CD47 (Cluster of Differentiation 47)

Abstract

CD47, also known as integrin-associated protein, is a constitutively and ubiquitously expressed transmembrane receptor. CD47 is conserved across amniotes including mammals, reptiles, and birds. Expression is increased in many cancers and, in non-malignant cells, by stress and with aging. The up-regulation of CD47 expression is generally epigenetic, whereas gene amplification occurs with low frequency in some cancers. CD47 is a high affinity signaling receptor for the secreted protein thrombospondin-1 (THBS1) and the counter-receptor for signal regulatory protein-α (SIRPA, SIRPα) and SIRPγ (SIRPG). CD47 interaction with SIRPα serves as a marker of self to innate immune cells and thereby protects cancer cells from phagocytic clearance. Consequently, higher CD47 correlates with a poor prognosis in some cancers, and therapeutic blockade can suppress tumor growth by enhancing innate antitumor immunity. CD47 expressed on cytotoxic T cells, dendritic cells, and NK cells mediates inhibitory THBS1 signaling that further limits antitumor immunity. CD47 laterally associates with several integrins and thereby regulates cell adhesion and migration. CD47 has additional lateral binding partners in specific cell types, and ligation of CD47 in some cases modulates their function. THBS1-CD47 signaling in non-malignant cells inhibits nitric oxide/cGMP, calcium, and VEGF signaling, mitochondrial homeostasis, stem cell maintenance, protective autophagy, and DNA damage response, and promotes NADPH oxidase activity. CD47 signaling is a physiological regulator of platelet activation, angiogenesis and blood flow. THBS1/CD47 signaling is frequently dysregulated in chronic diseases.

Identity

Alias (NCBI): IAP, MER6, OA3

HGNC (Hugo): CD47

HGNC Alias symbol: IAP, OA3

HGNC Alias name: antigen identified by monoclonal antibody 1D8, antigenic surface determinant protein OA3, integrin associated protein, Rh-related antigen, leukocyte surface antigen CD47, CD47 glycoprotein

HGNC Previous name MER6

HGNC Previous name CD47 antigen (Rh-related antigen, integrin-associated signal transducer)

LocusID (NCBI) 961

Location 3q13.12 (Figure 1)

Figure 1.

Chromosomal location of human CD47. Position of the gene on chromosome 3 is indicated in red.

Location_base_pair Starts at 108043094 and ends at 108091088 bp from pter

Local_order telomeric to BBX, centromeric to IFT57

DNA/RNA

Description

The CD47 gene is 48,771 bases in size and is composed of 11 exons encoding a 5234 base mRNA (https://www.ncbi.nlm.nih.gov/nuccore/NM_198793.3) and 5 additional alternatively spliced transcripts (Figure 2) (Schnickel et al., 2002). Transcripts CD47–201 and CD47–202 encode isoforms with different C-terminal cytoplasmic tails. Splicing of alternative 3’-UTRs in the transcripts control localization of newly translated CD47 proteins (Berkovits and Mayr 2015; Ma and Mayr 2018). The long UTR recruits HuR (ELAVL1) and SET and directs CD47 to the cell surface via the endoplasmic reticulum and Golgi, whereas the short UTR directs CD47 mRNA translation to intracellular TIS granules.

Figure 2.

Human CD47 transcripts and intron organization. Two of the six identified CD47 gene transcripts (CD47–201 and CD47–202) encode functional CD47 proteins. Coding exons 1–3 encode the extracellular immunoglobulin-like domain, and exons 3–7 encode the transmembrane domain. Alternative splicing produces CD47 isoforms with short and long forms of the C-terminal cytoplasmic tail with the sequences shown. Short and long forms of the 3’-UTR differentially direct subcellular localization of CD47 isoforms. (adapted from http://useast.ensembl.org/Homo_sapiens/Gene/Splice?db=core;g=ENSG00000196776;r=3:108043091-108091862).

Transcription

In the human CD47 gene, the 5’ sequence from −272 to the ATGs contains binding sites for transcription factors including TFAP2A (AP-2), MAZ, CREB1, SP1, and E2F. Its expression is regulated by a α-Pal/NRF-1 region (Chang and Huang, 2004). CD47 expression is increased in many cancers with progression of disease including ovarian carcinoma, T-cell leukemia and lymphoma, and multiple myeloma (Massuger et al., 1991; Campbell et al., 1992; Raetz et al., 2006; Rendtlew Danielsen et al., 2007; Majeti et al., 2009; Willingham et al., 2012; Matlung et al., 2017; Murata et al., 2018; Logtenberg et al., 2020). Increased CD47 expression was linked to poor prognosis in many cancers (Willingham et al., 2012; Logtenberg et al., 2020). However, analysis of TCGA RNAseq data indicated that the inverse correlation between CD47 mRNA expression and survival is not universal. Increased CD47 mRNA expression in melanomas is positively associated with increased survival (Nath et al., 2019).

Increased CD47 transcription in cancer is driven by a variety of factors including MYC (Casey et al., 2016). Hypoxia-inducible factor-1 ( HIF1A) directly induces CD47 expression in breast cancer (Zhang et al., 2015). This may account, in part, for the upregulation of CD47 as cancers are poorly perfused and hypoxic. The CD47 signaling ligand THBS1 was increased in response to hypoxia in a HIF-dependent manner (Labrousse-Arias et al., 2016). Similarly, SRSF10, via mIL1RAP-NF-kB, induced CD47 expression (Liu et al., 2018). CD47 expression in cancer cells was reduced after treatment with BRAF / MAP2K7 (MEK) inhibitors (Liu et al., 2017) and the DNER (BET) inhibitor JQ1 (Li et al., 2019). Expression of mutant isocitrate dehydrogenase 1 in gliomas led to disruption of PKM - CTNNB1 (β-Catenin) - SMARCA4 (BRG1) transcriptional regulation and decreased CD47 expression (Gowda et al., 2018).

