Ecrg4 contributes to the anti-glioma immunosurveillance through type-I interferon signaling

A potential role of human esophageal cancer-related gene-4 in cardiovascular homeostasis

Human esophageal cancer related gene-4 (ECRG-4) encodes a 148-aminoacid pre-pro-peptide that can be processed tissue-dependently into multiple small peptides possessing multiple functions distinct from, similar to, or opposite to the tumor suppressor function of the full-length Ecrg4. Ecrg-4 is covalently bound to the cell surface through its signal peptide, colocalized with the innate immunity complex (TLR4-CD14-MD2), and functions as a 'sentinel' molecule in the maintenance of epithelium and leukocyte homeostasis, meaning that the presence of Ecrg-4 on the cell surface signals the maintained homeostasis, whereas the loss of Ecrg-4 due to tissue injury activates pro-inflammatory and tissue proliferative responses, and the level of Ecrg-4 gradually returns to its pre-injury level upon wound healing. Interestingly, Ecrg-4 is also highly expressed in the heart and its conduction system, endothelial cells, and vascular smooth muscle cells. Accumulating evidence has shown that Ecrg-4 is involved in cardiac rate/rhythm control, the development of atrial fibrillation, doxorubicin-induced cardiotoxicity, the ischemic response of the heart and hypoxic response in the carotid body, the pathogenesis of atherosclerosis, and likely the endemic incidence of idiopathic dilated cardiomyopathy. These preliminary discoveries suggest that Ecrg-4 may function as a 'sentinel' molecule in cardiovascular system as well. Here, we briefly review the basic characteristics of ECRG-4 as a tumor suppressor gene and its regulatory functions on inflammation and apoptosis; summarize the discoveries about its distribution in cardiovascular system and involvement in the development of CVDs, and discuss its potential as a novel therapeutic target for the maintenance of cardiovascular system homeostasis.

Cardiac Expression of Esophageal Cancer-Related Gene-4 is Regulated by Sp1 and is a Potential Early Target of Doxorubicin-Induced Cardiotoxicity

Esophageal Cancer-Related Gene 4 (Ecrg4) expressed in cardiomyocytes and the cardiac conduction system is downregulated during cardiac ischemia and atrial fibrillation. To explore whether Ecrg4 plays any role in doxorubicin (DOX)-induced cardiotoxicity. Rats and neonatal rat cardiomyocytes (NRCMs) were employed to study the effect of DOX on Ecrg4 transcription. Bioinformatics combined with promoter analysis were used to map the rat Ecrg4 promoter. ChIP assay was used to evaluate the binding of Sp1 to the Ecrg4 promoter. Transient transfection was used to study the effect of Sp1 on the expression of endogenous Ecrg4. DOX decreased endogenous Ecrg4 gene expression in the heart and cultured NRCMs. In silico analysis showed that the 5'UTR immediately upstream of the start codon ATG, harbors a putative promoter that is GC-rich, and contains CpG islands, multiple overlapping Sp1sites. Transcription is initiated mainly on the 'C' at - 15. Serial 5'-deletion combined with dual-luciferase assays showed that the rat Ecrg4 core promoter resides at - 1/- 800. Sp1 transactivated Ecrg4 gene, which was almost abolished by DOX. Furthermore, ChIP assay showed that Sp1 specifically bound to the Ecrg4 promoter was interrupted by DOX. Finally, DOX suppressed Sp1 protein expression, and restoration of Sp1 increased Ecrg4 expression that was resistant to DOX-induced Ecrg4 downregulation. Importantly, cardiomyocyte-specific loss of Ecrg4 significantly enriched the differentially expressed proteins in the signaling pathways commonly involved in DOX-induced cardiotoxicity. Our results indicate that Sp1 mediates DOX-induced suppression of Ecrg4, which may contribute indirectly to its cardiotoxicity.

