the phagocytosis-independent functions of CD47. Given that CD47 expression is dysregulated in a variety of cancers, improving our understanding of the cell-intrinsic signals regulated by this molecule will help advance the development of CD47-targeted therapies.

Progress in cancer research on the regulator of phagocytosis CD47, which determines the fate of tumor cells (Review)

Cluster of differentiation 47 (CD47) is a transmembrane protein that is widely and moderately expressed on the surface of various cells and can have an essential role in mediating cell proliferation, migration, phagocytosis, apoptosis, immune homeostasis and other related responses by binding to its ligands, integrins, thrombospondin-1 and signal regulatory protein α. The poor prognosis of cancer patients is closely associated with high expression of CD47 in glioblastoma, ovarian cancer, breast cancer, bladder cancer, colon cancer and hepatocellular carcinoma. Upregulation of CD47 expression facilitates the growth of numerous types of tumor cells, while downregulation of its expression promotes phagocytosis of tumor cells by macrophages, thereby limiting tumor growth. In addition, blocking CD47 activates the cyclic GMP-AMP (cGAMP) synthase/cGAMP/interferon gene stimulating factor signaling pathway and initiates an adaptive immune response that kills tumor cells. The present review describes the structure, function and interactions of CD47 with its ligands, as well as its regulation of phagocytosis and tumor cell fate. It summarizes the therapeutics, mechanisms of action, research advances and challenges of targeting CD47. In addition, this paper provides an overview of the latest therapeutic options for targeting CD47, such as chimeric antigen receptor (CAR) T-cells, CAR macrophages and nanotechnology-based delivery systems, which are essential for future clinical research on targeting CD47.

Tolerating CD47

Cluster of differentiation 47 (CD47) occupies the outer membrane of human cells, where it binds to soluble and cell surface receptors on the same and other cells, sculpting their topography and resulting in a pleiotropic receptor-multiligand interaction network. It is a focus of drug development to temper and accentuate CD47-driven immune cell liaisons, although consideration of on-target CD47 effects remain neglected. And yet, a late clinical trial of a CD47-blocking antibody was discontinued, existent trials were restrained, and development of CD47-targeting agents halted by some pharmaceutical companies. At this point, if CD47 can be exploited for clinical advantage remains to be determined. Herein an airing is made of the seemingly conflicting actions of CD47 that reflect its position as a junction connecting receptors and signalling pathways that impact numerous human cell types. Prospects of CD47 boosting and blocking are considered along with potential therapeutic implications for autoimmune diseases and cancer.

The role of CD47 in non-neoplastic diseases

CD47 is a 50 kDa five-spanning membrane receptor that plays a crucial role in multiple cellular processes, including myeloid cell activation, neutrophils transmigration, vascular remodeling, leukocyte adhesion and trans-endothelial migration. Recent studies have revealed that CD47 is a highly expressed anti-phagocytic signal in several types of cancer, and therefore, blocking of CD47 has shown an effective therapeutic potential in cancer immunotherapy. In addition, CD47 has been found to be involved in a complex interplay with microglia and other types of cells, and increasing evidence indicates that CD47 can be targeted as part of immune modulatory strategies for non-neoplastic diseases as well. In this review, we focus on CD47 and its role in non-neoplastic diseases, including neurological disorders, atherosclerosis and autoimmune diseases. In addition, we discuss the major challenges and potential remedies associated with CD47-SIRPα-based immunotherapies.

Targeting the CD47/thrombospondin-1 signaling axis regulates immune cell bioenergetics in the tumor microenvironment to potentiate antitumor immune response

BACKGROUND

CD47 is an integral membrane protein that alters adaptive immunosurveillance when bound to the matricellular glycoprotein thrombospondin-1 (TSP1). We examined the impact of the CD47/TSP1 signaling axis on melanoma patient response to anti-PD-1 therapy due to alterations in T cell activation, proliferation, effector function, and bioenergetics.