Cancer therapy can also alter CD47 expression. Multiple chemotherapeutic drugs including carboplatin, doxorubicin, gemcitabine, and paclitaxel induced CD47 expression (Samanta et al., 2018). MIR222 downregulated CD47 expression in irradiated tumour cells (Shi et al., 2019).

In contrast to cancers, CD47 was downregulated in multiple sclerosis lesions by MIR34A, MIR155 and MIR326, which target the 3’ UTR of CD47 (Junker et al., 2009). MIR34A downregulated CD47 expression via PI3K/AKT and protected cells in the spinal cord from apoptosis (Qi et al., 2019).

Pseudogene

none identified

Protein

Description

Alternative exon splicing produces CD47 isoforms with short or long C-terminal cytoplasmic tails (Figure 3). The CD47 long isoform precursor contains 323 amino acids, has a mass of 35214 Da, and contains an 18 residue N-terminal signal peptide. The mature long isoform protein comprises residues 19–323, and the short isoform comprises residues 19–305. The N-terminal residue of the mature protein Gln-19 is enzymatically modified to pyrrolidone carboxylic acid (pyroGlu) (Logtenberg et al., 2019), which is required for binding to SIRPA. Mature CD47 is an integral membrane protein that contains an extracellular immunoglobulin domain and a transmembrane domain with 5 membrane spanning segments related to the presenilins (Figure 3). The long isoform cytoplasmic tail contains a ubiquitinylation site at Lys-317 (Kim et al., 2011). The protein contains disulfide bonds linking Cys at positions 33 to 263, which links the IgV domain to the transmembrane domain (Figure 3), and 41 to 114 within the IgV domain. Heterogeneous N-linked glycosylation is found at asparagine residues 23, 34, 50, 73, 111, and 206 (Hatherley et al., 2008; Shiromizu et al., 2013) which results in the typical diffuse migration of CD47 at 50–60 kDa on SDS gel electrophoresis. In several cell types, CD47 is further modified to an apparent of molecular mass >250 kDa by heparan and chondroitin sulfate glycosaminoglycan modification at residue Ser-64, which is required for THBS1-dependent inhibition of T cell receptor signaling (Kaur et al., 2011).

Figure 3.

Structure and posttranslational modifications of CD47 protein. The left panel shows the orientation of CD47 in the plasma membrane. The extracellular IgV domain is modified by several asparagine-linked oligosaccharides and by heparan and chondroitin sulfate glycosaminoglycans at Ser-64 and Ser-79 (Kaur et al., 2011). Ser-64 modification is required for THBS1 signaling. Gln-19 is enzymatically modified to a pyroglutamyl residue required for binding to SIRPA, and Lys-317 can be ubiquitinylated. The right panel shows a space filling model of the IgV domain bound to the extracellular region of SIRPA (Hatherley et al., 2008). Direct binding assays demonstrated that THBS1 blocks SIRPA binding to CD47, but the location of the THBS1 binding site on CD47 remains to be determined (Isenberg et al., 2009).

Expression

CD47 is ubiquitously expressed on hematopoietic cells including thymocytes, T and B cells, monocytes, platelets, and erythrocytes, as well as on epithelial, endothelial (Isenberg et al., 2006), vascular smooth muscle (Isenberg et al., 2007) and neural cells, platelets, fibroblasts, sperm, and tumor cell lines (Barclay et al., 1997). CD47 homozygous knockout (Cd47−/−) mice are viable and fertile but exhibit defects in responses to some pathogens (Lindberg et al., 1996; Navarathna et al., 2015; Nath et al., 2018). Due to lack of inhibitory SIRPA signaling, wild type mice eliminated cd47−/− RBCs via erythrophagocytosis, which identified CD47 as a marker of self commonly known as a “don’t eat me” signal (Oldenborg et al., 2000). Under inflammatory conditions or infection, the cd47−/− mice developed anemia and splenomegaly (Bian et al., 2016). Following intestinal epithelium wounding, cd47−/− mice had delayed healing (Reed et al., 2019). In contrast, cd47−/− mice exhibited enhanced protection from ionization radiation (Isenberg et al., 2008), thermal injury (Soto-Pantoja et al., 2014), ischemia, ischemia-reperfusion (Isenberg et al., 2008), hypoxia- (Rogers et al., 2017b) and sickle cell disease-mediated (Novelli et al., 2019) pulmonary hypertension, and Fas-mediated apoptosis (Manna et al., 2005). Null animals showed enhanced vasorelaxation and blood flow via increased nitric oxide/cGMP and VEGF signaling (Isenberg et al., 2007; Kaur et al., 2010; Bauer et al., 2010). Young cd47−/− mice had more efficient and more numerous mitochondria in certain skeletal muscles (Frazier et al., 2011), more stem cells and self-renewal capacity (Kaur et al., 2013), and global protection of anabolic metabolites (Miller et al., 2015). Increased or decreased expression of CD47 was reported in several nonmalignant diseases and is associated with pathogenesis as detailed below.

Increased expression of CD47 in malignant tissues was first reported in ovarian cancer (Massuger et al., 1991; Campbell et al., 1992), and subsequently confirmed in various solid tumors and hematologic malignancies (Matlung et al., 2017; Murata et al., 2018; Logtenberg et al., 2020; Wiersma et al., 2015). RNAseq data from the TCGA PanCancer Atlas indicated that CD47 mRNA expression is highest in human ovarian serous cystadenocarcinoma followed by uterine corpus endometrial carcinoma, lung adenocarcinoma and head and neck squamous cell carcinoma (Figure 5). The high expression of CD47 in ovarian cancers was explored as an imaging modality and strategy for targeted radiotherapy and drug delivery (Massuger et al., 1991; Lu et al., 2001). However, subsequent appreciation of the ubiquitous expression of CD47 in nonmalignant cells limited further development of this approach.

Figure 5.