Reprogramming the immunosuppressive microenvironment of IDH1 wild-type glioblastoma by blocking Wnt signaling between microglia and cancer cells

The vast majority (>90%) of glioblastoma (GBM) patients belong to the isocitrate dehydrogenase 1 wild type (IDH1^WT) group which exhibits a poor prognosis with a median survival of less than 15 months. This study demonstrated numerous immunosuppressive genes as well as β-catenin gene, pivotal for Wnt/β-catenin signaling, were upregulated in 206 IDH1^WT glioma patients using the Chinese Glioma Genome Atlas (CGGA) database. The increase in microglia with an immunosuppressive phenotype and the overexpression of β-catenin protein were further verified in IDH1^WT GBM patients and IDH1^WT GL261 glioma allografts. Subsequently, we found that IDH1^WT GL261 cell-derived conditioned medium activated Wnt/β-catenin signaling in primary microglia and triggered their transition to an immunosuppressive phenotype. Blocking Wnt/β-catenin signaling not only attenuated microglial polarization to the immunosuppressive subtype but also reactivated immune responses in IDH1^WT GBM allografts by simultaneously enhancing cytotoxic CD8⁺ T cell infiltration and downregulating regulatory T cells. Positron emission tomography imaging demonstrated enhanced proinflammatory activities in IDH1^WT GBM allografts after the blockade of Wnt signaling. Finally, gavage administration of a Wnt signaling inhibitor significantly restrained tumor proliferation and improved the survival of model mice bearing IDH1^WT GBM allografts. Depletion of CD8⁺ T cells remarkably abrogated the therapeutic efficacy induced by the Wnt signaling inhibitor. Overall, the present work indicates that the crosstalk between IDH1^WT glioma cells and immunosuppressive microglia is important in maintaining the immunosuppressive glioma microenvironment. Blocking Wnt/β-catenin signaling is a promising complement for IDH1^WT GBM treatment by improving the hostile immunosuppressive microenvironment.

Microglial Homeostasis Requires Balanced CSF-1/CSF-2 Receptor Signaling

CSF-1R haploinsufficiency causes adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP). Previous studies in the Csf1r^+/- mouse model of ALSP hypothesized a central role of elevated cerebral Csf2 expression. Here, we show that monoallelic deletion of Csf2 rescues most behavioral deficits and histopathological changes in Csf1r^+/- mice by preventing microgliosis and eliminating most microglial transcriptomic alterations, including those indicative of oxidative stress and demyelination. We also show elevation of Csf2 transcripts and of several CSF-2 downstream targets in the brains of ALSP patients, demonstrating that the mechanisms identified in the mouse model are functional in humans. Our data provide insights into the mechanisms underlying ALSP. Because increased CSF2 levels and decreased microglial Csf1r expression have also been reported in Alzheimer's disease and multiple sclerosis, we suggest that the unbalanced CSF-1R/CSF-2 signaling we describe in the present study may contribute to the pathogenesis of other neurodegenerative conditions.

Glioblastoma-initiating cell heterogeneity generated by the cell-of-origin, genetic/epigenetic mutation and microenvironment

Glioblastoma (GBM) and other malignant tumours consist of heterogeneous cancer cells, including GBM-initiating cells (GICs). This heterogeneity is likely to arise from the following: different sets of genetic mutations and epigenetic modifications, which GICs gain in the transformation process; differences in cells of origin, such as stem cells, precursor cells or differentiated cells; and the cancer microenvironment, in which GICs communicate with neural cells, endothelial cells and immune cells. Furthermore, considering that various types of GICs can be generated at different time points of the transformation process, GBM very likely consists of heterogeneous GICs and their progeny. Because cancer cell heterogeneity is responsible for therapy resistance, it is crucial to develop methods of reducing such heterogeneity. Here, I summarize how GIC heterogeneity is generated in the transformation process and present how cell heterogeneity in cancer can be addressed based on recent findings.

Open reading frame mining identifies a TLR4 binding domain in the primary sequence of ECRG4

The embedding of small peptide ligands within large inactive pre-pro-precursor proteins encoded by orphan open reading frames (ORFs) makes them difficult to identify and study. To address this problem, we generated oligonucleotide (< 100-400 base pair) combinatorial libraries from either the epidermal growth factor (EGF) ORF that encodes the > 1200 amino acid EGF precursor protein or the orphan ECRG4 ORF, that encodes a 148 amino acid Esophageal Cancer Related Gene 4 (ECRG4), a putative cytokine precursor protein of up to eight ligands. After phage display and 3-4 rounds of biopanning for phage internalization into prostate cancer epithelial cells, sequencing identified the 53-amino acid EGF ligand encoded by the 5' region of the EGF ORF and three distinct domains within the primary sequence of ECRG4: its membrane targeting hydrophobic signal peptide, an unanticipated amino terminus domain at ECRG437-63 and a C-terminus ECRG4133-148 domain. Using HEK-blue cells transfected with the innate immunity receptor complex, we show that both ECRG437-63 and ECRG4133-148 enter cells by interaction with the TLR4 immune complex but neither stimulate NFkB. Taken together, the results help establish that phage display can be used to identify cryptic domains within ORFs of the human secretome and identify a novel TLR4-targeted internalization domain in the amino terminus of ECRG4 that may contribute to its effects on cell migration, immune cell activation and tumor suppression.