METHODS

A syngeneic B16 mouse melanoma model was performed to determine if targeting CD47 as monotherapy or in combination with anti-PD-1 impacted tumor burden. Cytotoxic (CD8+) T cells from Pmel-1 transgenic mice were used for T cell activation, cytotoxic T lymphocyte, and cellular bioenergetic assays. Single-cell RNA-sequencing, ELISA, and flow cytometry was performed on peripheral blood mononuclear cells and plasma of melanoma patients receiving anti-PD-1 therapy to examine CD47/TSP1 expression.

RESULTS

Human malignant melanoma tissue had increased CD47 and TSP1 expression within the tumor microenvironment compared with benign tissue. Due to the negative implications CD47/TSP1 can have on antitumor immune responses, we targeted CD47 in a melanoma model and observed a decrease in tumor burden due to increased tumor oxygen saturation and granzyme B secreting CD8+ T cells compared with wild-type tumors. Additionally, Pmel-1 CD8+ T cells exposed to TSP1 had reduced activation, proliferation, and effector function against B16 melanoma cells. Targeting CD47 allowed CD8+ T cells to overcome this TSP1 interaction to sustain these functions. TSP1 exposed CD8+ T cells have a decreased rate of glycolysis; however, targeting CD47 restored glycolysis when CD8+ T cells were exposed to TSP1, suggesting CD47 mediated metabolic reprogramming of T cells. Additionally, non-responding patients to anti-PD-1 therapy had increased T cells expressing CD47 and circulating levels of TSP1 compared with responding patients. Since CD47/TSP1 signaling axis negatively impacts CD8+ T cells and non-responding patients to anti-PD-1 therapy have increased CD47/TSP1 expression, we targeted CD47 in combination with anti-PD-1 in a melanoma model. Targeting CD47 in combination with anti-PD-1 treatment further decreased tumor burden compared with monotherapy and control.

CONCLUSION

CD47/TSP1 expression could serve as a marker to predict patient response to immune checkpoint blockade treatment, and targeting this pathway may preserve T cell activation, proliferation, effector function, and bioenergetics to reduce tumor burden as a monotherapy or in combination with anti-PD-1.

CD47 as a promising therapeutic target in oncology

CD47 is ubiquitously expressed on the surface of cells and plays a critical role in self-recognition. By interacting with SIRPα, TSP-1 and integrins, CD47 modulates cellular phagocytosis by macrophages, determines life span of individual erythrocytes, regulates activation of immune cells, and manipulates synaptic pruning during neuronal development. As such, CD47 has recently be regarded as one of novel innate checkpoint receptor targets for cancer immunotherapy. In this review, we will discuss increasing awareness about the diverse functions of CD47 and its role in immune system homeostasis. Then, we will discuss its potential therapeutic roles against cancer and outlines, the possible future research directions of CD47- based therapeutics against cancer.

Fatty Acids, CD36, Thrombospondin-1, and CD47 in Glioblastoma: Together and/or Separately?

Glioblastoma (GBM) is one of the most aggressive tumors of the central nervous system, characterized by a wide range of inter- and intratumor heterogeneity. Accumulation of fatty acids (FA) metabolites was associated with a low survival rate in high-grade glioma patients. The diversity of brain lipids, especially polyunsaturated fatty acids (PUFAs), is greater than in all other organs and several classes of proteins, such as FA transport proteins (FATPs), and FA translocases are considered principal candidates for PUFAs transport through BBB and delivery of PUFAs to brain cells. Among these, the CD36 FA translocase promotes long-chain FA uptake as well as oxidated lipoproteins. Moreover, CD36 binds and recognizes thrombospondin-1 (TSP-1), an extracellular matrix protein that was shown to play a multifaceted role in cancer as part of the tumor microenvironment. Effects on tumor cells are mediated by TSP-1 through the interaction with CD36 as well as CD47, a member of the immunoglobulin superfamily. TSP-1/CD47 interactions have an important role in the modulation of glioma cell invasion and angiogenesis in GBM. Separately, FA, the two membrane receptors CD36, CD47, and their joint ligand TSP-1 all play a part in GBM pathogenesis. The last research has put in light their interconnection/interrelationship in order to exert a cumulative effect in the modulation of the GBM molecular network.

