Cloning the genes and DNA binding properties of High Mobility Group B1 (HMGB1) proteins from the human blood flukes Schistosoma mansoni and Schistosoma japonicum

From Inflammation to Fibrosis: Novel Insights into the Roles of High Mobility Group Protein Box 1 in Schistosome-Induced Liver Damage

Schistosomiasis is a chronic helminthic disease of both humans and animals and the second most prevalent parasitic disease after malaria. Through a complex migration process, schistosome eggs trapped in the liver can lead to the formation of granulomas and subsequent schistosome-induced liver damage, which results in high mortality and morbidity. Although praziquantel can eliminate mature worms and prevent egg deposition, effective drugs to reverse schistosome-induced liver damage are scarce. High mobility group box 1 (HMGB1) is a multifunctional cytokine contributing to liver injury, inflammation, and immune responses in schistosomiasis by binding to cell-surface Toll-like receptors and receptors for advanced glycation end products. HMGB1 is increased in the serum of patients with schistosomiasis and enables hepatic stellate cells to adopt a proliferative myofibroblast-like phenotype, which is crucial to schistosome-induced granuloma formation. Inhibition of HMGB1 was found to generate protective responses against fibrotic diseases in animal models. Clinically, HMGB1 presents a potential target for treatment of the chronic sequelae of schistosomiasis. Here, the pivotal role of HMGB1 in granuloma formation and schistosome-induced liver damage, as well the potential of HMGB1 as a therapeutic target, are discussed.

Molecular and functional characterization of single-box high-mobility group B (HMGB) chromosomal protein from Aedes aegypti

High-mobility group B (HMGB) proteins have highly conserved, unique DNA-binding domains, HMG boxes, that can bind non-B-type DNA structures, such as bent, kinked and unwound structures, with high affinity. HMGB proteins also promote DNA bending, looping and unwinding. In this study, we determined the role of the Aedes aegypti single HMG-box domain protein AaHMGB; characterized its structure, spatiotemporal expression levels, subcellular localization, and nucleic acid binding activities; and compared these properties with those of its double-HMG-box counterpart protein, AaHMGB1. Via qRT-PCR, we showed that AaHMGB is expressed at much higher levels than AaHMGB1 throughout mosquito development. In situ hybridization results suggested a role for AaHMGB and AaHMGB1 during embryogenesis. Immunolocalization in the midgut revealed that AaHMGB is exclusively nuclear. Circular dichroism and fluorescence spectroscopy analyses showed that AaHMGB exhibits common features of α-helical structures and is more stably folded than AaHMGB1, likely due to the presence of one or two HMG boxes. Using several DNA substrates or single-stranded RNAs as probes, we observed significant differences between AaHMGB and AaHMGB1 in terms of their binding patterns, activity and/or specificity. Importantly, we showed that the phosphorylation of AaHMGB plays a critical role in its DNA-binding activity. Our study provides additional insight into the roles of single- versus double-HMG-box-containing proteins in nucleic acid interactions for better understanding of mosquito development, physiology and homeostasis.

Trypanosoma cruzi High Mobility Group B (TcHMGB) can act as an inflammatory mediator on mammalian cells

Background

High Mobility Group B (HMGB) proteins are nuclear architectural factors involved in chromatin remodeling and important nuclear events. HMGBs also play key roles outside the cell acting as alarmins or Damage-associated Molecular Patterns (DAMPs). In response to a danger signal these proteins act as immune mediators in the extracellular milieu. Moreover, these molecules play a central role in the pathogenesis of many autoimmune and both infectious and sterile inflammatory chronic diseases.

Principal findings

We have previously identified a High mobility group B protein from Trypanosoma cruzi (TcHMGB) and showed that it has architectural properties interacting with DNA like HMGBs from other eukaryotes. Here we show that TcHMGB can be translocated to the cytoplasm and secreted out of the parasite, a process that seems to be stimulated by acetylation. We report that recombinant TcHMGB is able to induce an inflammatory response in vitro and in vivo, evidenced by the production of Nitric Oxide and induction of inflammatory cytokines like TNF-α, IL-1β and IFN-γ gene expression. Also, TGF-β and IL-10, which are not inflammatory cytokines but do play key roles in Chagas disease, were induced by rTcHMGB.

Conclusions

These preliminary results suggest that TcHMGB can act as an exogenous immune mediator that may be important for both the control of parasite replication as the pathogenesis of Chagas disease and can be envisioned as a pathogen associated molecular pattern (PAMP) partially overlapping in function with the host DAMPs.