Potential functions of esophageal cancer-related gene-4 in the cardiovascular system

Esophageal cancer-related gene-4 (Ecrg4) is cloned from the normal epithelium of the esophagus. It is constitutively expressed in quiescent epithelial cells and downregulated during tumorigenesis, and Ecrg4 expression levels are inversely correlated with the malignant phenotype of tumor cells, validating that Ecrg4 is a real tumor suppressor gene. Unlike other tumor suppressor genes that usually encode membrane or intracellular proteins, Ecrg4 encodes a 148-amino acid pre-pro-peptide that is tethered on the cell surface in epithelial cells, specialized epithelial cells, and human leukocytes, where it can be processed tissue dependently into several small peptides upon cell activation. Ecrg4 is expressed in a wide variety of other cells/tissues, including cardiomyocytes and conduction system of the heart, the glomus cells of the carotid body, adrenal glands, choroid plexus, and leukocytes among others, where it exerts distinct functions, such as promoting/suppressing inflammation, inducing neuron senescence, stimulating the hypothalamus-pituitary-adrenal axis, maintaining the stemness of stem cells, participating in the rhythm and rate control of the heart, and possibly gauging the responsiveness of the cardiovascular system (CVS) to hypoxia, in addition to tumor suppression. Here, we briefly review the latest discoveries on Ecrg4 and its underlying molecular mechanisms as a tumor suppressor and focus on the emerging roles of Ecrg4 in the CVS.

Esophageal cancer related gene-4 inhibits the migration and proliferation of oral squamous cell carcinoma through BC200 lncRNA/MMP-9 and -13 signaling pathway

Esophageal cancer related gene-4 (ECRG4) inhibits the malignant phenotype of oral squamous cell carcinoma. However, the molecular mechanisms remain to be explored. Using the tongue carcinoma cell line, TCA8113 as a cell model, we showed that forced expression of ECRG4 down-regulated the expression of the BC200 long non-coding RNA (lncRNA) and matrix metalloproteinases (MMP-9 and MMP-13). Restoration of BC200 lncRNA rescued ECRG4-mediated down-regulation of MMP-9 and -13. Furthermore, over-expression of Ecrg4 inhibited cell proliferation and migration, which was abolished by forced expression of BC200 lncRNA in TCA8113 cells. Our results indicate that ECRG4 inhibits the malignant phenotype of TCA8113 cells most likely through suppression of BC200 lncRNA/MMPs signaling pathway, rationalizing that BC200 lncRNA may be a potential target for oral squamous cell carcinoma (OSCC) therapy.

Ecrg4 deficiency extends the replicative capacity of neural stem cells in a Foxg1-dependent manner

The self-renewal activity of neural stem cells (NSCs) has been suggested to decrease with aging, resulting in age-dependent declines in brain function, such as presbyopia and memory loss. The molecular mechanisms underlying decreases in NSC proliferation with age need to be elucidated in more detail to develop treatments that promote brain function. We have previously reported that the expression of esophageal cancer-related gene 4 (Ecrg4) was upregulated in aged NSCs, whereas its overexpression decreased NSC proliferation, suggesting a functional relationship between Ecrg4 and NSC aging. Using Ecrg4-deficient mice in which the Ecrg4 locus was replaced with the lacZ gene, we here show that Ecrg4 deficiency recovered the age-dependent decline in NSC proliferation and enhanced spatial learning and memory in the Morris water-maze paradigm. We demonstrate that the proliferation of Ecrg4-deficient NSCs was partly maintained by the increased expression of Foxg1. Collectively, these results determine Ecrg4 as a NSC aging factor.

Collateral Damage: What Effect Does Anti-CD4 and Anti-CD8α Antibody-Mediated Depletion Have on Leukocyte Populations?

