Regulation of DNA-dependent activities by the functional motifs of the high-mobility-group chromosomal proteins

HMGB1 induction of clusterin creates a chemoresistant niche in human prostate tumor cells

Development of chemoresistance, especially to docetaxel (DTX), is the primary barrier to the cure of castration-resistant prostate cancer but its mechanism is obscure. Here, we report a seminal crosstalk between dying and residual live tumor cells during treatment with DTX that can result in outgrowth of a chemoresistant population. Survival was due to the induction of secretory/cytoplasmic clusterin (sCLU), which is a potent anti-apoptotic protein known to bind and sequester Bax from mitochondria, to prevent caspase 3 activation. sCLU induction in live cells depended on HMGB1 release from dying cells. Supernatants from DTX-treated DU145 tumor cells, which were shown to contain HMGB1, effectively induced sCLU from newly-plated DU145 tumor cells and protected them from DTX toxicity. Addition of anti-HMBG1 to the supernatant or pretreatment of newly-plated DU145 tumor cells with anti-TLR4 or anti-RAGE markedly abrogated sCLU induction and protective effect of the supernatant. Mechanistically, HMGB1 activated NFκB to promote sCLU gene expression and prevented the translocation of activated Bax to mitochondria to block cell death. Importantly, multiple currently-used chemotherapeutic drugs could release HMGB1 from tumor cells. These results suggest that acquisition of chemoresistance may involve the HMGB1/TLR4-RAGE/sCLU pathway triggered by dying cells to provide survival advantage to remnant live tumor cells.

Functional interplay between histone H1 and HMG proteins in chromatin

The dynamic interaction of nucleosome binding proteins with their chromatin targets is an important element in regulating the structure and function of chromatin. Histone H1 variants and High Mobility Group (HMG) proteins are ubiquitously expressed in all vertebrate cells, bind dynamically to chromatin, and are known to affect chromatin condensation and the ability of regulatory factors to access their genomic binding sites. Here, we review the studies that focus on the interactions between H1 and HMGs and highlight the functional consequences of the interplay between these architectural chromatin binding proteins. H1 and HMG proteins are mobile molecules that bind to nucleosomes as members of a dynamic protein network. All HMGs compete with H1 for chromatin binding sites, in a dose dependent fashion, but each HMG family has specific effects on the interaction of H1 with chromatin. The interplay between H1 and HMGs affects chromatin organization and plays a role in epigenetic regulation.

High mobility group (HMG) proteins: Modulators of chromatin structure and DNA repair in mammalian cells

It has been almost a decade since the last review appeared comparing and contrasting the influences that the different families of High Mobility Group proteins (HMGA, HMGB and HMGN) have on the various DNA repair pathways in mammalian cells. During that time considerable progress has been made in our understanding of how these non-histone proteins modulate the efficiency of DNA repair by all of the major cellular pathways: nucleotide excision repair, base excision repair, double-stand break repair and mismatch repair. Although there are often similar and over-lapping biological activities shared by all HMG proteins, members of each of the different families appear to have a somewhat 'individualistic' impact on various DNA repair pathways. This review will focus on what is currently known about the roles that different HMG proteins play in DNA repair processes and discuss possible future research areas in this rapidly evolving field.

Role of high-mobility group box 1 in methamphetamine-induced activation and migration of astrocytes

Background

Mounting evidence has indicated that high-mobility group box 1 (HMGB1) is involved in cell activation and migration. Our previous study demonstrated that methamphetamine mediates activation of astrocytes via sigma-1 receptor (σ-1R). However, the elements downstream of σ-1R in this process remain poorly understood. Thus, we examined the molecular mechanisms involved in astrocyte activation and migration induced by methamphetamine.

Methods

The expression of HMGB1, σ-1R, and glial fibrillary acidic protein (GFAP) was examined by western blot and immunofluorescent staining. The phosphorylation of cell signaling pathways was detected by western blot, and cell migration was examined using a wound-healing assay in rat C6 astroglia-like cells transfected with lentivirus containing red fluorescent protein (LV-RFP) as well as in primary human astrocytes. The role of HMGB1 in astrocyte activation and migration was validated using a siRNA approach.

Results

Exposure of C6 cells to methamphetamine increased the expression of HMGB1 via the activation of σ-1R, Src, ERK mitogen-activated protein kinase, and downstream NF-κB p65 pathways. Moreover, methamphetamine treatment resulted in increased cell activation and migration in C6 cells and primary human astrocytes. Knockdown of HMGB1 in astrocytes transfected with HMGB1 siRNA attenuated the increased cell activation and migration induced by methamphetamine, thereby implicating the role of HMGB1 in the activation and migration of C6 cells and primary human astrocytes.

Conclusions

This study demonstrated that methamphetamine-mediated activation and migration of astrocytes involved HMGB1 up-regulation through an autocrine mechanism. Targeting HMGB1 could provide insights into the development of a potential therapeutic approach for alleviation of cell activation and migration of astrocytes induced by methamphetamine.

Functional compensation among HMGN variants modulates the DNase I hypersensitive sites at enhancers

DNase I hypersensitive sites (DHSs) are a hallmark of chromatin regions containing regulatory DNA such as enhancers and promoters; however, the factors affecting the establishment and maintenance of these sites are not fully understood. We now show that HMGN1 and HMGN2, nucleosome-binding proteins that are ubiquitously expressed in vertebrate cells, maintain the DHS landscape of mouse embryonic fibroblasts (MEFs) synergistically. Loss of one of these HMGN variants led to a compensatory increase of binding of the remaining variant. Genome-wide mapping of the DHSs in Hmgn1(-/-), Hmgn2(-/-), and Hmgn1(-/-)n2(-/-) MEFs reveals that loss of both, but not a single HMGN variant, leads to significant remodeling of the DHS landscape, especially at enhancer regions marked by H3K4me1 and H3K27ac. Loss of HMGN variants affects the induced expression of stress-responsive genes in MEFs, the transcription profiles of several mouse tissues, and leads to altered phenotypes that are not seen in mice lacking only one variant. We conclude that the compensatory binding of HMGN variants to chromatin maintains the DHS landscape, and the transcription fidelity and is necessary to retain wild-type phenotypes. Our study provides insight into mechanisms that maintain regulatory sites in chromatin and into functional compensation among nucleosome binding architectural proteins.

Sodium Butyrate Reduces Organ Injuries in Mice with Severe Acute Pancreatitis Through Inhibiting HMGB1 Expression

OBJECTIVE

The present study was designed to evaluate the effect of sodium butyrate on pancreas damage and to investigate the role of high-mobility group box-1 (HMGB1) and nuclear factor-κB (NF-κB) in the development of severe acute pancreatitis (SAP) in a mouse model.

METHODS

The SAP model was established by intraperitoneal injection of two doses of 20 % L-2 arginine (200 mg/g). Female Sprague-Dawley mice were randomly allocated into three groups (n = 48/group): the control, untreated SAP, and sodium butyrate-treated SAP groups. The animals were euthanized at 0, 12, 24, and 48 h after the establishment of the SAP. Histopathology of the pancreas was performed, and the NF-κB levels were determined by immunohistochemistry. The serum levels of tumor necrosis factor (TNFα), interleukin-6 (IL-6), and HMGB1 were measured by ELISA. The HMGB1 mRNA levels were determined by qRT-PCR.

RESULTS

The sodium butyrate-treated SAP animals showed significantly improved pancreas histopathology and lower serum amylase levels than the untreated SAP animals. In the SAP group, the mRNA levels of HMGB1 were remarkably increased at the 12 h, peaked at 24 h, and remained at a high level up to 48 h after L-2 arginine injection. The levels of TNFα and IL-6 were decreased at 48 h. Treatment with sodium butyrate reduced the pathological lesions, the serum levels of HMGB1, TNFα, and IL-6, the HMGB1 mRNA levels, and NF-κB activity.

CONCLUSION

Sodium butyrate inhibits the NF-κB activation and reduces pancreas injury in SAP through the modulation of HMGB1 and other inflammatory cytokine responses.