When an infection occurs, the innate immune cells recognize Pathogen Associated Molecular Patterns (PAMPs) through their Pattern Recognition Receptors. This triggers an inflammatory response intended to kill the foreign microbe. But inflammation can also be triggered by the recognition of endogenous molecules called “Danger (or Damage) Associated Molecular Patterns” (DAMPs) that are released by damaged or necrotic cells to “ring the alarm” of the immune system that repair is needed, so some of them are also known as “alarmins”. High Mobility group box 1 protein (HMGB1) is a prototypical alarmin molecule released by injured cells and it is also actively secreted by cells of the innate immune system in response to invasion as well as to sterile damage. Trypanosoma cruzi, the causal agent of Chagas Disease, has its own HMGB protein that we called TcHMGB. Using in vitro and in vivo experimental systems, we demonstrated for the first time that TcHMGB is able to mediate inflammation on mammalian cells, inducing the expression of both pro-inflammatory and anti-inflammatory cytokines. Our results suggest that the parasite´s protein could have a role in the immune response and the pathogenesis of Chagas disease, probably overlapping to some extent with the host cell DAMP molecules´ functions.

The DNA chaperone HMGB1 potentiates the transcriptional activity of Rel1A in the mosquito Aedes aegypti

High Mobility Group protein 1 (HMGB1) is a non-histone, chromatin-associated nuclear protein that functions in regulating eukaryotic gene expression. We investigated the influence and mechanism of action of Aedes aegypti HMGB1 (AaHMGB1) on mosquito Rel1A-mediated transcription from target gene promoters. The DNA-binding domain (RHD) of AaRel1A was bacterially expressed and purified, and AaHMGB1 dramatically enhanced RHD binding to consensus NF-kB/Rel DNA response elements. Luciferase reporter analyses using a cecropin gene promoter showed that AaHMGB1 potentiates the transcriptional activity of AaRel1A in Aag-2 cells. Moreover, overexpression of AaHMGB1 in Aag-2 cells led to an increase in mRNA levels of antimicrobial peptide genes. In vitro GST pull-down assays revealed that the presence of DNA is a pre-requisite for assembly of a possible ternary complex containing DNA, AaHMGB1 and AaRel1A. Notably, DNA bending by AaHMGB1 enhanced the binding of AaRel1A to a DNA fragment containing a putative NF-kB/Rel response element. Importantly, AaHMGB1 was identified as a potential immune modulator in A. aegypti through AaHMGB1 overexpression or RNAi silencing in Aag-2 cells followed by bacterial challenge or through AaHMGB1 RNAi knockdown in mosquitoes followed by Dengue virus (DENV) infection. We propose a model in which AaHMGB1 bends NF-kB/Rel target DNA to recruit and allow more efficient AaRel1A binding to activate transcription of effector genes, culminating in a stronger Toll pathway-mediated response against DENV infection.

The distinct C-terminal acidic domains of HMGB proteins are functionally relevant in Schistosoma mansoni

The Schistosoma mansoni High Mobility Group Box (HMGB) proteins SmHMGB1, SmHMGB2 and SmHMGB3 share highly conserved HMG box DNA binding domains but have significantly different C-terminal acidic tails. Here, we used three full-length and tailless forms of the S. mansoni HMGB proteins to examine the functional roles of their acidic tails. DNA binding assays revealed that the different lengths of the acidic tails among the three SmHMGB proteins significantly and distinctively influenced their DNA transactions. Spectroscopic analyses indicated that the longest acidic tail of SmHMGB3 contributes to the structural stabilisation of this protein. Using immunohistochemical analysis, we showed distinct patterns of SmHMGB1, SmHMGB2 and SmHMGB3 expression in different tissues of adult worms. RNA interference approaches indicated a role for SmHMGB2 and SmHMGB3 in the reproductive system of female worms, whereas for SmHMGB1 no clear phenotype was observed. Schistosome HMGB proteins can be phosphorylated, acetylated and methylated. Importantly, the acetylation and methylation of schistosome HMGBs were greatly enhanced upon removal of the acidic tail. These data support the notion that the C-terminal acidic tails dictate the differences in the structure, expression and function of schistosome HMGB proteins.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Protective Effects of Berberine on Isoproterenol-Induced Acute Myocardial Ischemia in Rats through Regulating HMGB1-TLR4 Axis