Locations of identified mutations in CD47 from cancers in the TCGA PanCancer Atlas (analysis of samples from 10,953 individuals). The upper panel represents the frequency of CD47 gene alterations in TCGA Pan-Cancer data (10,953 individuals/10967 samples from 32 studies) classified by cancer type using cBioPortal tools. Green = mutation, purple = fusion, blue = deletion, red = amplification, grey = multiple alterations. The lower panel presents associations of mutation and copy number variation with CD47 mRNA expression. Data is from The Cancer Genome Atlas (TCGA) using cBioPortal tools to analyze data from 10,953 individuals (Cerami et al., 2012; Gao et al., 2013).

Elevated CD47 expression is a prognostic marker in some cancers, with higher CD47 protein and/or mRNA expression associated with decreased survival, which was attributed to SIRPA-dependent suppression of tumor cell phagocytosis by macrophages (Oldenborg et al., 2000; Jaiswal et al., 2009; Willingham et al., 2012). Alternatively, several studies have shown that elevated CD47 expression supports the maintenance of cancer stem/tumor initiating cells, which in turn provides a selective pressure for maintaining elevated CD47 expression (Lee at al., 2014; Kaur et al., 2016; Kaur and Roberts, 2016). However, analysis of TCGA data indicated that elevated CD47 mRNA expression has a protective function in some cancers including cutaneous melanoma (Nath et al., 2019). Elevated CD47 expression in melanoma correlated with markers of enhanced T cell and NK cell-mediated antitumor immunity.

Localisation

CD47 mRNA containing the long 3’ UTR is targeted to the ER where SET binds to the cytoplasmic domain and, with activation of RAC1, translocates CD47 to the plasma membrane (Berkovits and Mayr 2015). CD47 translated from mRNA containing the short UTR is targeted to a membraneless cytoplasmic intracellular compartment containing TIS granules (Ma and Mayr 2018). CD47 function may depend on its localization as expression of CD47 encoded by the short, but not the long, UTR isoform restored radiosensitivity in a CD47-deficient T cell line (Berkovits and Mayr 2015). CD47 is also present on extracellular vesicles isolated from body fluids and regulates the biological cargo and intercellular signaling function of these vesicles (Kaur et al., 2014; Kibria et al., 2016; Tong et al., 2016).

Function

CD47 is also known as integrin associated protein based on its initial isolation by co-purification with beta-3 integrin ( ITGB3) (Lindberg et al., 1993). Ligation of CD47 regulates the activation of associated integrins and their function in mediating cell adhesion and migration (Cooper et al., 1995; Gao et al., 1996; Wang and Frazier 1998; Yoshida et al., 2000; Barazi et al., 2002; Brittain et al., 2004). Although it has only a small cytoplasmic tail, CD47 interacts with the cytoplasmic partners ubiquilin-1 and ubiquilin-2 (UBQLN1 and UBQLN2, formerly known as PLIC1 and PLIC2) (Wu et al., 1999) and BNIP3 (Lamy et al., 2003). Ubiquilins mediate CD47 interaction with heterotrimeric G proteins containing Giα (GNAI1) (N’Diaye et al., 2003; Fujimoto et al., 2003; Frazier et al., 1999). The extracellular domain of CD47 interacts with its counter-receptor signal regulatory protein-α (SIRPA, also known as SIRPα, SHPS-1, BIT, P84), which is expressed on dendritic cells, and macrophages, in synapse-rich regions of the brain, and on numerous other cell types including endothelial cells, vascular smooth muscle cells (Han et al., 2000; Jiang et al., 1999), and renal tubular epithelial cells (Yao et al., 2014). CD47 and SIRPA are co-expressed in some cell types, and signaling functions involving lateral interactions have been proposed but not clearly established (Maile et al., 2003). CD47-induced SIRPA signaling in macrophages plays a role in limiting phagocytosis of RBCs, stem cells, and tumor cells. CD47 laterally associates with VEGFR2 ( KDR) in endothelial cells (Kaur et al., 2010) and Jurkat T cells (Kaur et al., 2014). CD47 also associates with the Rh blood group antigen complex, and deficiency of RHCE, band 4.2 ( EPB42), or RHAG proteins leads to decreased CD47 expression (Van Kim et al., 2006; Flatt et al., 2012; Cambot et al., 2013). THBS1 signaling via CD47 on T cells inhibits their activation and effector functions (Li et al., 2001; Li et al., 2002; Lamy et al., 2007; Kaur et al., 2011; Miller et al, 2013). Conversely, CD47-dependent integrin activation can co-stimulate T cell receptor signaling, and its deficiency leads to T cell anergy (Reinhold et al., 1999).

CD47 binds to the C-terminal domain of THBS1 (Brown and Frazier 2001; Isenberg et al., 2009) and mediates calcium (Schwartz et al., 1993), cAMP (Wang et al., 1999; Manna and Frazier 2003; Manna and Frazier 2002; Yao et al., 2011), and nitric oxide/cGMP signaling (Isenberg et al., 2006; Rogers et al., 2017a), hydrogen sulfide biosynthesis (Kaur et al., 2015; Soto-Pantoja et al., 2015), cell survival from ionization radiation and chemotherapeutic drugs (Kaur et al., 2019; Soto-Pantoja et al., 2015), autophagy (Soto-Pantoja et al., 2012), stem cell self-renewal (Kaur et al., 2013) and extracellular vesicle signaling (Kaur et al., 2018).