High-mobility group nucleosome-binding protein 1 is a novel clinical biomarker in non-small cell lung cancer

The involvement of alarmin high-mobility group nucleosome-binding protein 1 (HMGN1) in non-small cell lung cancer (NSCLC) is unknown. To address the presence of HMGN1 in the serum of different stages of NSCLC patients and healthy controls, we enrolled a consecutive sample of adult serum at diagnosis and correlated it with clinicopathologic outcomes. A total of 100 NSCLC patients and 23 healthy volunteers were enrolled from January 2012 through December 2013. Serum HMGN1 levels were determined by enzyme-linked immunosorbent assay (ELISA). Additionally, HMGN1 levels in 50 NSCLC patients with early-stage disease who received curative pneumonectomy were correlated with survivals. Kaplan-Meier plots were used to analyze the data. The patients with NSCLC were characterized by significantly higher serum levels of HMGN1 (0.4585 ± 0.0640 ng/ml) compared to those in healthy controls (0.3578 ± 0.0304 ng/ml). The serum HMGN1 levels were 0.4027 ± 0.0271 ng/ml, 0.4604 ± 0.0328 ng/ml, 0.5408 ± 0.0459 ng/ml, and 0.4213 ± 0.0341 ng/ml in patients with TNM stages I, II, IV, and IV, respectively (p < 0.001). There were significant differences among four groups (p < 0.001). Additionally, a positive correlation between serum HMGN1 and tumor stage was found in local disease, while serum HMGN1 level in metastatic NSCLC patients was significantly decreased. The Kaplan-Meier plots showed that patients with high serum HMGN1 had a poorer overall survival (OS) after curative pneumonectomy than those with low serum HMGN1 (p = 0.019). Inflammation triggered by alarmins plays a role in NSCLC pathogenesis. HMGN1 can serve as a useful clinical parameter for evaluating disease progression and predicting the outcomes for early-stage patients with NSCLC undergoing pneumonectomy.

Role of high-mobility group box 1 protein in inflammatory bowel disease

High-mobility group box 1 (HMGB1) protein is a nuclear non-histone DNA-binding protein. It is released into the extracellular milieu and mediates inflammatory responses, which contribute to the pathogenesis of numerous inflammatory diseases, including inflammatory bowel disease (IBD). An online search was performed in PubMed and Web of Science databases for articles providing evidence on the role of HMGB1 in IBD. HMGB1 plays an important role in IBD pathogenesis. Application of HMGB1 antagonists reduced inflammatory reactions and ameliorated colitis in rodent models, which may provide new insights into the diagnosis and treatment of IBD.

Circulating HMGB1 and RAGE as Clinical Biomarkers in Malignant and Autoimmune Diseases

High molecular group box 1 (HMGB1) is a highly conserved member of the HMG-box-family; abundantly expressed in almost all human cells and released in apoptosis; necrosis or by activated immune cells. Once in the extracellular space, HMGB1 can act as a danger associated molecular pattern (DAMP), thus stimulating or inhibiting certain functions of the immune system; depending on the “combinatorial cocktail” of the surrounding milieu. HMGB1 exerts its various functions through binding to a multitude of membrane-bound receptors such as TLR-2; -4 and -9; IL-1 and RAGE (receptor for advanced glycation end products); partly complex-bound with intracellular fragments like nucleosomes. Soluble RAGE in the extracellular space, however, acts as a decoy receptor by binding to HMGB1 and inhibiting its effects. This review aims to outline today’s knowledge of structure, intra- and extracellular functions including mechanisms of release and finally the clinical relevance of HMGB1 and RAGE as clinical biomarkers in therapy monitoring, prediction and prognosis of malignant and autoimmune disease.

Treatment of low molecular weight heparin inhibits systemic inflammation and prevents endotoxin-induced acute lung injury in rats

To determine whether low molecular weight heparin (LMWH) is able to reduce pulmonary inflammation and improve the survival in rats with endotoxin-induced acute lung injury (ALI). Rat ALI model was reproduced by injection of lipopolysaccharide (LPS) into tail vein. Rats were divided randomly into three groups: control group, ALI group, LMWH-treated group. Blood was collected and lung tissue was harvested at the designated time points for analysis. The lung specimens were harvested for morphological studies, streptavidin-peroxidase immunohistochemistry examination. Lung tissue edema was evaluated by tissue water content. The levels of lung tissue myeloperoxidase (MPO) were determined. Meanwhile, the nuclear factor-kappa B (NF-κB) activation, tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) levels and high mobility group box 1 (HMGB1) and intercellular adhesion molecule-1 (ICAM-1) protein levels in the lung were studied. In survival studies, a separate group of rats were treated with LMWH or sterile saline after LPS administration. Then, the mortality was recorded. Treatment with LMWH after ALI was associated with a reduction in the severity of LPS-induced lung injury. Treatment with LMWH significantly decreased the expression of TNF-α, IL-1β, HMGB1 and ICAM-1 in the lung of ALI rats. Similarly, treatment with LMWH dramatically diminished LPS-induced neutrophil sequestration and markedly reduced the enhanced lung permeability. In the present study, LMWH administration inhibited the nuclear translocation of NF-κB in the lung. Survival was significantly higher among the LMWH-treated group compared with the ALI group. These data suggest that LMWH attenuates inflammation and prevents lethality in endotoxemic rats.

Hijacked in cancer: the KMT2 (MLL) family of methyltransferases

Histone-lysine N-methyltransferase 2 (KMT2) family proteins methylate lysine 4 on the histone H3 tail at important regulatory regions in the genome and thereby impart crucial functions through modulating chromatin structures and DNA accessibility. Although the human KMT2 family was initially named the mixed-lineage leukaemia (MLL) family, owing to the role of the first-found member KMT2A in this disease, recent exome-sequencing studies revealed KMT2 genes to be among the most frequently mutated genes in many types of human cancers. Efforts to integrate the molecular mechanisms of KMT2 with its roles in tumorigenesis have led to the development of first-generation inhibitors of KMT2 function, which could become novel cancer therapies.

Emerging roles for HMGB1 protein in immunity, inflammation, and cancer

High-mobility group box 1 (HMGB1) protein is a member of the highly conserved non-histone DNA binding protein family. First identified in 1973, as one of a group of chromatin-associated proteins with high acidic and basic amino acid content, it was so named for its characteristic rapid mobility in polyacrylamide gel electrophoresis. HMGB1 was later discovered to have another function. It is released from a variety of cells into the extracellular milieu to act on specific cell-surface receptors. In this latter role, HMGB1 is a proinflammatory cytokine that may contribute to many inflammatory diseases, including sepsis. Therefore, HMGB1 regulates intracellular cascades influencing immune cell functions, including chemotaxis and immune modulation. The bioactivity of the HMGB1 is determined by specific posttranslational modifications that regulate its role in inflammation and immunity. During tumor development, HMGB1 has been reported to play paradoxical roles in promoting both cell survival and death by regulating multiple signaling pathways. In this review, we focus on the role of HMGB1 in physiological and pathological responses, as well as the mechanisms by which it contributes to immunity, inflammation, and cancer progression.

The compromise of macrophage functions by hyperoxia is attenuated by ethacrynic acid via inhibition of NF-κB-mediated release of high-mobility group box-1

The prolonged exposure to hyperoxia can compromise macrophage functions and contribute to the development of ventilator-associated pneumonia. High levels of extracellular high-mobility group box-1 (HMGB1) in the airways of mice exposed to hyperoxia can directly cause macrophage dysfunction. Hence, inhibition of the release of nuclear HMGB1 into the extracellular milieu may help to maintain macrophage functions under hyperoxic conditions. The present study investigates whether ethacrynic acid (EA) affects hyperoxia-induced HMGB1 release from macrophages and improves their functions. Macrophage-like RAW 264.7 cells and bone marrow-derived macrophages were exposed to different concentrations of EA for 24 hours in the presence of 95% O2. EA significantly decreased the accumulation of extracellular HMGB1 in cultured media. Importantly, the phagocytic activity and migration capability of macrophages were significantly enhanced in EA-treated cells. Interestingly, hyperoxia-induced NF-κB activation was also inhibited in these cells. To determine whether NF-κB plays a role in hyperoxia-induced HMGB1 release, BAY 11-7082, an inhibitor of NF-κB activation, was used. Similar to EA, BAY 11-7082 significantly inhibited the accumulation of extracellular HMGB1 and improved hyperoxia-compromised macrophage migration and phagocytic activity. Furthermore, 24-hour hyperoxic exposure of macrophages caused hyperacetylation of HMGB1 and its subsequent cytoplasmic translocation and release, which were inhibited by EA and BAY 11-7082. Together, these results suggest that EA enhances hyperoxia-compromised macrophage functions by inhibiting HMGB1 hyperacetylation and its release from macrophages, possibly through attenuation of the NF-κB activation. Therefore, the activation of NF-κB could be one of the underlying mechanisms that mediate hyperoxia-compromised macrophage functions.