Berberine, an isoquinoline alkaloid originally isolated from the Chinese herb Coptis chinensis (Huanglian), has been shown to display a wide array of pharmacological activities. The present study was to investigate the effects of berberine against myocardial ischemia produced in rats by isoproterenol. 50 male Sprague-Dawley rats were randomized equally into five groups: a control group, an untreated model group, berberine (30, 60 mg/kg) treatment, or propranolol (30 mg/kg). Rats were treated for 12 days and then given isoproterenol, 85 mg/kg for 2 consecutive days by subcutaneous injection. ST-segment elevation was measured after the last administration. Serum levels of creatine kinase isoenzyme (CK-MB), lactate dehydrogenase (LDH), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were measured after the rats were sacrificed. The hearts were excised for determining heart weight index, microscopic examination, high mobility group box 1 (HMGB1), toll-like receptor (TLR4), prodeath protein (Bax), antideath protein (Bcl-2), and tumor necrosis factor (TNF-α) protein were determined by western blot. Berberine decreased the ST elevation induced by acute myocardial ischemia, and decreased serum levels of CK-MB, LDH, TNF-α, and IL-6. Berberine increased total superoxide dismutase (T-SOD) activity and decreased malondialdehyde (MDA) content in myocardial tissue. Berberine can regulate HMGB1-TLR4 axis to protect myocardial ischemia.

A nuclear factor of high mobility group box protein in Toxoplasma gondii

High mobility group box 1 (HMGB1) is a nuclear factor that usually binds DNA and modulates gene expression in multicellular organisms. Three HMGB1 orthologs were predicted in the genome of Toxoplasma gondii, an obligate intracellular protozoan pathogen, termed TgHMGB1a, b and c. Phylogenetic and bioinformatic analyses indicated that these proteins all contain a single HMG box and which shared in three genotypes. We cloned TgHMGB1a, a 33.9 kDa protein that can stimulates macrophages to release TNF-α, and, we demonstrated that the TgHMGB1a binds distorted DNA structures such as cruciform DNA in electrophoretic mobility shift assays (EMSA). Immunofluorescence assay indicated TgHMGB1a concentrated in the nucleus of intracellular tachyzoites but translocated into the cytoplasm while the parasites release to extracellular. There were no significant phenotypic changes when the TgHMGB1a B box was deleted, while transgenic parasites that overexpressed TgHMGB1a showed slower intracellular growth and caused delayed death in mouse, further quantitative RT-PCR analyses showed that the expression levels of many important genes, including virulence factors, increased when TgHMGB1a was overexpressed, but no significant changes were observed in TgHMGB1a B box-deficient parasites. Our findings demonstrated that TgHMGB1a is indeed a nuclear protein that maintains HMG box architectural functions and is a potential proinflammatory factor during the T.gondii infection. Further studies that clarify the functions of TgHMGB1s will increase our knowledge of transcriptional regulation and parasite virulence, and might provide new insight into host-parasite interactions for T. gondii infection.

The HMGB1-TLR4 axis contributes to myocardial ischemia/reperfusion injury via regulation of cardiomyocyte apoptosis

Toll-like receptor 4 (TLR4) and its ligand high mobility group box 1 (HMGB1), are known for playing central roles in ischemia-reperfusion injury in myocardium. However, the detailed mechanisms of TLR4 and HMGB1 are not fully understood. The aim of this study was to investigate the effects and possible mechanisms of the HMGB1-TLR4 axis and cardiomyocyte apoptosis on myocardial ischemic damage. Artificial oxygen ventilated anesthetized C3H/HeN mice and C3H/HeJ mice were subjected to 30 min of left anterior descending coronary artery occlusion followed by 6h of reperfusion. The myocardial infarct size, HMGB1 levels, apoptosis index, Bax, Bcl-2 and TNF-α mRNA levels were assessed. The results showed that a lowered amount of cardiomyocyte apoptosis and infarct size in the myocardium of TLR4-mutant mice after myocardial I/R and that TLR4 deficiency notably inhibited the expression of HMGB1 and TNF-a, both of which were up-regulated by ischemia/reperfusion. These findings suggest that the HMGB1-TLR4 axis plays a pathogenic role in triggering cardiomyocyte apoptosis during myocardial I/R injury and that the possible mechanism for this process is the result of released cytokines and inflammatory response involved in the HMGB1/TLR4-related pathway.

HMGB in mollusk Crassostrea ariakensis Gould: structure, pro-inflammatory cytokine function characterization and anti-infection role of its antibody

BACKGROUND

Crassostrea ariakensis Gould is a representative bivalve species and an economically important oyster in China, but suffers severe mortalities in recent years that are caused by rickettsia-like organism (RLO). Prevention and control of this disease is a priority for the development of oyster aquaculture. It has been proven that mammalian HMGB (high mobility group box) can be released extracellularly and acts as an important pro-inflammatory cytokine and late mediator of inflammatory reactions. In vertebrates, HMGB's antibody (anti-HMGB) has been shown to confer significant protection against certain local and systemic inflammatory diseases. Therefore, we investigated the functions of Ca-HMGB (oyster HMGB) and anti-CaHMGB (Ca-HMGB's antibody) in oyster RLO/LPS (RLO or LPS)-induced disease or inflammation.

