HMGB1 inhibits cell death in yeast and mammalian cells and is abundantly expressed in human breast carcinoma

The association of HMGB1 expression with clinicopathological significance and prognosis in hepatocellular carcinoma: a meta-analysis and literature review

Background

Hepatocellular carcinoma (HCC) is the fifth most common cancer, and it is the second most common cancer-related mortality globally. The prognostic value of high mobility group box 1 (HMGB1) remains controversial. The purpose of this study is to conduct a meta-analysis and literature review to evaluate the association of HMGB1 expression with the prognosis of patients with HCC.

Methods

A detailed literature search was made in Medline, Google Scholar and others for related research publications. The data were extracted and assessed by two reviewers independently. Analysis of pooled data were performed, Hazard Ratio (HR) and mean difference with corresponding confidence intervals (CIs) were calculated and summarized respectively.

Results

10 relevant articles were included for this meta-analysis study. HMGB1 mRNA levels in HCC were significantly higher than those in normal (p<0.00001) and para-tumor tissues (p = 0.002) respectively. The protein levels of HMGB1 in HCC were significantly higher than those in para-tumor tissues (p = 0.005). Two studies reported the serum HMGB1 levels in patients with HCC of TNM stages, and indicating significantly different between stage I and II, stage II and III, as well as stage III and IV (two studies showed p<0.01 and p<0.001 respectively). The overall survival (OS) was significantly shorter in HCC patients with high HMGB1 expression compared those with low HMGB1 expression and the pooled HR was 1.31 with 95% CI 1.20–1.44, Z = 5.82, p<0.0001. Two additional studies showed that there were higher serum HMGB1 levels in patients with chronic hepatitis than those in healthy people (p<0.05).

Conclusions

The results of this meta-analysis suggest that HMGB1 mRNA and protein tissue levels in the patients with HCC are significantly higher than those in para-tumor and normal liver tissues respectively. Tissue HMGB1 overexpression is a potential biomarker for HCC diagnosis, and it is significantly associated with the prognosis of patients with HCC.

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.

The role of high mobility group box 1 in innate immunity

With growing accounts of inflammatory diseases such as sepsis, greater understanding the immune system and the mechanisms of cellular immunity have become primary objectives in immunology studies. High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is implicated in various aspects of the innate immune system as a damage-associated molecular pattern molecule and a late mediator of inflammation, as well as in principal cellular processes, such as autophagy and apoptosis. HMGB1 functions in the nucleus as a DNA chaperone; however, it exhibits cytokine-like activity when secreted by injurious or infectious stimuli. Extracellular HMGB1 acts through specific receptors to promote activation of the NF-κB signaling pathway, leading to production of cytokines and chemokines. These findings further implicate HMGB1 in lethal inflammatory diseases as a crucial regulator of inflammatory, injurious, and infectious responses. In this paper, we summarize the role of HMGB1 in inflammatory and non-inflammatory states and assess potential therapeutic approaches targeting HMGB1 in inflammatory diseases.

High mobility group box 1 (HMGB1) phenotypic role revealed with stress

High mobility group box 1 (HMGB1) is an evolutionarily ancient protein that is present in one form or another in all eukaryotes. It fundamentally resides in the nucleus but translocates to the cytosol with stress and is subsequently released into the extracellular space. HMGB1 global knockout mice exhibit lethal hypoglycemia, whereas tissues and cells from conditional knockout or knock-in mice are born alive without apparent significant functional deficit. An aberrant response to targeted stress in the liver, pancreas, heart or myeloid cells is consistent with a protective role for HMGB1 in sustaining nuclear homeostasis and enabling other stress responses, including autophagy. Under some conditions, HMGB1 is not required for liver and heart function. Many challenges remain with respect to understanding the multiple roles of HMGB1 in health and disease.

Overexpression of HMGB1 in melanoma predicts patient survival and suppression of HMGB1 induces cell cycle arrest and senescence in association with p21 (Waf1/Cip1) up-regulation via a p53-independent, Sp1-dependent pathway

Although laboratory studies have implicated the high mobility group box 1 (HMGB1) in melanoma, its clinical relevance remains unclear. We analyzed nearly 100 cases of human melanoma and found that HMGB1 was highly overexpressed in melanoma samples relative to normal skin and nevi tissues. Significantly, higher levels of HMGB1 correlated with more advanced disease stages and with poorer survival in melanoma patients. Unlike the well-documented pro-inflammatory role of the extracellular HMGB1, we found that its intracellular activity is necessary for melanoma cell proliferation. An absolute dependency of melanoma cell proliferation on HMGB1 was underscored by the marked response of cell cycle arrest and senescence to HMGB1 knockdown. We demonstrated that HMGB1 deficiency-induced inhibition of cell proliferation was mediated by p21, which was induced via a Sp1-dependent mechanism. Taken together, our data demonstrate a novel oncogenic role of HMGB1 in promoting human melanoma cell proliferation and have important implications in melanoma patient care.

HMGB1-mediated autophagy promotes docetaxel resistance in human lung adenocarcinoma

Background

Docetaxel resistance remains a major obstacle in the treatment of non-small cell lung cancer (NSCLC). High-mobility group box 1 (HMGB1) has been shown to promote autophagy protection in response to antitumor therapy, but the exact molecular mechanism underlying HMGB1-mediated autophagy has not been clearly defined.

Methods

Lung adenocarcinoma (LAD) cells were transfected with pcDNA3.1-HMGB1 or HMGB1 shRNA, followed by docetaxel treatment. Cell viability and proliferation were tested by MTT assay and colony formation assay, respectively. Annexin V flow cytometric analysis and western blot analysis of activated caspase3 and cleaved PARP were used to evaluate apoptosis, while immunofluorescence microscopy and transmission electron microscopy were applied to assess autophagy activity. The formation of the Beclin-1-PI3K-III complex was examined by immunoprecipitation analysis. NOD/SCID mice were inoculated with docetaxel-resistant SPC-A1/DTX cells transfected with control or HMGB1 shRNA.