Low shear stress induced HMGB1 translocation and release via PECAM-1/PARP-1 pathway to induce inflammation response

Low shear stress (LSS) plays a critical role in the site predilection of atherosclerosis through activation of cellular mechanosensors, such as platelet endothelial cell adhesion molecule 1 (PECAM-1). Poly(ADP-ribose) polymerase 1 (PARP-1) is a nuclear enzyme that regulates the expression of various inflammatory cytokines. The nuclear enzyme high mobility group box 1 (HMGB1) can induce inflammation response by binding to toll-like receptor 4 (TLR4). In the present study, we aimed to investigate the role and mechanism of HMGB1 in LSS induced inflammation in human umbilical vein endothelial cells (HUVECs). HUVECs were stimulated by undisturbed shear stress (USS, 1 Pa) and LSS (0.4 Pa) in our experiments. Gene expression was inhibited by small interfering RNA (siRNA). ICAM-1 expression was regulated by LSS in a time dependent manner. LSS can induce HMGB1 translocation from nucleus to cytoplasm and release. Compared with the USS, LSS could increase the protein expression of PECAM-1 and PARP-1 as well as the secretion of TNF-α and IL-1β. LSS induced the translocation of HMGB1 from nucleus to cytoplasm. Inhibition of HGMB1 reduced LSS-induced inflammatory response. Inhibition of PARP-1 suppressed inflammatory response through inhibiting TLR4 expression and HMGB1 translocation. PECAM-1 inhibition reduced LSS-induced ICAM-1 expression, TNF-α and IL-1β secretion, and monocytes adhesion. LSS can induce inflammatory response via PECAM-1/PARP-1/HMGB1 pathway. PARP-1 plays a fundamental role in HMGB1 translocation and TLR4 expression. Inhibition of PARP-1 may shed light on the treatment of HMGB1 involved inflammation during atherosclerosis.

Nucleosome-binding protein HMGN2 exhibits antitumor activity in human SaO2 and U2-OS osteosarcoma cell lines

High mobility group N (HMGNs) are members of the high mobility group protein family, and are involved in the development and progression of several tumors. HMGN1 and HMGN5 were previously shown to be associated with the bioactivities of osteosarcoma. However, the effects and molecular mechanisms of HMGN2 on osteosarcoma progression remain to be determined. In order to characterize the endogenous expression of HMGN2 in osteosarcoma cell lines, RT-PCR and western blot analysis were performed. Recombinant HMGN2 lentivirus was used to infect the osteosarcoma cell lines with relatively low HMGN2 expression to determine the functional relevance of HMGN2 overexpression in osteosarcoma cell growth and migration in vitro and in vivo, and to investigate the expression levels of Ki-67, PCNA, cyclin D1 and cyclin E. The results showed that osteosarcoma cell proliferation and migration were significantly reduced by HMGN2, as indicated by cell count and wound-healing assays. Cell apoptosis was markedly induced and HMGN2 increased the sensitivity to chemotherapy. When HMGN2 expression was enhanced, the expression of cyclin D1 and PCNA was downregulated in osteosarcoma cells. In addition, the tumor volumes in SaO2 and U2-OS subcutaneous nude mouse models treated with HMGN2 lentivirus were significantly decreased as compared to those of the GFP group. These results suggested that the enhanced expression of HMGN2 in osteosarcoma cells by HMGN2 lentivirus, exerts inhibitory effects on growth and migration of osteosarcoma cells.

Alcohol exposure after mild focal traumatic brain injury impairs neurological recovery and exacerbates localized neuroinflammation

Traumatic brain injury (TBI) represents a leading cause of morbidity and mortality among young individuals. Alcohol abuse is a risk factor associated with increased TBI incidence. In addition, up to 26% of TBI patients engage in alcohol consumption after TBI. Limited preclinical studies have examined the impact of post-injury alcohol exposure on TBI recovery. The aim of this study was to determine the isolated and combined effects of TBI and alcohol on cognitive, behavioral, and physical recovery, as well as on associated neuroinflammatory changes. Male Sprague-Dawley rats (∼300g) were subjected to a mild focal TBI by lateral fluid percussion (∼30PSI, ∼25ms) under isoflurane anesthesia. On day 4 after TBI, animals were exposed to either sub-chronic intermittent alcohol vapor (95% ethanol 14h on/10h off; BAL∼200mg/dL) or room air for 10days. TBI induced neurological dysfunction reflected by an increased neurological severity score (NSS) showed progressive improvement in injured animals exposed to room air (TBI/air). In contrast, TBI animals exposed to alcohol vapor (TBI/alcohol) showed impaired NSS recovery throughout the 10-day period of alcohol exposure. Open-field exploration test revealed an increased anxiety-like behavior in TBI/alcohol group compared to TBI/air group. Additionally, alcohol-exposed animals showed decreased locomotion and impaired novel object recognition. Immunofluorescence showed enhanced reactive astrocytes, microglial activation, and HMGB1 expression localized to the injured cortex of TBI/alcohol as compared to TBI/air animals. The expression of neuroinflammatory markers showed significant positive correlation with NSS. These findings indicated a close relationship between accentuated neuroinflammation and impaired neurological recovery from post-TBI alcohol exposure. The clinical implications of long-term consequences in TBI patients exposed to alcohol during recovery warrant further investigation.

HMGB1 genetic polymorphisms in oral squamous cell carcinoma and oral lichen planus patients

OBJECTIVES

This study examined the single nucleotide polymorphisms (SNPs) in high-mobility group box 1 (HMGB1) gene in patients with oral squamous cell carcinoma (OSCC) and oral lichen planus (OLP).

MATERIALS AND METHODS

The study was conducted on 93 patients with OSCC, 53 patients with OLP, and 100 controls, all Caucasians of the same ethnicity, matched by age. HMGB1 genotypes for 4 SNPs, 2262G/A (rs1045411), 1177G/C (rs3742305), 3814C/G (rs2249825), and rs4540927, were assessed using TaqMan SNP Genotyping Assays, Applied Biosystems.

RESULTS

The HMGB1 1177GG genotype was associated with lymph-node metastasis and tumor stage in OSCCs (P = 0.016 and P = 0.030, respectively). Genotype 1177GG resulted in poorer recurrence-free survival (RFS), P = 0.000. The 1177G/C polymorphism was an independent predictor of RFS compared to GG genotype, P = 0.001. The three polymorphisms were in linkage disequilibrium (LD). The AGC and GGC haplotypes were associated with an increased oral cancer risk, determined over the haplotype odds ratios (HOR = 13.316, P = 0.015, and HOR = 5.769, P = 0.029, respectively). The AGC haplotype was related to erosive OLP progression to OSCC (HOR = 12.179, P = 0.001).

CONCLUSIONS

HMGB1 polymorphism 1177G/C could be associated with tumor progression and recurrence-free survival in patients with OSCC. The haplotypes of HMGB1 gene might be associated with susceptibility to OSCC and OLP progression to OSCC.

Cerebral vasospasm

Cerebral vasospasm causes delayed ischemic neurologic deficits after aneurysmal subarachnoid hemorrhage. This is a well-established clinical entity with significant associated morbidity and mortality. The underlying patholphysiology is highly complex and poorly understood. Large-vessel vasospasm, autoregulatory dysfunction, inflammation, genetic predispositions, microcirculatory failure, and spreading cortical depolarization are aspects of delayed neurologic deterioration that have been described in the literature. This article presents a perspective on cerebral vasospasm, as guided by the literature to date, specifically examining the mechanism, diagnosis, and treatment of cerebral vasospasm.