Anti-CD4 or anti-CD8α Ab-mediated depletion strategies are widely used to determine the role of T cell subsets. However, surface expression of CD4 and CD8α is not limited to T cells and occurs on other leukocyte populations as well. Using both unbiased t-distributed stochastic neighbor embedding of flow cytometry data and conventional gating strategies, we assessed the impact of anti-CD4 and anti-CD8α Ab-mediated depletion on non-T cell populations in mice. Our results show that anti-CD4 and anti-CD8α Ab injections not only resulted in depletion of T cells but also led to depletion of specific dendritic cell subsets in a dose-dependent manner. Importantly, the extent of this effect varied between mock- and virus-infected mice. We also demonstrate the importance of using a second, noncompeting Ab (clone CT-CD8α) to detect CD8α⁺ cells following depletion with anti-CD8α Ab clone 2.43. Our study provides a necessary caution to carefully consider the effects on nontarget cells when using Ab injections for leukocyte depletion in all experimental conditions.

ECRG4: a new potential target in precision medicine

Given the rapid development in precision medicine, tremendous efforts have been devoted to discovering new biomarkers for disease diagnosis and treatment. Esophageal cancer-related gene-4 (ECRG4), which is initially known as a new candidate tumor suppressor gene, is emerging as a sentinel molecule for gauging tissue homeostasis. ECRG4 is unique in its cytokine-like functional pattern and epigenetically-regulated gene expression pattern. The gene can be released from the cell membrane upon activation and detected in liquid biopsy, thus offering considerable potential in precision medicine. This review provides an updated summary on the biology of ECRG4, with emphasis on its important roles in cancer diagnosis and therapy. The future perspectives of ECRG4 as a potential molecular marker in precision medicine are also discussed in detail.

Serum exosomes contain ECRG4 mRNA that suppresses tumor growth via inhibition of genes involved in inflammation, cell proliferation, and angiogenesis

Esophageal cancer related gene-4 (Ecrg4) has been shown to be a tumor suppressor in many organs. Exosomes are naturally secreted nanosized particles that carry signal molecules including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and messenger RNAs (mRNAs) among others. Upon internalization, exosomes unload their cargos that in turn modulate the biology of the recipient cells. Mounting evidence has shown that exosomal miRNAs are functional. However, reports that exosomes carry functional mRNAs remain scarce. We found that serum exosomes contain ECRG4 open reading frame. To simulate serum exosomal ECRG4, stable cell line expressing ECRG4 was created, from which exosomes were isolated and characterized, and the internalization and the resulting biological effects of exosomal ECRG4 were evaluated. Results showed that serum exosomes contain higher levels of ECRG4 mRNA in healthy individuals than their cancer counterparts. Exosomal ECRG4 can be internalized and unload the encapsulated ECRG4 into recipient cells, which subsequently suppressed cell proliferation in vitro, and inhibited tumor growth in a xenograft mouse model. Mechanistically, ECRG4-containing exosomes, when internalized, suppressed the expression of genes commonly implicated in inflammation, cell proliferation, and angiogenesis. Given that exosome is an ideal vehicle for therapeutics delivery and that ECRG4 is a tumor suppressor gene, the exosomal ECRG4 can be exploited as a formulation for cancer gene therapy.

Ecrg4 peptide is the ligand of multiple scavenger receptors

Esophageal cancer-related gene 4 (Ecrg4) encodes a hormone-like peptide that is believed to be involved in a variety of physiological phenomena, including tumour suppression. Recent progress in the study of Ecrg4 has shown that Ecrg4 is a proinflammatory factor and induces the expression of several cytokines and chemokines in macrophages/microglia. However, the detailed molecular mechanisms of Ecrg4 signalling, especially the Ecrg4 receptors, remain poorly understood. Here, using retrovirus-mediated expression cloning, we identified lectin-like oxidised low-density lipoprotein receptor-1 (LOX-1) as a membrane protein that binds amino acid residues 71–132 of Ecrg4 (Ecrg4(71–132)). Moreover, in addition to LOX-1, several scavenger receptors, such as Scarf1, Cd36 and Stabilin-1, facilitated the efficient internalisation of Ecrg4(71–132) into cells. A broad competitive inhibitor of scavenger receptors, polyinosinic acid, reduced both the binding of Ecrg4(71–132) and the activation of NF-κB in microglia. This activation was dependent on MyD88, an adaptor protein that recruits signalling proteins to Toll-like receptors (TLRs), with the consequent induction of various immune responses. These data suggest that multiple scavenger receptors recognise Ecrg4(71–132) and transduce its signals, together with TLRs, in microglia.