METHODOLOGY/PRINCIPAL FINDINGS

Sequencing analysis revealed Ca-HMGB shares conserved structures with mammalians. Tissue-specific expression indicates that Ca-HMGB has higher relative expression in hemocytes. Significant continuous up-regulation of Ca-HMGB was detected when the hemocytes were stimulated with RLO/LPS. Recombinant Ca-HMGB protein significantly up-regulated the expression levels of some cytokines. Indirect immunofluorescence study revealed that Ca-HMGB localized both in the hemocyte nucleus and cytoplasm before RLO challenge, but mainly in the cytoplasm 12 h after challenge. Western blot analysis demonstrated Ca-HMGB was released extracellularly 4-12 h after RLO challenge. Anti-CaHMGB was added to the RLO/LPS-challenged hemocyte monolayer and real-time RT-PCR showed that administration of anti-CaHMGB dramatically reduced the rate of RLO/LPS-induced up-regulation of LITAF at 4-12 h after treatment. Flow cytometry analysis indicated that administration of anti-CaHMGB reduced RLO/LPS-induced hemocyte apoptosis and necrosis rates.

CONCLUSIONS/SIGNIFICANCE

Ca-HMGB can be released extracellularly and its subcellular localization varies when stimulated with RLO. Ca-HMGB is involved in oyster immune reactions and functions as a pro-inflammatory cytokine. Anti-CaHMGB can significantly suppress RLO/LPS-induced inflammatory responses and hemocyte necrosis and apoptosis, suggesting that Ca-HMGB is a potential target to prevent and control RLO/LPS-induced disease or inflammation.

High mobility group [corrected] box 1 mediates neutrophil recruitment in myocardial ischemia-reperfusion injury through toll like receptor 4-related pathway

This study aimed to explore the role of high mobility group [corrected] box 1 (HMGB1) and its receptor toll like receptor 4 (TLR4) on neutrophils in myocardial ischemia reperfusion (I/R) injury. We constructed TLR4-mutant (C3H/HeJ) and control (C3H/HeN) mouse models of myocardial I/R injury and subjected the mice to 30 min of ischemia and 6h of reperfusion. Light microscope was used to observe structural changes in the myocardium. HMGB1 levels were measured using quantitative real-time PCR and immunohistochemistry. Neutrophil accumulation, TNF-a expression and IL-8 levels were analyzed via myeloperoxidase (MPO) biochemical studies, quantitative real-time PCR and ELISA, respectively. The results demonstrated that fewer neutrophils infiltrated in the myocardium of TLR4-mutant mice after myocardial I/R and that TLR4 deficiency markedly decreased the ischemic injury caused by ischemia/reperfusion, and inhibited the expression of HMGB1, TNF-a, and IL-8, all of which were up-regulated by ischemia/reperfusion. These findings suggest that HMGB1 plays a central role in recruiting neutrophils during myocardial I/R leading to worsened myocardial I/R injury. This recruitment mechanism is possibly due to its inflammatory and chemokine functions based on the TLR4-dependent pathway.

The dengue vector Aedes aegypti contains a functional high mobility group box 1 (HMGB1) protein with a unique regulatory C-terminus

The mosquito Aedes aegypti can spread the dengue, chikungunya and yellow fever viruses. Thus, the search for key molecules involved in the mosquito survival represents today a promising vector control strategy. High Mobility Group Box (HMGB) proteins are essential nuclear factors that maintain the high-order structure of chromatin, keeping eukaryotic cells viable. Outside the nucleus, secreted HMGB proteins could alert the innate immune system to foreign antigens and trigger the initiation of host defenses. In this work, we cloned and functionally characterized the HMGB1 protein from Aedes aegypti (AaHMGB1). The AaHMGB1 protein typically consists of two HMG-box DNA binding domains and an acidic C-terminus. Interestingly, AaHMGB1 contains a unique alanine/glutamine-rich (AQ-rich) C-terminal region that seems to be exclusive of dipteran HMGB proteins. AaHMGB1 is localized to the cell nucleus, mainly associated with heterochromatin. Circular dichroism analyses of AaHMGB1 or the C-terminal truncated proteins revealed α-helical structures. We showed that AaHMGB1 can effectively bind and change the topology of DNA, and that the AQ-rich and the C-terminal acidic regions can modulate its ability to promote DNA supercoiling, as well as its preference to bind supercoiled DNA. AaHMGB1 is phosphorylated by PKA and PKC, but not by CK2. Importantly, phosphorylation of AaHMGB1 by PKA or PKC completely abolishes its DNA bending activity. Thus, our study shows that a functional HMGB1 protein occurs in Aedes aegypt and we provide the first description of a HMGB1 protein containing an AQ-rich regulatory C-terminus.