Chromatin decompaction by the nucleosomal binding protein HMGN5 impairs nuclear sturdiness

In most metazoan nuclei, heterochromatin is located at the nuclear periphery in contact with the nuclear lamina, which provides mechanical stability to the nucleus. We show that in cultured cells, chromatin de-compaction by the nucleosome binding protein HMGN5 decreases the sturdiness, elasticity, and rigidity of the nucleus. Mice overexpressing HMGN5, either globally or only in the heart, are normal at birth but develop hypertrophic heart with large cardiomyoctyes, deformed nuclei and disrupted lamina, and die of cardiac malfunction. Chromatin de-compaction is seen in cardiomyocytes of newborn mice but misshaped nuclei with disrupted lamina are seen only in adult cardiomyocytes, suggesting that loss of heterochromatin diminishes the ability of the nucleus to withstand the mechanical forces of the contracting heart. Thus, heterochromatin enhances the ability of the nuclear lamina to maintain the sturdiness and shape of the eukaryotic nucleus; a structural role for chromatin that is distinct from its genetic functions.

Gene expression disorders of innate antibacterial signaling pathway in pancreatic cancer patients: implications for leukocyte dysfunction and tumor progression

The study was carried out to investigate changes in gene expression of innate antibacterial signaling pathways in patients with pancreatic cancer. Expression of the following genes was measured in peripheral blood leukocytes of 55 patients with pancreatic adenocarcinoma using real-time polymerase chain reaction (RT-PCR): TLR4, NOD1, MyD88, TRAF6 and HMGB1. The levels of expression of TLR4, NOD1 and TRAF6 genes were significantly elevated (p = 0.007; p = 0.001 and p = 0.01, respectively), while MyD88 expression was markedly reduced (p = 0.0002), as compared to controls. Expression of TLR4 and NOD1 exceeded the normal level more than 3.5-fold and there was a significant correlation found between the expression of these genes (r = 0.558, p < 0.001). TLR4, NOD1 and MyD88 genes were expressed at a similar level both before and after surgery. No significant changes in the expression of HMGB1 gene were observed. The results of the study clearly indicate abnormal expression of genes belonging to innate antibacterial signaling pathways in peripheral blood leukocytes of patients with pancreatic cancer, which may lead to leukocyte dysfunction. Overexpression of TLR4, NOD1 and TRAF6 genes, and decreased MyD88 gene expression may contribute to chronic inflammation and tumor progression by up-regulation of the innate antibacterial response. The parameters tested are useful for monitoring innate immunity gene disorders and pancreatic cancer progression.

PARP-1 Mediates LPS-Induced HMGB1 Release by Macrophages through Regulation of HMGB1 Acetylation

The high-mobility group box protein 1 (HMGB1) is increasingly recognized as an important inflammatory mediator. In some cases, the release of HMGB1 is regulated by poly(ADP-ribose) polymerase-1 (PARP-1), but the mechanism is still unclear. In this study, we report that PARP-1 activation contributes to LPS-induced PARylation of HMGB1, but the PARylation of HMGB1 is insufficient to direct its migration from the nucleus to the cytoplasm; PARP-1 regulates the translocation of HMGB1 to the cytoplasm through upregulating the acetylation of HMGB1. In mouse bone marrow–derived macrophages, genetic and pharmacological inhibition of PARP-1 suppressed LPS-induced translocation and release of HMGB1. Increased PARylation was accompanied with the nucleus-to-cytoplasm translocation and release of HMGB1 upon LPS exposure, but PARylated HMGB1 was located at the nucleus, unlike acetylated HMGB1 localized at the cytoplasm in an import assay. PARP inhibitor and PARP-1 depletion decreased the activity ratio of histone acetyltransferases to histone deacetylases that elevated after LPS stimulation and impaired LPS-induced acetylation of HMGB1. In addition, PARylation of HMGB1 facilitates its acetylation in an in vitro enzymatic reaction. Furthermore, reactive oxygen species scavenger (N-acetyl-l-cysteine) and the ERK inhibitor (FR180204) impaired LPS-induced PARP activation and HMGB1 release. Our findings suggest that PARP-1 regulates LPS-induced acetylation of HMGB1 in two ways: PARylating HMGB1 to facilitate the latter acetylation and increasing the activity ratio of histone acetyltransferases to histone deacetylases. These studies revealed a new mechanism of PARP-1 in regulating the inflammatory response to endotoxin.

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.

Evidence for necrosis, but not apoptosis, in human hepatoma cells with knockdown of mitochondrial aquaporin-8

We previously found that mitochondrial aquaporin-8 (mtAQP8) channels facilitate mitochondrial H2O2 release in human hepatoma HepG2 cells and that their knockdown causes oxidant-induced mitochondrial dysfunction and loss of viability. Here, we studied whether apoptosis or necrosis is involved as the mode of cell death. We confirmed that siRNA-induced mtAQP8 knockdown significantly decreased HepG2 viability by MTT assay, LDH leakage, and trypan blue exclusion test. Analysis of mitochondrial proapoptotic Bax-to-antiapoptotic BclXL ratio, mitochondrial cytochrome c release and caspase-3 activation showed no alterations in mtAQP8-knockdown cells. This indicates a primary mechanism of cell death other than the intrinsic mitochondrial apoptotic pathway. Thus, nuclear staining with DAPI did not reveal any increase of apoptotic features, i.e. chromatin condensation or nuclear fragmentation. Flow cytometry studies after double cell staining with annexin V and propidium iodide confirmed lack of apoptosis and suggested necrosis as the primary mechanism of death in mtAQP8-knockdown HepG2 cells. Necrosis was further supported by the increased nuclear delocalization and extracellular release of the High Mobility Group Box 1 protein. The knockdown of mtAQP8 in another human hepatoma-derived cell line, i.e. HuH-7 cells, also induced necrotic but not apoptotic death. Our data suggest that mtAQP8 knockdown induces necrotic cell death in human neoplastic hepatic cells, a finding that might be relevant to therapeutic strategies against hepatoma cells.

Anti-inflammative effect of glycyrrhizin on rat thermal injury via inhibition of high-mobility group box 1 protein

AIM

Glycyrrhizin (Gly) has been reported as an inhibitor of extracellular HMGB1 (high-mobility group box 1 protein) cytokine's activity, and protects spinal cord, liver, heart and brain against ischemia-reperfusion-induced injury in rats. The purpose of this study was to investigate the protective effect of Gly in rat skin thermal injury model and to elucidate the underlying mechanisms.

METHODS

Twenty-four male Sprague-Dawley rats (200-250g) were randomly divided into control group, vehicle-treated and Gly-treated burn groups, each group contained eight animals. In the latter two groups, rats were subjected to 30% TBSA (Total Body Surface Area) full-thickness scald injury. In Gly-treated burn group, glycyrrhizin (60mg/kg) was administered intraperitoneally immediately after and at 24th hour burn; in vehicle-treated burn group, Ringer's solution (4ml/kg, as a vehicle) was administered intraperitoneally immediately after and at 24th hour burn. The animals were sacrificed at 48h after injury. Aortic blood samples were obtained to detect tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) with ELISA (Enzyme-Linked Immuno Sorbent Assay) kits. Lung, liver and kidney tissue samples were collected to determine the expression of HMGB1 mRNA and protein. HMGB1 mRNA level was semiquantitatively measured by Real-Time PCR using β-actin as an internal standard, and protein expression of HMGBI was determined by Western blot.

RESULTS

Severe skin scald injury caused a significant increase in plasma TNF-α and IL-1β versus the control group (P<0.001) in 48h after burns. Intraperitoneal administration of Gly (60mg/kg) significantly reduced the levels of serum TNF-α and IL-1β (P<0.01). Gly treatment reduced these biochemical indices accompanied by lower level of HMGB1 protein (P<0.05) and mRNA expression (P<0.01).

CONCLUSION

These results demonstrate that Gly possesses an anti-inflammation effect to protect the remote organs from burn-induced injury.