CD47 differentially regulates normal and malignant cell responses to genotoxic damage caused by ionizing radiation and chemotherapeutic drugs (Maxhimer et al., 2009; Feliz-Mosquea et al., 2018; Kaur et al., 2019). CD47 null or THBS1 null mice were highly resistant to high-dose radiation with minimal soft-tissue or bone marrow injury (Isenberg et al., 2008). This response was mediated by an increase in protective autophagy (Soto-Pantoja et al., 2012; Feliz-Mosquea et al., 2018), anabolic metabolism, antioxidant, and DNA repair pathways (Miller et al., 2015). However, in cancers, disruption of THBS1-CD47 signaling sensitized tumors in immune-competent mice to ionizing radiation and chemotherapeutic drugs (Maxhimer et al., 2009; Feliz-Mosquea et al., 2018). This effect was mediated by activation of T and NK cell-dependent tumor killing (Soto-Pantoja et al., 2014; Nath et al., 2019). Treatment with an oligonucleotide morpholino that blocks CD47 mRNA translation, resulting in decreased total CD47 protein, protected wild type mice from lethal whole-body radiation (Soto-Pantoja et al., 2013).

Similarly, CD47 plays divergent roles in regulation of stem cell self-renewal. Lack of CD47 in healthy tissues and cells upregulates the essential self-renewal transcription factors POU5F1 (Oct3/4), SOX2, KLF4, and MYC and increases the abundance of stem cells (Kaur et al., 2013). Conversely, in breast cancer, glioma, and hepatocellular carcinomas stem/tumor initiating cells, inhibiting CD47 signaling decreased cancer stem cell self-renewal and asymmetric cell division (Lee et al., 2014; Lo et al., 2016; Kaur et al., 2016; Kaur and Roberts 2016; Li et al., 2017a).

Homology

CD47 is a member of the immunoglobin super family that is conserved across amniotes including mammals, reptiles, and birds (https://www.ncbi.nlm.nih.gov/gene/961/ortholog/?scope=32524). The IgV domain of CD47 is distantly related to the Drosophila melanogaster wrapper (AF134113, Stork et al. 2009), a GPI-linked membrane protein involved in axon ensheathment by glia (Noordermeer et al., 1998). The transmembrane domain shares homology with the presenilins (Roberts et al., 2012). A viral ortholog of CD47 was first reported in myxoma virus (AF170726) (Cameron et al., 1999) and contributed to virulence by limiting macrophage activation during infection in rabbits (Cameron et al., 2005). CD47-related genes are present in many Poxviridae including Vaccinia virus CD47 (AAB96477), variola virus CD47 (P33853) and Yaba monkey tumor virus (AB025319). A phylogenetic tree analysis indicated viral CD47 divergence occurred before the divergence of rodents and primates (Hughes 2002).

Mutations

CD47 coding variations in humans were identified in the ExAC database (Lek et al., 2016) (Figure 4). CD47 mRNA expression and somatic gene alterations have been identified in some cancers (Figure 5). Human cancer CD47 mutations included 41 missense (green), 2 truncating (black), 3 splice, and 4 fusion aberrations (TEAD1-CD47 in a bladder urothelial carcinoma, and RNF183-CD47, RASGRP1-CD47, SPON1-CD47 in uterine endometrial carcinomas).

Figure 4.

The distribution of observed synonymous, missense and loss of function (LoF) mutations in the exons of CD47 is presented in the upper panel. The lower panel presents the expected and observed numbers of each variant type. The lower than expected number of LoF mutations indicates an 89% probability that the CD47 gene is loss-intolerant (pLI).

Epigenetics

CD47 was upregulated in human astrocytoma cell lines. Blocking CD47 in these cells led to decreased expression of UHRF1 (Ubiquitin-like containing PHD and RING finger-1) and increased expression of the tumour suppressor gene CDKN2A (p16 or INK4A) (Boukhari et al., 2015). In multiple myeloma, CD47 expression was upregulated by treating cells with a DNA methyltransferase inhibitor and a histone deacetylase inhibitor (De Beck et al., 2018). HDAC inhibitor treatment decreased CD47+ leukemic cells and reversed their chemo-resistant phenotype (Yan et al., 2019). CD47 expression in lymphoma cells decreased following treatment with JQ1 (Li et al., 2019). miR-133a inhibited CD47 mRNA and protein expression in laryngeal carcinoma cells (Li et al., 2016). Conversely, in a prostate cancer cell line, CD47 epigenetically regulated the expression of Schlafen-11 ( SLFN11), which modifies of cancer cell sensitivity to DNA damaging agents (Kaur et al., 2019).

Germinal

Human CD47 polymorphisms

Polymorphisms in CD47 were linked to cancer risk and outcome for individuals with colorectal cancer (Thean et al, 2018; Lacorz et al., 2013). Fourteen instances of altered CD47 copy number with pathogenic significance were reported to date in ClinVar (https://www.ncbi.nlm.nih.gov/clinvar). In each case, multiple adjacent genes were duplicated or deleted. Thus, specific pathogenic roles for CD47 in these situations remain to be identified. The only CD47 SNP reported in the NCBI occurs in an intron (rs12695175 A/C). This SNP was related to variation in expression of CD47 and associated with immune-mediated skin cell injury in individuals with Pemphigus foliaceus (Bumiller-Bini et al., 2019). Consistent with the lack of nonsense mutations in the NCBI data, exon sequencing of over 60,000 human genomes identified only 1 putative loss-of-function mutation in CD47 versus 11.2 loss-of-function mutations predicted for a gene of its size (Lek et al., 2016) (Figure 4). Based on this, CD47 has an 89% probability of being loss intolerant. Mice lacking CD47 are viable, indicating the gene is not essential in a controlled laboratory setting. However, the impaired immune responses of cd47−/− mice to some pathogens and dysregulation of vascular physiology and hemostasis are potential reasons for the gene to be loss-intolerant in humans (Lindberg et al., 1996; Navarathna et al., 2015; Nath et al., 2018; Soto-Pantoja et al. 2015).

Non-Human CD47 Polymorphisms

The Tibetan plateau is characterized by reduced atmospheric oxygen and increased radiation exposure. High throughput sequencing of blood samples from Tibetan plateau chickens, which reside at approximately 3,650 meters above sea level, found significant enrichment in a missense SNP of CD47 in comparison to blood samples from lowland chickens (Zhang et al., 2016). This is potentially relevant given that CD47 limits cardiovascular response to hypoxia, ischemia, ischemia reperfusion, metabolism and radiation-mediated genotoxic injury. Also, absence of CD47 leads to less oxygen utilization and improved mitochondrial function in mice (Frazier et al., 2011). It is possible the identified CD47 SNP encodes for a mutant protein with less activity and signaling to potentiate adaptation to the low oxygen/high radiation conditions of life at elevated altitude.