Novel Pharmaceutical Strategy for Selective Abrogation of TSP1-Induced Vascular Dysfunction by Decoy Recombinant CD47 Soluble Receptor in Prophylaxis and Treatment Models

Elevated thrombospondin 1 (TSP1) is a prevalent factor, via cognate receptor CD47, in the pathogenesis of cardiovascular conditions, including ischemia-reperfusion injury (IRI) and pulmonary arterial hypertension (PAH). Moreover, TSP1/CD47 interaction has been found to be associated with platelet hyperaggregability and impaired nitric oxide response, exacerbating progression in IRI and PAH. Pathological TSP1 in circulation arises as a target of our novel therapeutic approach. Our “proof-of-concept” pharmacological strategy relies on recombinant human CD47 peptide (rh-CD47p) as a decoy receptor protein (DRP) to specifically bind TSP1 and neutralize TSP1-impaired vasorelaxation, strongly implicated in IRI and PAH. The binding of rh-CD47p and TSP1 was first verified as the primary mechanism via Western blotting and further quantified with modified ELISA, which also revealed a linear molar dose-dependent interaction. Ex vivo, pretreatment protocol with rh-CD47p (rh-CD47p added prior to TSP1 incubation) demonstrated a prophylactic effect against TSP1-impairment of endothelium-dependent vasodilation. Post-treatment set-up (TSP1 incubation prior to rh-CD47p addition), mimicking pre-existing excessive TSP1 in PAH, reversed TSP1-inhibited vasodilation back to control level. Dose titration identified an effective molar dose range (approx. ≥1:3 of tTSP1:rh-CD47p) for prevention of/recovery from TSP1-induced vascular dysfunction. Our results indicate the great potential for proposed novel decoy rh-CD47p-therapy to abrogate TSP1-associated cardiovascular complications, such as PAH.

Aging-associated changes in CD47 arrangement and interaction with thrombospondin-1 on red blood cells visualized by super-resolution imaging

CD47 serves as a ligand for signaling regulatory protein α (SIRPα) and as a receptor for thrombospondin-1 (TSP-1). Although CD47, TSP-1, and SIRPα are thought to be involved in the clearance of aged red blood cells (RBCs), aging-associated changes in the expression and interaction of these molecules on RBCs have been elusive. Using direct stochastic optical reconstruction microscopy (dSTORM)-based imaging and quantitative analysis, we can report that CD47 molecules on young RBCs reside as nanoclusters with little binding to TSP-1, suggesting a minimal role for TSP-1/CD47 signaling in normal RBCs. On aged RBCs, CD47 molecules decreased in number but formed bigger and denser clusters, with increased ability to bind TSP-1. Exposure of aged RBCs to TSP-1 resulted in a further increase in the size of CD47 clusters via a lipid raft-dependent mechanism. Furthermore, CD47 cluster formation was dramatically inhibited on thbs1-/- mouse RBCs and associated with a significantly prolonged RBC lifespan. These results indicate that the strength of CD47 binding to its ligand TSP-1 is predominantly determined by the distribution pattern and not the amount of CD47 molecules on RBCs, and offer direct evidence for the role of TSP-1 in phagocytosis of aged RBCs. This study provides clear nanoscale pictures of aging-associated changes in CD47 distribution and TSP-1/CD47 interaction on the cell surface, and insights into the molecular basis for how these molecules coordinate to remove aged RBCs.

CD47 (Cluster of differentiation 47): an anti-phagocytic receptor with a multitude of signaling functions

CD47 is a tumor-associated antigen best known for its ability to bind counter-receptors on the surface of professional phagocytes as an immune-evasion strategy. ⁣Recently, CD47 has been shown to play a role as a signaling receptor, involving a number of cell physiological processes.⁣⁣ This review provides a comprehensive survey of the signaling pathways triggered by CD47 ligand-mediated cell death in tumor cells. Such an understanding should lead to improvement of CD47-targeted anti-tumor therapeutics able to both neutralize the anti-phagocytic role and trigger autonomous tumor cell death.