The high-mobility group nucleosome-binding domain 5 is highly expressed in breast cancer and promotes the proliferation and invasion of breast cancer cells

The high-mobility group nucleosome-binding domain 5 (HMGN5) is a member of the high-mobility group proteins family. Previous study found that HMGN5 is required for tumorigenesis in vitro, and aberrations in the expression of HMGN5 were found in human osteosarcoma, prostate cancer, and squamous cell carcinoma. Nevertheless, the role of HMGN5 in breast cancer remains unclear. This study aimed to investigate the expression and clinical significance of HMGN5 in human breast cancer, confirm the oncogenic role of HMGN5, and explore the mechanism by which HMGN5 contributes to invasion and metastasis. HMGN5 expression was detected in breast cancer tissues and corresponding adjacent non-cancerous tissues from 43 patients by immunohistochemistry, and the clinicopathologic characteristics of all patients were also analyzed. Next, knockdown of HMGN5 protein in MDA-MB-231 cells was performed through a small interfering RNA (siRNA) technique, and cell viability, apoptosis, and invasion were detected by cell vitality test, flow cytometry, and transwell assay, respectively. Immunohistostaining showed that HMGN5 were highly expressed in the nucleus in all breast cancer tissues as compared with the adjacent non-cancerous tissues (ANCT;(73.5 ± 11 vs. 31.0 ± 5 %, P < 0.01). HMGN5 expression level was associated with the poorly differentiated tumor cells, lymph node involvement tumor, and T4 staging tumor. Knockdown of HMGN5 inhibited cell growth, suppressed invasion, and increased cell apoptosis in human breast cancer MDA-MB-231 cells. Western blot analysis demonstrated that the expressions of PCNA, connective tissue growth factor (CTGF), and MMP-9 were decreased in human breast MDA-MB-231 cells depleted of HMGN5. In addition, the apoptotic markers (cleaved PARP and cleaved caspase-3) were significantly increased by HMGN5 knockdown, but microtubule-associated protein 1 light chain 3-II/I (LC3-II/I) did not alter. HMGN5 plays an oncogenic role in human breast cancer by inhibiting cell proliferation and invasion, and activating apoptosis, which could be exploited as a target for therapy in human breast cancer.

Evolution of high mobility group nucleosome-binding proteins and its implications for vertebrate chromatin specialization

High mobility group (HMG)-N proteins are a family of small nonhistone proteins that bind to nucleosomes (N). Despite the amount of information available on their structure and function, there is an almost complete lack of information on the molecular evolutionary mechanisms leading to their exclusive differentiation. In the present work, we provide evidence suggesting that HMGN lineages constitute independent monophyletic groups derived from a common ancestor prior to the diversification of vertebrates. Based on observations of the functional diversification across vertebrate HMGN proteins and on the extensive silent nucleotide divergence, our results suggest that the long-term evolution of HMGNs occurs under strong purifying selection, resulting from the lineage-specific functional constraints of their different protein domains. Selection analyses on independent lineages suggest that their functional specialization was mediated by bursts of adaptive selection at specific evolutionary times, in a small subset of codons with functional relevance-most notably in HMGN1, and in the rapidly evolving HMGN5. This work provides useful information to our understanding of the specialization imparted on chromatin metabolism by HMGNs, especially on the evolutionary mechanisms underlying their functional differentiation in vertebrates.

Molecular cloning and characterization of high mobility group box1 (Ls-HMGB1) from humphead snapper, Lutjanus sanguineus

High mobility group box1 (HMGB1) is a kind of chromatin-associated nonhistone protein important for nucleosome formation, transcriptional regulation and inflammation. However, the reports about HMGB1 of marine fish were still limited. Here, we cloned and characterized a HMGB1 gene from humphead snapper, Lutjanus sanguineus (Ls-HMGB1). The Ls-HMGB1 cDNA composed of 1199 bp with a 70 bp of 5'-UTR, 630 bp open reading frame (ORF) and 499 bp 3'-UTR, encoded a polypeptide of 210 amino acids (GenBank Accession No: KJ783442). Sequence alignment of Ls-HMGB1 showed the highest similarity of 91% with Sciaenops ocellatus HMGB1 protein. Quantitative real-time PCR (qRT-PCR) analysis revealed that Ls-HMGB1 had relatively high expression level in skin, kidney and heart. After Vibrio harveyi and poly I:C stimulation, transcripts of Ls-HMGB1 were significantly increased and reached to peak at 18 h p.i. The L. sanguineus interleukin-6 (Ls-IL6) transcription in HK leukocytes was significantly induced by recombinant LsHMGB1 (rLsHMGB1). These results indicated that Ls-HMGB1 may play an important role in immune response of L. sanguineus during pathogen challenge.

Structural insights into the mechanism of negative regulation of single-box high mobility group proteins by the acidic tail domain

The Drosophila and plant (maize) functional counterparts of the abundant vertebrate chromosomal protein HMGB1 (HMG-D and ZmHMGB1, respectively) differ from HMGB1 in having a single HMG box, as well as basic and acidic flanking regions that vary greatly in length and charge. We show that despite these variations, HMG-D and ZmHMGB1 exist in dynamic assemblies in which the basic HMG boxes and linkers associate with their intrinsically disordered, predominantly acidic, tails in a manner analogous to that observed previously for HMGB1. The DNA-binding surfaces of the boxes and linkers are occluded in “auto-inhibited” forms of the protein, which are in equilibrium with transient, more open structures that are “binding-competent.” This strongly suggests that the mechanism of auto-inhibition may be a general one. HMG-D and ZmHMGB1 differ from HMGB1 in having phosphorylation sites in their tail and linker regions. In both cases, in vitro phosphorylation of serine residues within the acidic tail stabilizes the assembled form, suggesting another level of regulation for interaction with DNA, chromatin, and other proteins that is not possible for the uniformly acidic (hence unphosphorylatable) tail of HMGB1.

Characteristics of replication-independent endogenous double-strand breaks in Saccharomyces cerevisiae

Background

Replication-independent endogenous double-strand breaks (RIND-EDSBs) occur in both humans and yeast in the absence of inductive agents and DNA replication. In human cells, RIND-EDSBs are hypermethylated, preferentially retained in the heterochromatin and unbound by γ-H2AX. In single gene deletion yeast strains, the RIND-EDSB levels are altered; the number of RIND-EDSBs is higher in strains with deletions of histone deacetylase, endonucleases, topoisomerase, or DNA repair regulators, but lower in strains with deletions of the high-mobility group box proteins or Sir2. In summary, RIND-EDSBs are different from pathologic DSBs in terms of their causes and consequences. In this study, we identified the nucleotide sequences surrounding RIND-EDSBs and investigated the features of these sequences as well as their break locations.

Results

In recent work, we detected RIND-EDSBs using ligation mediated PCR. In this study, we sequenced RIND-EDSB PCR products of resting state Saccharomyces cerevisiae using next-generation sequencing to analyze RIND-EDSB sequences. We found that the break locations are scattered across a number of chromosomes. The number of breaks correlated with the size of the chromosomes. Most importantly, the break occurrences had sequence pattern specificity. Specifically, the majority of the breaks occurred immediately after the sequence “ACGT” (P = 2.2E-156). Because the “ACGT” sequence does not occur primarily in the yeast genome, this specificity of the “ACGT” sequence cannot be attributed to chance.

Conclusions

RIND-EDSBs occur non-randomly; that is, they are produced and retained by specific mechanisms. Because these particular mechanisms regulate their generation and they possess potentially specific functions, RIND-EDSBs could be epigenetic marks.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-750) contains supplementary material, which is available to authorized users.

High-mobility group box 1 (HMGB1) in childhood: from bench to bedside

High-mobility group box protein 1 (HMGB1) is a nonhistone nuclear protein that has a dual function. Inside the cell, HMGB1 binds DNA, regulating transcription and determining chromosomal architecture. Outside the cell, HMGB1 activates the innate system and mediates a wide range of physiological and pathological responses. HMGB1 exerts these actions through differential engagement of multiple surface receptors, including Toll-like receptor (TLR)2, TLR4, and receptor for advanced glycation end products (RAGE). HMGB1 is implicated as a late mediator of sepsis and is also involved in inflammatory and autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus. Interestingly, HMGB1 was associated with tumor progression, becoming a potential therapeutic target, due to its involvement in the resistance to chemotherapy. Its implication on the pathogenesis of systemic vasculitis and inflammatory bowel diseases has also been evaluated. Moreover, it regulates neuroinflammation after traumatic brain injuries or cerebral infectious diseases. The aim of this review is to analyze these different roles of HMGB1, both in physiological and pathological conditions, discussing clinical and scientific implications in the field of pediatrics.

CONCLUSION

HMGB1 plays a key role in several pediatric diseases, opening new scenarios for diagnostic biomarkers and therapeutic strategies development.