Somatic

The incidence of somatic mutations of CD47 in human cancers is low, with a frequency of about 1.7% (The Cancer Genome Atlas, cbioprortal.org). Amplification is the most common variant (Figure 5). CD47 is sporadically amplified in lung squamous, ovarian, and cervical cancers, but rarely in other cancer types. CD47 amplification is associated with increased CD47 mRNA expression (Figure 4, lower panel). The majority of the 50 point mutations identified to date are missense or nonsense. These mutations are randomly distributed and have not revealed any cancer-specific mutation hotspots (Figure 6). Rare mutations that lead to shallow and deep deletion of CD47 are found in uterine endometrial carcinoma, sarcoma, prostate adenocarcinoma, lung squamous cell carcinoma, low grade glioma and colorectal adenocarcinoma (TCGA, PanCancer Atlas).

Figure 6.

Distribution of mutations in CD47 identified in human cancers sequenced in The Cancer Genome Atlas.

Implicated in:

Note

High expression of CD47 was associated with poor prognosis and survival for many types of solid tumors including ovarian carcinoma, glioma, and glioblastoma (Willingham et al, 2012). Further studies established that high CD47 expression is associated with poor prognosis and increased metastasis in colon (Martins, 2020), breast (Baccelli et al., 2014), prostate (Rivera et al., 2015), oral squamous cell carcinoma (Pai et al., 2019), gastric cancer (Yoshida et al., 2015), non-small cell lung carcinoma (Barrera et al., 2017; Arrieta et al., 2020), uveal melanoma (Petralia et al., 2019), and pancreatic carcinoma (Pan et al., 2019). CD47 expression was increased alone, or in combination with other tumor markers including PD-L1 ( CD274) (Papadaki et al., 2020), CD68 (Yuan et al., 2019), CD133 ( PROM1) and CXCR4, in endometrial cancer (Sun et al., 2017), CD44 in colorectal cancer (Fujiwara-Tani et al., 2019), CD133 in (Wang et al., 2019b), and β4 (ITGB4) and CD44v6 in non-invasive (Wang et al., 2018).

CD47 was increased in a stem cell subset isolated from renal tumors (Li et al., 2020) and in diffuse large B cell lymphoma (Kazama et al., 2020; Lin et al., 2020). Increased CD47 expression was characteristic of cancers with more basal/stem phenotypes (Pai et al., 2019).

Colorectal cancer

Prognosis

A common copy number variation at chromosome 3q13.12 encompassing CD47 was significantly associated with risk for developing colorectal cancer in a genome-wide association study of 1000 Singapore Chinese patients with sporadic colorectal cancers and 1000 ethnically, age, and gender matched healthy controls (OR=1.54 (95% CI 1.33 to 1.77, p = 2.9×10–9) (Thean et al., 2018). In a second study of 613 German colorectal cancer patients, the intronic SNP rs12695175 in CD47 was associated with colorectal cancer-specific survival (HR = 2.18, 95 % CI 1.10–4.33, CC versus AA) and with overall survival (HR = 1.99, 95 % CI 1.04–3.81, CC versus AA) (Lacorz et al., 2013). Two polymorphisms in the 3’-UTR of CD47 were associated with distant metastasis. rs9879947 and rs3206652 in the 3’-UTR of CD47 had OR = 1.64, 95 % CI 1.01–2.64 and OR = 1.88, 95 % CI 1.27–2.80, respectively, and the intronic eSNP rs3804639 had an OR = 1.73, 95 % CI 1.17–2.57. The intronic polymorphisms was linked to CD47 expression in lymphoblastoid cell lines (Dixon et al., 2007).

Oncogenesis

No causal relationship between these CD47 copy number variations or polymorphisms and colorectal cancer risk or outcome has been established.

Ovarian carcinoma

Disease

Ovarian antigen-3 (OA3) is an ovarian cancer marker that was subsequently identified as CD47 (Massuger et al., 1991; Campbell et al., 1992). CD47 antibodies showed some utility for imaging of ovarian cancers in patients, and a bispecific antibody recognizing CD3 and CD47 delayed tumor growth in an ovarian carcinoma xenograft model (van Ravenswaay Claasen et al, 1994). Among solid tumors, ovarian cancers showed the strongest association between CD47 expression and overall survival (Willingham et al., 2012). Ovarian cancers had high expression of CD47 and the Lewis Y antigen as compared to benign tissues (Tan et al., 2015).

Prognosis

Elevated CD47 is associated with poor prognosis and metastasis in ovarian cancer (Tan et al., 2015; Brightwell et al., 2016; Li et al., 2017). A bispecific antibody targeting CD47 and mesothelin, which is highly expressed on ovarian carcinoma, enhanced phagocytosis of tumor cells, and inhibited human xenograft tumor growth in mice (Hatterer et al., 2020). Silencing of CD47 in ovarian cancer cells suppressed cell growth and motility (Wang et al., 2019). This may involve suppression of cancer stem cells since aldehyde dehydrogenase-1 ( ALDH1A1)-high ovarian cancer cells expressed elevated CD47 (Sharrow et al., 2016). These data suggest that therapeutic targeting of CD47 could have efficacy against ovarian cancer by mechanisms independent of enhancing innate immunity. Partial remission was reported in a Phase 1 clinical trial in two individuals with ovarian cancer treated with a humanized CD47 antibody (Sikic et al., 2019).