CD47-ligation induced cell death in T-acute lymphoblastic leukemia

CD47 is a cell-surface marker well recognized for its anti-phagocytic functions. As such, an emerging avenue for targeted cancer therapies involves neutralizing the anti-phagocytic function using monoclonal antibodies (mAbs) to enhance tumour cell immunogenicity. A lesser known consequence of CD47 receptor ligation is the direct induction of tumour cell death. While several mAbs and their derivatives with this property have been studied, the best characterized is the commercially available mAb B6H12, which requires immobilization for induction of cell death. Here, we describe a commercially available mAb, CC2C6, which induces T-cell acute lymphoblastic leukemia (ALL) cell death in soluble form. Soluble CC2C6 induces CD47-dependent cell death in a manner consistent with immobilized B6H12, which is characterized by mitochondrial deficiencies but is independent of caspase activation. Titration studies indicated that CC2C6 shares a common CD47-epitope with B6H12. Importantly, CC2C6 retains the anti-phagocytic neutralizing function, thus possessing dual anti-tumour properties. Although CD47-ligation induced cell death occurs in a caspase-independent manner, CC2C6 was found to stimulate increases in Mcl-1 and NOXA levels, two Bcl-2 family proteins that govern the intrinsic apoptosis pathway. Further analysis revealed that the ratio of Mcl-1:NOXA were minimally altered for cells treated with CC2C6, in comparison to cells treated with agents that induced caspase-dependent apoptosis which alter this ratio in favour of NOXA. Finally, we found that CC2C6 can synergize with low dose chemotherapeutic agents that induce classical apoptosis, giving rise to the possibility of an effective combination treatment with reduced long-term sequelae associated with high-dose chemotherapies in childhood ALL.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

T-cell regulation through a basic suppressive mechanism targeting low-density lipoprotein receptor-related protein 1

Cell adhesion is generally considered to depend on positive regulation through ligation of integrins and cytokine receptors. However, here we show that T-cell adhesion, and notably also T-cell receptor (TCR) -induced activation, are subject to constant suppression through shedding of low-density lipoprotein receptor-related protein 1 (LRP1). The broad-spectrum metalloprotease inhibitor GM6001 abrogated shedding, so inducing prominent cell surface expression of LRP1 while enhancing TCR-induced activation and adhesion to β₁ and β₂ integrin ligands, hence arresting the cells. Integrin ligands also inhibited shedding but the effect was less potent than that of GM6001. Unlike GM6001, integrin ligands also induced cell surface expression of full-length thrombospondin-1 (TSP170) and TSP130, which associated with LRP1, and TSP110, which did not associate with LRP1. Cell surface expression of LRP1 and TSP130 were induced exclusively in adhering cells, expression of TSP110 preferentially in non-adhering cells and expression of TSP170 correlated with T-cell motility. The pro-adhesive chemokine CXCL12 also inhibited LRP1 shedding and induced surface expression of TSP170 and TSP130 while inhibiting TSP110. Exogenous TSP-1 and ligation of CD28 inhibited shedding although less effectively than GM6001, and the inhibition through CD28 was independent of TSP-1. Small interfering RNA silencing experiments confirmed involvement of LRP1 and TSP-1 in integrin-dependent adhesion and TCR-induced activation. Hence, the poor LRP1 expression in T cells depends on shedding. Integrin ligands and CXCL12 antagonize shedding through a TSP-1-dependent pathway and ligation of CD28 antagonizes shedding independent of TSP-1. The disappearance of LRP1 from the cell surface may provide basic immunosuppression at the T-cell level.

Anti-CD47 antibodies induce phagocytosis of live, malignant B cells by macrophages via the Fc domain, resulting in cell death by phagoptosis