The ARID-HMG DNA-binding protein AtHMGB15 is required for pollen tube growth in Arabidopsis thaliana

In flowering plants, male gametes (sperm cells) develop within male gametophytes (pollen grains) and are delivered to female gametes for double fertilization by pollen tubes. Therefore, pollen tube growth is crucial for reproduction. The mechanisms that control pollen tube growth remain poorly understood. In this study, we demonstrated that the ARID-HMG DNA-binding protein AtHMGB15 plays an important role in pollen tube growth. This protein is preferentially expressed in pollen grains and pollen tubes and is localized in the vegetative nuclei of the tricellular pollen grains and pollen tubes. Knocking down AtHMGB15 expression via a Ds insertion caused retarded pollen tube growth, leading to a significant reduction in the seed set. The athmgb15-1 mutation affected the expression of 1686 genes in mature pollen, including those involved in cell wall formation and modification, cell signaling and cellular transport during pollen tube growth. In addition, it was observed that AtHMGB15 binds to DNA in vitro and interacts with the transcription factors AGL66 and AGL104, which are required for pollen maturation and pollen tube growth. These results suggest that AtHMGB15 functions in pollen tube growth through the regulation of gene expression.

High mobility group box-1 (HMGB1) participates in the pathogenesis of alcoholic liver disease (ALD)

Growing clinical and experimental evidence suggests that sterile inflammation contributes to alcoholic liver disease (ALD). High mobility group box-1 (HMGB1) is highly induced during liver injury; however, a link between this alarmin and ALD has not been established. Thus, the aim of this work was to determine whether HMGB1 contributes to the pathogenesis of ALD. Liver biopsies from patients with ALD showed a robust increase in HMGB1 expression and translocation, which correlated with disease stage, compared with healthy explants. Similar findings were observed in chronic ethanol-fed wild-type (WT) mice. Using primary cell culture, we validated the ability of hepatocytes from ethanol-fed mice to secrete a large amount of HMGB1. Secretion was time- and dose-dependent and responsive to prooxidants and antioxidants. Selective ablation of Hmgb1 in hepatocytes protected mice from alcohol-induced liver injury due to increased carnitine palmitoyltransferase-1, phosphorylated 5'AMP-activated protein kinase-α, and phosphorylated peroxisome proliferator-activated receptor-α expression along with elevated LDL plus VLDL export. Native and post-translationally modified HMGB1 were detected in humans and mice with ALD. In liver and serum from control mice and in serum from healthy volunteers, the lysine residues within the peptides containing nuclear localization signals (NLSs) 1 and 2 were non-acetylated, and all cysteine residues were reduced. However, in livers from ethanol-fed mice, in addition to all thiol/non-acetylated isoforms of HMGB1, we observed acetylated NLS1 and NLS2, a unique phosphorylation site in serine 35, and an increase in oxidation of HMGB1 to the disulfide isoform. In serum from ethanol-fed mice and from patients with ALD, there was disulfide-bonded hyperacetylated HMGB1, disulfide-bonded non-acetylated HMGB1, and HMGB1 phosphorylated in serine 35. Hepatocytes appeared to be a major source of these HMGB1 isoforms. Thus, hepatocyte HMGB1 participates in the pathogenesis of ALD and undergoes post-translational modifications (PTMs) that could condition its toxic effects.

Effector bottleneck: microbial reprogramming of parasitized host cell transcription by epigenetic remodeling of chromatin structure

Obligate intracellular pathogenic bacteria evolved to manipulate their host cells with a limited range of proteins constrained by their compact genomes. The harsh environment of a phagocytic defense cell is one that challenges the majority of commensal and pathogenic bacteria; yet, these are the obligatory vertebrate homes for important pathogenic species in the Anaplasmataceae family. Survival requires that the parasite fundamentally alter the native functions of the cell to allow its entry, intracellular replication, and transmission to a hematophagous arthropod. The small genomic repertoires encode several eukaryotic-like proteins, including ankyrin A (AnkA) of Anaplasma phagocytophilum and Ank200 and tandem-repeat containing proteins of Ehrlichia chaffeensis that localize to the host cell nucleus and directly bind DNA. As a model, A. phagocytophilum AnkA appears to directly alter host cell gene expression by recruiting chromatin modifying enzymes such as histone deacetylases and methyltransferases or by acting directly on transcription in cis. While cis binding could feasibly alter limited ranges of genes and cellular functions, the complex and dramatic alterations in transcription observed with infection are difficult to explain on the basis of individually targeted genes. We hypothesize that nucleomodulins can act broadly, even genome-wide, to affect entire chromosomal neighborhoods and topologically associating chromatin domains by recruiting chromatin remodeling complexes or by altering the folding patterns of chromatin that bring distant regulatory regions together to coordinate control of transcriptional reprogramming. This review focuses on the A. phagocytophilum nucleomodulin AnkA, how it impacts host cell transcriptional responses, and current investigations that seek to determine how these multifunctional eukaryotic-like proteins facilitate epigenetic alterations and cellular reprogramming at the chromosomal level.

HMGN2, a new anti-tumor effector molecule of CD8⁺ T cells

Background

Cytolytic T lymphocytes (CTL) and natural killer (NK) cells have been implicated as important cells in antitumor responses. Our previous research has shown that high mobility group nucleosomal-binding domain 2 (HMGN2) could be released by IL-2 and PHA stimulated peripheral blood mononuclear cells (PBMCs) and also induced tumor cells apoptosis at low doses. In this study, we isolated and cultured PBMCs and CD8⁺ T cells to analyze the expression and antitumor effects of HMGN2.

Methods

PBMCs from healthy donors were isolated using Human Lymphocyte Separation tube. CD8⁺ T cells were separated from the PBMCs using MoFlo XDP high-speed flow cytometry sorter. Activation of PBMCs and CD8⁺ T cells were achieved by stimulating with Phytohemagglutinin (PHA) or tumor antigen. In addition, the methods of ELISA, intracellular staining, and fluorescence-labeling assays were used.

Results

PHA induced PBMCs to release high levels of HMGN2, and CD8⁺ T cells was the major cell population in PBMCs that release HMGN2 after PHA activation. Tumor antigen-activated CD8⁺ T cells also released high levels of HMGN2. Supernatants of tumor antigen-activated CD8⁺ T cells were able to kill tumor cells in a dose-dependent manner. This antitumor effect could be significantly blocked by using an anti-HMGN2 antibody. Fluorescence-labeling assays showed that the supernatant proteins of activated CD8⁺ T cells could be transported into tumor cells, and the transport visibly decreased after HMGN2 was depleted by anti-HMGN2 antibody.

Conclusions

These results suggest that HMGN2 is an anti-tumor effector molecule of CD8⁺ T cells.

Generation and characterisation of a canine EGFP-HMGA2 prostate cancer in vitro model

The architectural transcription factor HMGA2 is abundantly expressed during embryonic development. In several malignant neoplasias including prostate cancer, high re-expression of HMGA2 is correlated with malignancy and poor prognosis. The let-7 miRNA family is described to regulate HMGA2 negatively. The balance of let-7 and HMGA2 is discussed to play a major role in tumour aetiology. To further analyse the role of HMGA2 in prostate cancer a stable and highly reproducible in vitro model system is precondition. Herein we established a canine CT1258-EGFP-HMGA2 prostate cancer cell line stably overexpressing HMGA2 linked to EGFP and in addition the reference cell line CT1258-EGFP expressing solely EGFP to exclude EGFP-induced effects. Both recombinant cell lines were characterised by fluorescence microscopy, flow cytometry and immunocytochemistry. The proliferative effect of ectopically overexpressed HMGA2 was determined via BrdU assays. Comparative karyotyping of the derived and the initial CT1258 cell lines was performed to analyse chromosome consistency. The impact of the ectopic HMGA2 expression on its regulator let-7a was analysed by quantitative real-time PCR. Fluorescence microscopy and immunocytochemistry detected successful expression of the EGFP-HMGA2 fusion protein exclusively accumulating in the nucleus. Gene expression analyses confirmed HMGA2 overexpression in CT1258-EGFP-HMGA2 in comparison to CT1258-EGFP and native cells. Significantly higher let-7a expression levels were found in CT1258-EGFP-HMGA2 and CT1258-EGFP. The BrdU assays detected an increased proliferation of CT1258-HMGA2-EGFP cells compared to CT1258-EGFP and native CT1258. The cytogenetic analyses of CT1258-EGFP and CT1258-EGFP-HMGA2 resulted in a comparable hyperdiploid karyotype as described for native CT1258 cells. To further investigate the impact of recombinant overexpressed HMGA2 on CT1258 cells, other selected targets described to underlie HMGA2 regulation were screened in addition. The new fluorescent CT1258-EGFP-HMGA2 cell line is a stable tool enabling in vitro and in vivo analyses of the HMGA2-mediated effects on cells and the development and pathogenesis of prostate cancer.