Invasive breast cancers

Prognosis

Analysis of CD47 mRNA expression in bone marrow and peripheral blood identified elevated CD47 as a negative prognostic indicator for disease-free and overall survival in 738 cases of breast cancer (Nagahara et al., 2010). Analysis of molecular subtypes showed the highest CD47 mRNA in basal breast carcinomas, followed by Her2/Neu positive tumors, whereas luminal A and luminal B cancers did not differ significantly from normal (Zhao et al., 2011). Elevated CD47 mRNA in hormone receptor-positive breast carcinoma was associated with lymph node metastasis, and co-expression withMET adversely affected overall survival (Baccelli et al., 2014). Circulating breast tumor cell numbers expressing EPCAM, CD44, CD47, and MET, but not EPCAM+ circulating tumor cells, negatively correlated with overall survival and increased metastasis (Baccelli et al., 2013). High CD47 and/or PD-L1 protein expression on circulating tumor cells correlated with disease progression, shorter progression-free survival, relapse, and death (Papadaki et al., 2020). Invasive breast carcinomas in TCGA with greater than mean CD47 mRNA had decreased overall survival (Kaur et al., 2016). However, the survival advantage of cancers with CD47SNAI1 and ZEB1 (Noman et al., 2018). Metformin treatment suppressed breast cancer stem cells via MIR708 -mediated suppression of CD47 expression, suggesting a therapeutic approach to overcome chemoresistance (Tan et al., 2019). Treatment with a CD47 blocking antibody suppressed breast cancer stem cells by suppressing KLF4 expression and EGFR expression and signaling (Kaur et al., 2016).

Oncogenesis

Based on informatics analysis, CD47 was identified as a hub gene involved in estrogen-induced breast carcinogenesis (Bhar et al., 2013). HIF-1α-dependent induction of CD47 expression was implicated in the maintenance of breast cancer stem cells and prevented their phagocytic clearance (Zhang et al., 2015). CD47 expression in breast carcinoma cells is also regulated by HSPA5 (glucose regulated protein 78, GRP78) (Cook et al., 2016). THBS1/CD47 signaling was implicated in the escape of triple negative breast cancer cells from senescence following chemotherapy (Guillon et al., 2019).

Haematological malignancies

Note

Elevated CD47 expression in haematological malignancies

Prognosis

CD47 was upregulated on circulating hematopoietic stem cells and acute myeloid leukemia cells and associated with increased tumorigenicity in mice (Jaiswal et al., 2009). High CD47 expression on acute myeloid leukemic cells was associated with worse overall survival (Majeti et al., 2009). A similar correlation between high CD47 expression and decreased overall survival was reported in acute lymphoblastic leukemia (Chao et al., 2011; Galli et al., 2015) and adult T-cell leukemia (Yanagita et al., 2020).

Oncogenesis

High CD47 expression promoted survival of malignant cells in the circulation by protecting the cells from phagocytic clearance by macrophages (Majeti et al., 2009). CD47 opposes upregulation of phagocytosis mediated by calreticulin displayed on malignant cells (Chao et al., 2010). Conversely, CD47 activation directly induced death of chronic lymphocytic leukemia cells (Mateo et al., 1999). CD47-mediated cell death was reported inmultiple myeloma (Kikuchi et al., 2005,), promyelocytic leukemia (Saurnet 2005), T-cell acute lymphoblastic leukemia (Uscanga-Palomeque et al., 2019), acute lymphoblastic leukemia, and B-cell chronic lymphocytic leukemia (Uno et al., 2007; Martinez-Torres et al., 2015). CD47 antibodies and other antagonists of SIRPA binding are intended to activate phagocytosis by macrophages but may also induce direct CD47-mediated cancer cell death.

Cutaneous melanoma

Prognosis

In contrast to most published correlations between CD47 expression and negative prognosis in solid tumors, increased CD47 expression in human melanomas positively correlated with improved overall and progression-free survival (Nath et al., 2019). Elevated CD47 correlated with molecular markers of NK and cytotoxic T cell infiltration in the tumors, suggesting that increased immune surveillance may be responsible for the improved survival of melanoma patients with elevated CD47 mRNA. CD47 mRNA expression in melanomas was positively correlated with expression of the T-cell inhibitory receptor CTLA4 and its counter receptors CD80 and CD86 (Schwartz et al., 2019). Combining CD47 and CTLA4 blockade improved killing of human melanoma cells by cytotoxic T cells and, in combination with tumor irradiation, improved survival of mice bearing syngeneic melanomas.

Oncogenesis

Increased or decreased CD47 expression was reported in several nonmalignant diseases and is associated with pathogenesis.

Pemphigus foliaceus (PF)

Note

CD47 rs12695175*G (OR = 1.77, p = 0.0043)

Disease

PF is an autoimmune disease that results in increased loss of keratinocytes, blistering and skin fragility. Variation in CD47 expression and CD47 SNPs associated with immune-mediated skin cell killing (Bumiller-Bini et al., 2019). CD47 and SIRPA expression are positively associated with immunogenic cell death pathways (Matlung et al., 2017). This is interesting given the autoimmune nature of this disease and suggest that the SNP may alter CD47 function as an immune cell checkpoint signal. Further suggesting a link between degraded CD47 signaling in these individuals and increased autoimmunity is the finding of increased autoimmune-mediated type 1 diabetes in individuals with Pemphigus foliaceus (Parameswaran et al., 2015).

Rh deficiency syndrome

Note

Rhnull patients and reduction of RhCc/Ee antigens (CD47)

Disease

Rh deficiency syndromes are due to polymorphisms in genes encoding components of the Rh protein complex. Several of the Rh deficiency syndromes are associated with a decrease or absence of CD47 on red blood cells {Cartron, 1994; Cherif-Zahar et al., 1996). Two mutations in RHAG led to loss of CD47 on red cells (Polin et al., 2016). A homozygous Coimbra patient that lacked band 3 expression on RBCs also lost CD47 expression, which was restored when band 3 was reexpressed (Satchwell et al., 2014 PMID 25344524). Biallelic mutations in RHCE resulted in the D (- -) red blood cell phenotype and were associated with reduced CD47 (Flatt et al., 2012). CD47 was expressed at normal levels on cells other than erythrocytes from Rh null individuals. This suggests that CD47 protein synthesis is not impaired in some cells from Rh null individuals. Rather, the reduction in RBC CD47 may be due to a defect in transport of Rh complex proteins to assemble CD47 at the cell surface (Cherif Zahar et al., 1996).