CK2 phosphorylation of Schistosoma mansoni HMGB1 protein regulates its cellular traffic and secretion but not its DNA transactions

Background

The helminth Schistosoma mansoni parasite resides in mesenteric veins where fecundated female worms lay hundred of eggs daily. Some of the egg antigens are trapped in the liver and induce a vigorous granulomatous response. High Mobility Group Box 1 (HMGB1), a nuclear factor, can also be secreted and act as a cytokine. Schistosome HMGB1 (SmHMGB1) is secreted by the eggs and stimulate the production of key cytokines involved in the pathology of schistosomiasis. Thus, understanding the mechanism of SmHMGB1 release becomes mandatory. Here, we addressed the question of how the nuclear SmHMGB1 can reach the extracellular space.

Principal Findings

We showed in vitro and in vivo that CK2 phosphorylation was involved in the nucleocytoplasmic shuttling of SmHMGB1. By site-directed mutagenesis we mapped the two serine residues of SmHMGB1 that were phosphorylated by CK2. By DNA bending and supercoiling assays we showed that CK2 phosphorylation of SmHMGB1 had no effect in the DNA binding activities of the protein. We showed by electron microscopy, as well as by cell transfection and fluorescence microscopy that SmHMGB1 was present in the nucleus and cytoplasm of adult schistosomes and mammalian cells. In addition, we showed that treatments of the cells with either a phosphatase or a CK2 inhibitor were able to enhance or block, respectively, the cellular traffic of SmHMGB1. Importantly, we showed by confocal microscopy and biochemically that SmHMGB1 is significantly secreted by S. mansoni eggs of infected animals and that SmHMGB1 that were localized in the periovular schistosomotic granuloma were phosphorylated.

Conclusions

We showed that secretion of SmHMGB1 is regulated by phosphorylation. Moreover, our results suggest that egg-secreted SmHMGB1 may represent a new egg antigen. Therefore, the identification of drugs that specifically target phosphorylation of SmHMGB1 might block its secretion and interfere with the pathogenesis of schistosomiasis.

Control of transcription in Schistosoma mansoni: chromatin remodeling and other regulatory elements

The platyhelminth parasite Schistosoma mansoni, the causative agent of schistosomiasis, is a dioecious parasite with a complex life cycle that includes two different hosts and two free-living stages. Yet very little is known about the biochemical details connected to these different transitions. In the present work, results will be presented showing the most recent results in S. mansoni regarding the characterization of transcription factors and coactivators that act directly on the transcriptional machinery and those that are involved with chromatin remodeling. It is hoped that the information gathered here may contribute towards the understanding of crucial events in the parasite life cycle. Likewise, the development of new drugs that could interfere with oogenesis and sexual maturation may eventually profit from the information contained herein.

Characterization of an Entamoeba histolytica high-mobility-group box protein induced during intestinal infection

The unicellular eukaryote Entamoeba histolytica is a human parasite that causes amebic dysentery and liver abscess. A genome-wide analysis of gene expression modulated by intestinal colonization and invasion identified an upregulated transcript that encoded a putative high-mobility-group box (HMGB) protein, EhHMGB1. We tested if EhHMGB1 encoded a functional HMGB protein and determined its role in control of parasite gene expression. Recombinant EhHMGB1 was able to bend DNA in vitro, a characteristic of HMGB proteins. Core conserved residues required for DNA bending activity in other HMGB proteins were demonstrated by mutational analysis to be essential for EhHMGB1 activity. EhHMGB1 was also able to enhance the binding of human p53 to its cognate DNA sequence in vitro, which is expected for an HMGB1 protein. Confocal microscopy, using antibodies against the recombinant protein, confirmed its nuclear localization. Overexpression of EhHMGB1 in HM1:IMSS trophozoites led to modulation of 33 transcripts involved in a variety of cellular functions. Of these, 20 were also modulated at either day 1 or day 29 in the mouse model of intestinal amebiasis. Notably, four transcripts with known roles in virulence, including two encoding Gal/GalNAc lectin light chains, were modulated in response to EhHMGB1 overexpression. We concluded that EhHMGB1 was a bona fide HMGB protein with the capacity to recapitulate part of the modulation of parasite gene expression seen during adaptation to the host intestine.