When expressed on the surface of cells, CD47 inhibits phagocytosis of these cells by phagocytes. Most human cancers overexpress CD47, and antibodies to CD47 have shown a remarkable ability to clear a range of cancers in animal models. However, the mechanism by which these antibodies cause cancer cell death is unclear. We find that CD47 is expressed on the surface of three B-cell lines from human malignancies: 697 (pre-B-ALL lymphoblasts), Ramos and DG-75 (both mature B-cells, Burkitt’s lymphoma), and anti-CD47 antibodies greatly increase the phagocytosis of all three cell line by macrophages. In the presence of macrophages, the antibodies cause clearance of the lymphoblasts within hours, but in the absence of macrophages, the antibodies have no effect on lymphoblast viability. Macrophages engulf viable lymphoblasts containing mitochondria with a normal membrane potential, but following engulfment the mitochondrial membrane potential is lost indicating a loss of viability. Inhibition of phagocytosis protects lymphoblasts from death indicating that phagocytosis is required for anti-CD47 mediated cell death. Blocking either the antibody Fc domain or Fc receptors inhibits antibody-induced phagocytosis. Antibodies against cell surface markers CD10 or CD19 also induced Fc-domain-dependent phagocytosis, but at a lower level commensurate with expression. Thus, phagoptosis may contribute to the efficacy of a number of therapeutic antibodies used in cancer therapy, as well as potentially endogenous antibodies. We conclude that anti-CD47 antibodies induce phagocytosis by binding CD47 on lymphoblast and Fc receptors on macrophages, resulting in cell death by phagocytosis, i.e. phagoptosis.

Secondary allergic T cell responses are regulated by dendritic cell-derived thrombospondin-1 in the setting of allergic eye disease

Allergic eye disease, as in most forms of atopy, ranges in severity among individuals from immediate hypersensitivity to a severe and debilitating chronic disease. Dendritic cells play a key role in stimulating pathogenic T cells in allergen re-exposure, or secondary responses. However, molecular cues by dendritic cells underpinning allergic T cell response levels and the impact that this control has on consequent severity of allergic disease are poorly understood. Here, we show that a deficiency in thrombospondin-1, a matricellular protein known to affect immune function, has subsequent effects on downstream T cell responses during allergy, as revealed in an established mouse model of allergic eye disease. More specifically, we demonstrate that a thrombospondin-1 deficiency specific to dendritic cells leads to heightened secondary T cell responses and consequent clinical disease. Interestingly, whereas thrombospondin-1-deficient dendritic cells augmented activity of allergen-primed T cells, this increase was not recapitulated with naïve T cells in vitro. The role of dendritic cell-derived thrombospondin-1 in regulating secondary allergic T cell responses was confirmed in vivo, as local transfer of thrombospondin-1-sufficient dendritic cells to the ocular mucosa of thrombospondin-1 null hosts prevented the development of augmented secondary T cell responses and heightened allergic eye disease clinical responses. Finally, we demonstrate that topical instillation of thrombospondin-1-derived peptide reduces T cell activity and clinical progression of allergic eye disease. Taken together, this study reveals an important modulatory role of dendritic cell-derived thrombospondin-1 on secondary allergic T cell responses and suggests the possible dysregulation of dendritic cell-derived thrombospondin-1 expression as a factor in allergic eye disease severity.

Molecular Functions of Glycoconjugates in Autophagy

Glycoconjugates, glycans, carbohydrates, and sugars: these terms encompass a class of biomolecules that are diverse in both form and function ranging from free oligosaccharides, glycoproteins, and proteoglycans, to glycolipids that make up a complex glycan code that impacts normal physiology and disease. Recent data suggest that one mechanism by which glycoconjugates impact physiology is through the regulation of the process of autophagy. Autophagy is a degradative pathway necessary for differentiation, organism development, and the maintenance of cell and tissue homeostasis. In this review, we will highlight what is known about the regulation of autophagy by glycoconjugates focusing on signaling mechanisms from the extracellular surface and the regulatory roles of intracellular glycans. Glycan signaling from the extracellular matrix converges on "master" regulators of autophagy including AMPK and mTORC1, thus impacting their localization, activity, and/or expression. Within the intracellular milieu, gangliosides are constituents of the autophagosome membrane, a subset of proteins composing the autophagic machinery are regulated by glycosylation, and oligosaccharide exposure in the cytosol triggers an autophagic response. The examples discussed provide some mechanistic insights into glycan regulation of autophagy and reveal areas for future investigation.