Protective effects of hesperidin on concanavalin A-induced hepatic injury in mice

Hesperidin (HDN) is a citrus bioflavonoid, which widely exists in many plants. Previous researches have proved that HDN has several functions such as anti-oxidant, anti-tumor, anti-inflammatory, immune regulation and so on. In the present study, we explored the protective effects of HDN on concanavalin A (Con A)-induced hepatic injury. Acute hepatic injury model was established successfully by intravenous administration of Con A (15 mg/kg) in male C57BL/6 mice, and HDN was pretreated for 10 days before Con A challenge. It was found that the hepatic injury was notably improved in HDN pretreated mice. Furthermore, hepatic oxidative stress and the production of proinflammatory cytokines including TNF-α and IFN-γ were decreased by HDN pretreatment. More importantly, compared with Con A-treated mice, the expression and releasing of HMGB1 and T-cell activation were markedly reduced in HDN pretreated mice. Thus, these results suggest that HDN protects mice from Con A-induced hepatic injury by suppressing hepatocyte oxidative stress, producing cytokines, expressing and releasing HMGB1 and activating T cells.

HuR and miR-1192 regulate myogenesis by modulating the translation of HMGB1 mRNA

Upon muscle injury, the high mobility group box 1 (HMGB1) protein is upregulated and secreted to initiate reparative responses. Here we show that HMGB1 controls myogenesis both in vitro and in vivo during development and after adult muscle injury. HMGB1 expression in muscle cells is regulated at the translational level: the miRNA miR-1192 inhibits HMGB1 translation and the RNA-binding protein HuR promotes it. HuR binds to a cis-element, HuR binding sites (HuRBS), located in the 3'UTR of the HMGB1 transcript, and at the same time miR-1192 is recruited to an adjacent seed element. The binding of HuR to the HuRBS prevents the recruitment of Argonaute 2 (Ago2), overriding miR-1192-mediated translation inhibition. Depleting HuR reduces myoblast fusion and silencing miR-1192 re-establishes the fusion potential of HuR-depleted cells. We propose that HuR promotes the commitment of myoblasts to myogenesis by enhancing the translation of HMGB1 and suppressing the translation inhibition mediated by miR-1192.

Apoptotic response through a high mobility box 1 protein-dependent mechanism in LPS/GalN-induced mouse liver failure and glycyrrhizin-mediated inhibition

HMGB1 is a nuclear component involved in nucleosome stabilization and transcription regulation, but extracellularly it is able to serve as a potential late mediator of lethality. In the present study, we explored inflammation-promoting activity of HMGB1 and blockade of extracellular release of HMGB1 by glycyrrhizin (GL) in LPS/GalN-triggered mouse liver injury. At 1 to 10 h after LPS/GalN-treatment, mice were anesthetized to collect blood from heart puncture, and serum transaminase and HMGB1 were evaluated. Administration of LPS/GalN precipitated tissue injury associated with time-dependent alteration in HMGB1 serum levels. At 8 h nuclear immunoreactive products were remarkably reduced and extracellular HMGB1 expression was found exclusively in the pericentral foci. The treatment with GL significantly down-regulated the serum levels of ALT, AST, and HMGB1 in addition to the strong inhibition of tissue injury and extracellular immunoreactivity to HMGB1 and to acetylated-lysine. Furthermore, GL brought about a significant decrease in the number of apoptotic hepatocytes labeled with TUNEL-method. On the basis of these results, three apoptosis-associated genes were identified with microarray analysis and real-time PCR. The ChIP-assay revealed the binding of HMGB1 protein to Gsto1 promoter sequence in LPS/GalN-treated mice and the remarkable decrease in combined HMGB1 protein by GL. The current findings claim that a single injection of LPS/GalN might stimulate apoptosis of hepatocytes through the binding of HMGB1 protein to Gsto1 promoter region and that GL-treatment might prevent the apoptosis and inflammatory infiltrates caused with LPS/GalN-injection by disturbing the binding of HMGB1 protein to Gsto1 promoter sequence.

Cloning and expression analysis of a novel high-mobility group box 2 homologue from Lampetra japonica

High-mobility group box 2 (HMGB2) is a nonhistone architectural protein that plays important roles in many biological processes. In this study, we cloned a homologue of the HMGB2 from the lymphocyte-like cells of Lampetra japonica (L. japonica). Sequence analysis reveals that L. japonica HMGB2 contains two highly conserved motifs and shares more than 70 % identity with the homologues from other vertebrate species. Subsequently, Lj-HMGB2 was subcloned into the pET-28a(+) and pIRES2 AcGFP1-Nuc vector and expressed in Rosetta blue (DE3) and Hela cell lines, respectively. The recombinant L. japonica HMGB2 (rLj-HMGB2) with apparent molecular mass of 22 kDa was further purified by His-Bind affinity chromatography. Real-time quantitative PCR indicates that the expression level of Lj-HMGB2 was particularly up-regulated in intestines after challenged with lipopolysaccharide, while up-regulated in lymphocyte-like cells and heart after challenged with concanavalin A in vivo. In addition, rLj-HMGB2 could induce the generation of proinflammatory mediators in the activated human acute monocytic leukemia cell line (THP1), which suggested that Lj-HMGB2 may participate in the immune response of the lampreys.

High-mobility group nucleosome-binding domain 5 increases drug resistance in osteosarcoma through upregulating autophagy

Although tumor therapy has been improved in the past decades, the survival outcomes for osteosarcoma remain unsatisfactory, and one of the primary reasons for the failure of current treatment is that patients with late-stage cancer often develop resistance to anticancer drugs. High-mobility group nucleosome-binding domain 5 (HMGN5) is a newly identified gene associated with cancer and autophagy, which could inhibit apoptosis induced by anticancer agents. However, it is still unclear whether HMGN5 regulated autophagy in osteosarcoma, and the mechanism and significance of HMGN5-mediated autophagy in tumor therapy is never investigated. In this study, we first detected HMGN5 in vivo and in vitro. HMGN5 was highly expressed in osteosarcoma tumor, especially in posttreatment tumor. Next, we employed adenovirus-mediated overexpression of HMGN5 in U-2OS and MG63 to investigate the role of HMGN5 in osteosarcoma cell lines. Adenovirus-mediated overexpression of HMGN5 could efficiently upregulate the expression level of HMGN5 in osteosarcoma cell lines at both messenger RNA (mRNA) and protein levels. Anticancer agents namely doxorubicin, cisplatin, and methotrexate each induced HMGN5 upregulation in human U-2OS and MG63 osteosarcoma cell lines. In addition, overexpression of HMGN5 reduced the chemosensitivity of osteosarcoma cells in vitro, and the mechanistic investigation revealed that HMGN5 increased drug resistance by upregulating autophagy. Therefore, HMGN5 is a critical factor in the development of chemoresistance through regulating autophagy, and it offers a novel target for improving osteosarcoma therapy.

A dual-role of Gu-4 in suppressing HMGB1 secretion and blocking HMGB1 pro-inflammatory activity during inflammation

Background

High mobility group box 1(HMGB1) was first recognized as a nuclear protein that increased the chromatin remodeling and regulates transcription of many genes. In recent years, HMGB1 has been identified as a critical “late” pro-inflammatory mediator due to its unique secretion pattern and lethal effects in sepsis. Therefore, preventing the active release and inhibiting the pro-inflammatory activity of HMGB1 become promising strategies for the treatment of sepsis. Here, we reported the therapeutic effects of Gu-4, a lactosyl derivative, on sepsis and the underlying molecular mechanisms.