Genetic disorders affecting the red blood cell (RBC) cytoskeleton.

Disease

Genetic mutations affecting elements of the RBC cytoskeleton can decrease CD47 expression. Hereditary spherocytosis (HS) is a hemolytic anemia caused by mutations in the red cell cytoskeletal spectrins ( SPTA1 and SPTB), ankyrin ( ANK1), band 4.2 (EPB42) or band 3 ( SLC4A1) and is characterized by decreased CD47 expression (Bruce et al., 2002; Bruce et al., 2003; King et al., 2004). Two groups of hereditary spherocytosis patients with band 4.2 mutations had 80–90% less CD47 (Bruce et al., 2002; Mouro-Chanteloup et al., 2003). Despite the deficiency in CD47 on the cell surface, increased RBC phagocytosis was not observed (Arndt and Garratty 2004). RBCs from individuals with the HS variant hereditary pyropoikilocytosis showed a further decrease in CD47 on RBCs (King et al., 2011).

Coronary artery and vascular disease

Note

CD47 expression in human vascular endothelial cells and systemic arteries and veins associated with vasculopathy

Prognosis

CD47 was expressed on human endothelial progenitor cells and limited angiogenic activity (Smadja et al., 2011). Human saphenous vein progenitor (SVP) cells expressed significantly more CD47 than CD36, while blocking CD47 limited THBS1-stimulated SVP cell migration. This may be relevant as SV progenitors play a role in saphenous vein graft remodelling after coronary bypass surgery (Garoffolo et al., 2020). CD47 expression was upregulated in the mural compartment of distal human pulmonary arteries from individuals with end-stage pulmonary hypertension compared to arteries from individuals without lung or cardiovascular disease (Rogers et al., 2017). CD47 mRNA and protein were increased in systemic arteries from otherwise healthy old as compared to young individuals and this was associated with decreased angiogenic capacity (Ghimire et al., 2020). Interestingly, treatment of arteries from aged individuals with a CD47 antibody improved their angiogenic capacity. CD47 protein and mRNA expression were increased in carotid and coronary arteries from individuals with atherosclerosis compared to vessels from healthy individuals. In diseased vessels, CD47 was especially localized to the necrotic core of atherosclerotic lesions (Kojima et al., 2016). However, it is not clear if this represented an artifact, as RBCs highly express CD47 and extravasate into atherosclerotic lesions.

Myocardial infarction and heart failure

Prognosis

CD47 expression was increased and localized to infarcted myocardium and cardiomyocytes in hearts from individuals who died of acute myocardial infarction (Zhang et al., 2017). CD47 protein, but not mRNA, expression was decreased in left ventricle (LV) samples from individuals with end-stage LV heart failure compared to samples from healthy controls (Sharifi-Sanjani et al., 2014). This variation in expression may be secondary to several factors including were tissue samples were obtained from, as related to the site of injury, to the degree of injury between donors and specifics of each disease process.

Exercise physiology / Inactivity and lack of exercise

Prognosis

Hypoxic exercise resulted in decreased RBC CD47 expression in sedentary men compared to expression in RBCs from normoxic exercised men. The loss of RBC CD47 was associated with decreased total actin and spectrin and reduced RBC deformability (Mao et al., 1985). In rodents, exercise decreased tissue THBS1 (Pourheydar et al., 2020). Related to this, both CD47 and THBS1 were increased in sickle cell disease (Brittain et al., 2001), a process itself characterized by decreased RBC deformability and loss of tissue prefusion.

Neurodegenerative disease

Disease

CD47 expression in chronic neurodegenerative disease

Prognosis

Human brain microvascular endothelial cells (HBMEs) and smooth muscle cells expressed CD47. A THBS1-derived peptide, that putatively targets CD47, increased VEGFA production by HBMEs (Xing et al., 2010). This is consistent with the inhibitory role THBS1-CD47 has on VEGF signaling. CD47 mRNA and protein were decreased in brain lesions from individuals with multiple sclerosis versus samples from people without disease (Han et al., 2012). CD47 protein expression was increased in certain cerebral vessels in tissue samples from Alzheimer’s disease patients carrying the ApoE3/4 allele. (Lee G., 2018). This is possibly relevant given that amyloid peptides regulate CD47 signaling by interacting with CD36 (Miller et al., 2010) while THBS1-CD47 signaling increases reactive oxygen species production (Csanyi et al., 2012) and limits anti-inflammatory nitric oxide signaling (Isenberg et al., 2006). Further, CD47-SIRPA signaling protects neurons and myelin from phagocytosis (Gitik et al., 2011; Lehrman et al., 2018).

Lung disease

Note

CD47 expression was increased and associated with several forms of lung disease and with age

Prognosis

CD47 expression was increased in lungs from older versus younger otherwise healthy individuals (Meijles et al., 2017). Plasma CD47 was elevated in individuals with acute exacerbation of chronic obstructive pulmonary disease and correlated with elevated P-selectin (SELP) (Pan et al., 2010). Fibroblasts from lung samples from individuals with pulmonary fibrosis showed increased CD47 expression compared to cells from individuals without lung disease (Cui et al., 2020). This may be important as in some wounds CD47 inhibits fibrosis by limiting TGFB1 (TGF-β) activation (Soto-Pantoja et al., 2014). CD47 is expressed in lung samples from individuals with idiopathic pulmonary fibrosis. Here too, CD47 was up-regulated on fibroblasts from these individuals (Wernig et al., 2017).