α-Integrin expression and function modulates presentation of cell surface calreticulin

Calreticulin presentation on the cell surface is an important hallmark of immunogenic cell death (ICD), serving as the prophagocytic signal for macrophages. Cell adhesion is a physiologically relevant stimulus previously shown to increase calreticulin interaction with α-integrins via the juxtamembrane, cytosolic GFFKR motif. This study assessed whether integrin function can regulate surface calreticulin levels in ICD. We generated calreticulin-null T-lymphoblasts and confirmed the loss of surface calreticulin expression on cells treated with doxorubicin, an ICD inducer. Reconstituted expression with full-length calreticulin targeted to the endoplasmic reticulum (ER) successfully rescued doxorubicin-induced surface calreticulin. Reconstitution with a truncation mutant calreticulin targeted to the cytosol led to constitutively high surface calreticulin that was not further elevated by doxorubicin, suggesting calreticulin released from the stressed ER transits the cytosol before its translocation to the cell surface. When stimulated to engage integrin substrates, doxorubicin-treated wild-type T-lymphoblasts exhibited decreased surface calreticulin compared with cells under non-adherent conditions. The inhibitory effect on surface calreticulin was recapitulated for cells in suspension treated with a β1-integrin-activating antibody, 9EG7. Similarly, cells expressing a truncated α-integrin cytosolic tail, bearing only the juxtamembrane GFFKR calreticulin-binding motif, exhibited low surface calreticulin with doxorubicin treatment under non-adherent conditions. Using partial permeabilization techniques to distinguish between cytosolic and ER staining, we found that ICD inducers promoted the accumulation of cytosolic calreticulin with negligible change in total calreticulin, suggesting that integrin-mediated inhibition of surface calreticulin was due to reduced cytosolic to surface translocation. T-lymphoblasts co-treated with an ICD inducer and 9EG7 exhibited reduced phagocytosis by macrophages when compared with treatment with only ICD inducer. This study reveals a previously uncharacterized function of integrins as negative regulators of ICD by suppressing presentation of cell surface calreticulin.

Genome-wide association study and biological pathway analysis of the Eimeria maxima response in broilers

Background

Coccidiosis is the most common and costly disease in the poultry industry and is caused by protozoans of the Eimeria genus. The current control of coccidiosis, based on the use of anticoccidial drugs and vaccination, faces serious obstacles such as drug resistance and the high costs for the development of efficient vaccines, respectively. Therefore, the current control programs must be expanded with complementary approaches such as the use of genetics to improve the host response to Eimeria infections. Recently, we have performed a large-scale challenge study on Cobb500 broilers using E. maxima for which we investigated variability among animals in response to the challenge. As a follow-up to this challenge study, we performed a genome-wide association study (GWAS) to identify genomic regions underlying variability of the measured traits in the response to Eimeria maxima in broilers. Furthermore, we conducted a post-GWAS functional analysis to increase our biological understanding of the underlying response to Eimeria maxima challenge.

Results

In total, we identified 22 single nucleotide polymorphisms (SNPs) with q value <0.1 distributed across five chromosomes. The highly significant SNPs were associated with body weight gain (three SNPs on GGA5, one SNP on GGA1 and one SNP on GGA3), plasma coloration measured as optical density at wavelengths in the range 465–510 nm (10 SNPs and all on GGA10) and the percentage of β2-globulin in blood plasma (15 SNPs on GGA1 and one SNP on GGA2). Biological pathways related to metabolic processes, cell proliferation, and primary innate immune processes were among the most frequent significantly enriched biological pathways. Furthermore, the network-based analysis produced two networks of high confidence, with one centered on large tumor suppressor kinase 1 (LATS1) and 2 (LATS2) and the second involving the myosin heavy chain 6 (MYH6).

Conclusions

We identified several strong candidate genes and genomic regions associated with traits measured in response to Eimeria maxima in broilers. Furthermore, the post-GWAS functional analysis indicates that biological pathways and networks involved in tissue proliferation and repair along with the primary innate immune response may play the most important role during the early stage of Eimeria maxima infection in broilers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-015-0170-0) contains supplementary material, which is available to authorized users.