Methodology/Principal Findings

In an experimental rat model of sepsis caused by cecal ligation and puncture (CLP), Gu-4 administration prominently attenuated lung injury and improved the survival of the septic animals, which was positively correlated with the decrease of the serum HMGB1 level. Using RAW264.7 macrophage cell line, we further showed that Gu-4 significantly suppressed the lipopolysaccharide (LPS)-induced release and cytoplasmic translocation of HMGB1. Moreover, Gu-4 not only dose-dependently attenuated recombinant human (rhHMGB1)-induced production of TNF-α, IL-6, and IL-1β in THP-1 cells, but also greatly inhibited the adhesion of rhHMGB1-challenged THP-1 cells to HUVECs. Analyses of flow cytometry demonstrated that Gu-4 could effectively reduce the activation of CD11b elicited by rhHMGB1. Western blot analyses revealed that Gu-4 treatment could partially block the rhHMGB1-induced activation of ERK and NF-κB signalings. Meanwhile, CD11b knockdown also obviously attenuated the rhHMGB1-induced phosphorylations of ERK and IKKα/β.

Conclusions/Significance

Taken together, our results suggest that Gu-4 possesses a therapeutic potential in the treatment of sepsis probably via inhibiting the LPS-induced release of HMGB1 from macrophages and via suppressing the pro-inflammatory activity of HMGB1.

Protective effect of glycyrrhizin, a direct HMGB1 inhibitor, on focal cerebral ischemia/reperfusion-induced inflammation, oxidative stress, and apoptosis in rats

Aim

Glycyrrhizin (GL) has been reported to protect against ischemia and reperfusion (I/R)-induced injury by inhibiting the cytokine activity of high mobility group box 1 (HMGB1). In the present study, the protective effects of GL against I/R injury, as well as the related molecular mechanisms, were investigated in rat brains.

Methods

Focal cerebral I/R injury was induced by intraluminal filamentous occlusion of the middle cerebral artery (MCA) in Male Sprague-Dawley rats. GL alone or GL and rHMGB1 were administered intravenously at the time of reperfusion. Serum levels of HMGB1 and inflammatory mediators were quantified via enzyme-linked immunosorbent assay (ELISA). Histopathological examination, immunofluorescence, RT-PCR and western blotting analyses were performed to investigate the protective and anti-apoptotic effects and related molecular mechanisms of GL against I/R injury in rat brains.

Results

Pre-treatment with GL significantly reduced infarct volume and improved the accompanying neurological deficits in locomotor function. The release of HMGB1 from the cerebral cortex into the serum was inhibited by GL administration. Moreover, pre-treatment with GL alleviated apoptotic injury resulting from cerebral I/R through the inhibition of cytochrome C release and caspase 3 activity. The expression levels of inflammation- and oxidative stress-related molecules including TNF-α, iNOS, IL-1β, and IL-6, which were over-expressed in I/R, were decreased by GL. P38 and P-JNK signalling were involved in this process. All of the protective effects of GL could be reversed by rHMGB1 administration.

Conclusions

GL has a protective effect on ischemia-reperfusion injury in rat brains through the inhibition of inflammation, oxidative stress and apoptotic injury by antagonising the cytokine activity of HMGB1.

Inhibition of extracellular HMGB1 attenuates hyperoxia-induced inflammatory acute lung injury

Prolonged exposure to hyperoxia results in acute lung injury (ALI), accompanied by a significant elevation in the levels of proinflammatory cytokines and leukocyte infiltration in the lungs. However, the mechanisms underlying hyperoxia-induced proinflammatory ALI remain to be elucidated. In this study, we investigated the role of the proinflammatory cytokine high mobility group box protein 1 (HMGB1) in hyperoxic inflammatory lung injury, using an adult mouse model. The exposure of C57BL/6 mice to ≥99% O₂ (hyperoxia) significantly increased the accumulation of HMGB1 in the bronchoalveolar lavage fluids (BALF) prior to the onset of severe inflammatory lung injury. In the airways of hyperoxic mice, HMGB1 was hyperacetylated and existed in various redox forms. Intratracheal administration of recombinant HMGB1 (rHMGB1) caused a significant increase in leukocyte infiltration into the lungs compared to animal treated with a non-specific peptide. Neutralizing anti-HMGB1 antibodies, administrated before hyperoxia significantly attenuated pulmonary edema and inflammatory responses, as indicated by decreased total protein content, wet/dry weight ratio, and numbers of leukocytes in the airways. This protection was also observed when HMGB1 inhibitors were administered after the onset of the hyperoxic exposure. The aliphatic antioxidant, ethyl pyruvate (EP), inhibited HMGB1 secretion from hyperoxic macrophages and attenuated hyperoxic lung injury. Overall, our data suggest that HMGB1 plays a critical role in mediating hyperoxic ALI through the recruitment of leukocytes into the lungs. If these results can be translated to humans, they suggest that HMGB1 inhibitors provide treatment regimens for oxidative inflammatory lung injury in patients receiving hyperoxia through mechanical ventilation.

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Exposure to hyperoxia results in accumulation of high levels of airway HMGB1 that precede inflammatory acute lung injury (ALI).

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Airway HMGB1 is critical in mediating hyperoxia-induced inflammatory ALI via recruiting leukocytes including neutrophils.

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Extracellular HMGB1-accumulated upon prolonged exposure to hyperoxia is hyperacetylated, existing in different redox states.

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Small molecule EP, administrated even after the onset of hyperoxic exposure, can mitigate hyperoxia-induced inflammatory ALI by inhibiting HMGB1 release into the extracellular milieu.

Aberrant neural stem cell proliferation and increased adult neurogenesis in mice lacking chromatin protein HMGB2

Neural stem and progenitor cells (NSCs/NPCs) are distinct groups of cells found in the mammalian central nervous system (CNS). Previously we determined that members of the High Mobility Group (HMG) B family of chromatin structural proteins modulate NSC proliferation and self-renewal. Among them HMGB2 was found to be dynamically expressed in proliferating and differentiating NSCs, suggesting that it may regulate NSC maintenance. We report now that Hmgb2(-/-) mice exhibit SVZ hyperproliferation, increased numbers of SVZ NSCs, and a trend towards aberrant increases in newly born neurons in the olfactory bulb (OB) granule cell layer. Increases in the levels of the transcription factor p21 and the Neural cell adhesion molecule (NCAM), along with down-regulation of the transcription/pluripotency factor Oct4 in the Hmgb2-/- SVZ point to a possible pathway for this increased proliferation/differentiation. Our findings suggest that HMGB2 functions as a modulator of neurogenesis in young adult mice through regulation of NSC proliferation, and identify a potential target via which CNS repair could be amplified following trauma or disease-based neuronal degeneration.

Thrombomodulin's lectin-like domain reduces myocardial damage by interfering with HMGB1-mediated TLR2 signalling

AIMS

Thrombomodulin (TM), via its lectin-like domain (LLD), exhibits anti-inflammatory properties partly by sequestering the pro-inflammatory cytokine, high-mobility group box 1 (HMGB1). Since myocardial damage after ischaemia and reperfusion is mediated by inflammation, we evaluated the cardioprotective effects of the LLD of TM. Using an in vivo mouse model of transient ischaemia and in vitro models of cardiomyocyte hypoxia, we assessed the ability of the LLD to suppress HMGB1-mediated activation of the receptors, receptor for advanced glycation endproducts (RAGEs) and Toll-like receptors (TLRs) 2 and 4.

METHODS AND RESULTS

Thirty-minute myocardial ischaemia was induced in isoflurane-anaesthetized mice followed by 24 h of reperfusion in wild-type (WT) mice, in mice lacking the LLD of TM (TM(LeD/LeD) mice), and in WT with systemic overexpression of the LLD of TM induced by hydrodynamic transfection. Infarct size, HMGB1 protein, and apoptotic cells were significantly increased in TM(LeD/LeD) mice when compared with WT. Neonatal rat cardiomyocytes transfected with TLR2-, TLR4-, and RAGE-siRNA were exposed to hypoxia (0.8% O2) and reoxygenation (21% O2). HMGB1 augmented hypoxia-induced apoptosis in TLR2- but not in RAGE- or TLR4-suppressed cells. Administration of HMGB1- and TLR2-blocking antibodies in TM(LeD/LeD) mice prior to myocardial ischaemia diminished apoptosis. Therapeutic systemic gene therapy using the LLD reduced the infarct size and HMGB1 protein levels 24 h after reperfusion.

CONCLUSION

The LLD of TM suppresses HMGB1-induced and TLR2-mediated myocardial reperfusion injury and apoptosis in vitro and in vivo.