Diabetes and metabolic syndrome

Note

CD47 is expressed in circulating cells from individuals with diabetes

Prognosis

CD47 expression was lower in RBCs, and associated with increased ANXA5 (annexin V) expression, from men with metabolic syndrome versus healthy individuals (Straface et al., 2011). This could suggest increased aging in the RBCs from men with metabolic syndrome. Human CD34+ progenitor cells from healthy and Type 2 Diabetics expressed CD47 and treatment with a THBS1-derived peptide, that interacts with CD47, increased cell adhesion (Cointe et al., 2017). This is of interest, as the THBS1 promoter is activated by elevated glucose (Wang et al., 2002).

Obesity

Prognosis

In people, a composite body shape that favoured adiposity/obesity strongly associated with a SNP (rs7640424) for a locus located in an enhancer region 10 kb upstream of CD47 (Ried et al., 2016). This could be important given data in animals that suggest CD47 promotes multiple features of metabolic syndrome (Ghimire et al., 2020). RBC CD47 expression was significantly lower in obese individuals than in non-obese controls and correlated with body mass index (Wiewiora et al., 2017).

Gastrointestinal disease

Note

Decreased CD47 expression was associated with increased immune activation in inflammatory bowel diseases

Prognosis

Human intestinal epithelial cells expressed CD47 which was increased on interaction with collagen type I (Broom et al., 2009). Human CD4+ effectors cells from individuals with Chron’s disease had decreased CD47 expression in inflamed lymph nodes and mucosal tissues (Van et al., 2012). The loss of CD47 in this situation may alter the resolution of inflammation. CD47 expression decreased on naïve human CD4+ T cells on exposure to CD3 and CD28 antibodies (Van et al., 2012).

Renal disease

Note

Loss of CD47 associates with renal disease

Prognosis

CD47 expression was decreased on mesangial cells in membrano-proliferative glomerulonephritis (Hafdi et al., 2000). RBC CD47 expression was decreased in individuals with chronic renal failure that responded to human erythropoietin compared to individuals that did not respond (Georgatzakou et al., 2017).

Hepatitis

Prognosis

Livers from Hispanic individuals with hepatitis C showed increased expression of CD47 (Hevezi et al., 2011).

Blood diseases

Disease

Sickle cell disease, hemolytic anemia, Gaucher’s

Prognosis

CD47 protein was increased in lungs of individuals with Sickle Cell Disease and pulmonary hypertension compared to lungs from individuals without disease (Novelli et al., 2019). RBC CD47 expression was the same on cells from healthy blood donors and cells from patients with auto-immune haemolytic anaemia or immune thrombocytopenia (Ahrens et al., 2006) suggesting that in these individuals low RBC CD47, as putative simulator of RBC phagocytosis, was not the direct cause of the anemia. High-glycerol cryopreservation of human RBCs did not alter CD47 expression (Holovati et al., 2008). Erythrocytes with dysmorphic morphology in Gaucher’s disease had reduced expression of CD47 (Bratosin et al., 2011).

Immune dysfunction

Disease

Burn-related loss of immune capacity associated with increased CD47 expression

Prognosis

Anergic T cells from burn and trauma patients showed increased CD47 expression compared to T cells from healthy individuals. Parenthetically, SHP-1, a downstream effector of SIRPA, was also increased in the anergic T cells (Bandyopadhyay et al., 2007). Burn patients with immune suppressed dendritic cells showed increased CD47-dependent phosphorylation of SHP-1 (PTPN6), and this was associated with greater risk of infection (Bandyopadhyay et al., 2014).

Musculoskeletal disease

Note

Osteoarthritis was associated with less chondrocyte CD47 expression

Prognosis

Chondrocytes from individuals with osteoarthritis had decreased CD47 concurrent with decreased aldehyde dehydrogenase (ALDH) expression (Unguryte et al., 2016). This is likely relevant as ALDH is a stem cell marker and CD47 limits cell pluripotency (Kaur et al., 2013).

Rheumatologic disease

Note

Rheumatoid arthritis synovial cells showed decreased CD47 expression

Prognosis

Synovial mesenchymal stem cells from individuals with rheumatoid arthritis had less CD47 expression compared to similar cells from people with osteoarthritis (Denkovskij et al., 2015). RBC CD47 expression was decreased in individuals with scleroderma (Giovannetti et al., 2012). This is interesting as circulating and tissue expression of the CD47 ligand THBS1 is increased in individuals with scleroderma. T cells and monocytes from patients with rheumatoid arthritis did not show changes in CD47 on exposure to a TNF-α blocker (Eriksson et al., 2010). CD47 was up-regulated in blood cells from individuals with rheumatoid arthritis compared with healthy individuals (Hao et al., 2017).

Eye and ear diseases

Note

CD47 expression correlated with the extent of proliferative retinopathy

Prognosis

Fibrovascular epiretinal membrane cells from individuals with proliferative diabetic retinopathy expressed CD47 (Vereb et al., 2013). Vascular endothelial cells and myofibroblasts from epiretinal membranes of people with proliferative diabetic retinopathy expressed CD47 and this correlated with disease activity (El-Asrar et al., 2013). Photoreceptors from human eyes expressed CD47 (Liu et al., 2020). This is significant given that retinal photoreceptors are dependent upon the second messenger molecules cGMP and cAMP, while THBS1-CD47 signaling negatively regulates both cyclic nucleotides (Yao et al., 2011). Neuroretina samples removed from individual with retinal detachment expressed CD47 but did not express nestin or OCT3/4 (Josifovska et al., 2019). This is consistent with the known role CD47 has in limiting expression of key self-renewal transcription factors including nestin and OCT3/4 (Kaur et al., 2013).

Dental and craniofacial disease

Note

CD47 was increased in immune cells from individuals with periodontitis

Prognosis

Circulating lymphocyte CD47 was increased in individuals with dyslipidaemia and periodontitis compared to cells from healthy individuals (Corbi et al., 2020).