Original insights on thrombospondin-1-related antireceptor strategies in cancer

Thrombospondin-1 (TSP-1) is a large matricellular glycoprotein known to be overexpressed within tumor stroma in several cancer types. While mainly considered as an endogenous angiogenesis inhibitor, TSP-1 exhibits multifaceted functionalities in a tumor context depending both on TSP-1 concentration as well as differential receptor expression by cancer cells and on tumor-associated stromal cells. Besides, the complex modular structure of TSP-1 along with the wide variety of its soluble ligands and membrane receptors considerably increases the complexity of therapeutically targeting interactions involving TSP-1 ligation of cell-surface receptors. Despite the pleiotropic nature of TSP-1, many different antireceptor strategies have been developed giving promising results in preclinical models. However, transition to clinical trials often led to nuanced outcomes mainly due to frequent severe adverse effects. In this review, we will first expose the intricate and even sometimes opposite effects of TSP-1-related signaling on tumor progression by paying particular attention to modulation of angiogenesis and tumor immunity. Then, we will provide an overview of current developments and prospects by focusing particularly on the cell-surface molecules CD47 and CD36 that function as TSP-1 receptors; including antibody-based approaches, therapeutic gene modulation and the use of peptidomimetics. Finally, we will discuss original approaches specifically targeting TSP-1 domains, as well as innovative combination strategies with a view to producing an overall anticancer response.

CD47 signaling pathways controlling cellular differentiation and responses to stress

CD47 is a widely expressed integral membrane protein that serves as the counter-receptor for the inhibitory phagocyte receptor signal-regulatory protein-α (SIRPα) and as a signaling receptor for the secreted matricellular protein thrombospondin-1. Recent studies employing mice and somatic cells lacking CD47 have revealed important pathophysiological functions of CD47 in cardiovascular homeostasis, immune regulation, resistance of cells and tissues to stress and chronic diseases of aging including cancer. With the emergence of experimental therapeutics targeting CD47, a more thorough understanding of CD47 signal transduction is essential. CD47 lacks a substantial cytoplasmic signaling domain, but several cytoplasmic binding partners have been identified, and lateral interactions of CD47 with other membrane receptors play important roles in mediating signaling resulting from the binding of thrombospondin-1. This review addresses recent advances in identifying the lateral binding partners, signal transduction pathways and downstream transcription networks regulated through CD47 in specific cell lineages. Major pathways regulated by CD47 signaling include calcium homeostasis, cyclic nucleotide signaling, nitric oxide and hydrogen sulfide biosynthesis and signaling and stem cell transcription factors. These pathways and other undefined proximal mediators of CD47 signaling regulate cell death and protective autophagy responses, mitochondrial biogenesis, cell adhesion and motility and stem cell self-renewal. Although thrombospondin-1 is the best characterized agonist of CD47, the potential roles of other members of the thrombospondin family, SIRPα and SIRPγ binding and homotypic CD47 interactions as agonists or antagonists of signaling through CD47 should also be considered.

CD47 does not mediate amyloid-β(1-42) protofibril-stimulated microglial cytokine release

Neuroinflammation triggered by accumulation of amyloid-β protein (Aβ) is a significant component of the Alzheimer's disease (AD) brain. Senile plaques composed of Aβ attract and activate microglia cells resulting in cytokine secretion and a proinflammatory environment. The mechanism by which Aβ activates microglia is complex and involves numerous cellular components. One receptor potentially involved in Aβ recognition and the ensuing microglia proinflammatory response is CD47. Since there is significant interest in soluble aggregated Aβ species, we sought to determine if CD47 plays a key role in microglia cytokine release stimulated by soluble Aβ(1-42) protofibrils. Pretreatment of primary murine microglia with the CD47 antagonist peptide 4N1K significantly and potently inhibited both tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) secretion stimulated by Aβ(1-42) protofibrils. 4N1K displayed toxicity to the microglia but only at concentrations much higher than the observed inhibition. Surprisingly, 4N1K also potently inhibited TNFα secretion triggered by lipopolysaccharide which is not known to signal through CD47. Treatment of the microglia with a neutralizing anti-CD47 antibody failed to block the Aβ protofibril response even though comparable samples were completely inhibited by 4N1K. Finally, Aβ(1-42) protofibrils stimulated similar levels of secreted TNFα production in both wild-type and CD47(-/-) microglia and 4N1K still potently inhibited the Aβ protofibril response even in the CD47(-/-) microglia. The overall findings demonstrated that the microglial proinflammatory response to Aβ(1-42) protofibril is not dependent on CD47 and that 4N1K exhibits CD47-independent inhibitory activity.