Results

HMGB1 translocated from the nucleus to the cytoplasm in LAD cells exposed to docetaxel and acted as a positive regulator of autophagy, which inhibited apoptosis and increased drug resistance. Suppression of HMGB1 restored the sensitivity of LAD cells to docetaxel both in vivo and in vitro. Mechanistic investigation revealed that HMGB1 promoted the formation of the Beclin-1-PI3K-III complex through activating the mitogen-activated protein kinase (MEK)-extracellular signal-regulated kinase (ERK) signaling pathway, thereby regulating autophagosome formation.

Conclusions

Our results demonstrated that HMGB1-regulated autophagy is a significant contributor to docetaxel resistance in LAD cells. Suppression of HMGB1 or limiting HMGB1 cytosolic translocation diminished autophagic protection in response to docetaxel in LAD cells.

Expression and effects of high-mobility group box 1 in cervical cancer

We investigated the significance of high- mobility group box1 (HMGB1) and T-cell-mediated immunity and prognostic value in cervical cancer. HMGB1, forkhead/winged helix transcription factor p3 (Foxp3), IL-2, and IL-10 protein expression was analyzed in 100 cervical tissue samples including cervical cancer, cervical intraepithelial neoplasia (CIN), and healthy control samples using immunohistochemistry. Serum squamous cell carcinoma antigen (SCC-Ag) was immunoradiometrically measured in 32 serum samples from 37 cases of squamous cervical cancer. HMGB1 and SCC-Ag were then correlated to clinicopathological characteristics. HMGB1 expression tends to increase as cervical cancer progresses and it was found to be significantly correlated to FIGO stage and lymph node metastasis. These findings suggest that HMGB1 may be a useful prognostic indicator of cervical carcinoma. In addition, there were significant positive relationships between HMGB1 and FOXP3 or IL-10 expression (both p < 0.05). In contrast, HMGB1 and IL-2 expression was negatively correlated (p < 0.05). HMGB1 expression may activate Tregs or facilitate Th2 polarization to promote immune evasion of cervical cancer. Elevated HMGB1 protein in cervical carcinoma samples was associated with a high recurrence of HPV infection in univariate analysis (p < 0.05). HMGB1 expression and levels of SCC-Ag were directly correlated in SCC (p < 0.05). Thus, HMGB1 may be a useful biomarker for patient prognosis and cervical cancer prediction and treatment.

HMGB1 in hormone-related cancer: a potential therapeutic target

High-mobility group box 1 (HMGB1) is a dynamic nuclear protein participating in transcription, chromatin remodelling, and DNA recombination and repair processes. Accumulating evidence indicates that its function now extends beyond the nucleus, notably its extracellular role in inflammation. HMGB1 is implicated as a late mediator of sepsis and is also believed to promote atherosclerosis and other inflammatory diseases such as rheumatoid arthritis and systemic lupus erythematosus. Interestingly, deregulation of HMGB1 is shown to be associated with the hallmarks of cancer development. Moreover, several clinical studies have shown that HMGB1 is a promising biomarker for a variety of cancer types. In this review, we provide novel insights into the role and mechanisms of HMGB1, in particular, to hormone-related cancers and its potential to serve as a therapeutic target.

miR-200c inhibits metastasis of breast cancer cells by targeting HMGB1

miR-200c has been shown to regulate the epithelial-mesenchymal transition (EMT) by inhibiting ZEB1 and ZEB2 expression in breast cancer cells. This study further examined the role of miR-200c in the invasion and metastasis of breast cancer that goes beyond the regulation on ZEB1 and ZEB2 expression. In this study, the bioinformatics software (miRanda) was used to predict the target gene of miR-200c and Renilla luciferase assay to verify the result. The metastatic breast cancer cells MDA-MB-231 were cultured and transfected with the miR-200c mimic or inhibitor. The expressions of miR-200c and HMGB1 were detected by RT-PCR and Western blotting, respectively. Transwell assay and wound healing assay were employed to examine the invasive and migrating ability of transfected cells. Target prediction and Renilla luciferase analysis revealed that HMGB1 was a putative target gene of miR-200c. After transfection of MDA-MB-231 cells with the miR-200c mimic or inhibitor, the expression of miR-200c was significantly increased or decreased when compared with cells transfected with the miR-200c mimic NC or inhibitor NC. Moreover, the expression of HMGB1 was reversely correlated with that of miR-200c in transfected cells. Tranwell assay showed that the number of invasive cells was significantly reduced in miR-200c mimic group when compared with miR-200c inhibitor group. It was also found that the migrating ability of cells transfected with miR-200c mimics was much lower than that of cells transfected with miR-200c inhibitors. It was suggested that miR-200c can suppress the invasion and migration of breast cancer cells by regulating the expression of HMGB1. miR-200c and HMGB1 may become useful biomarkers for progression of breast cancer and targets of gene therapy.

The role of high mobility group box 1 (HMGB1) in colorectal cancer

Background

HMGB1, the most important member of the high mobility group box protein family, is a nuclear protein with different functions in the cell; it has a role in cancer progression, angiogenesis, invasion, and metastasis development. We studied the expression of HMGB1 and whether it is a prognostic factor in colorectal carcinoma.

Material/Methods

The study included 110 cases that were histopathologically diagnosed with colorectal carcinoma from the tissue samples acquired by surgical resection and biopsy in Antalya Education and Research Hospital between 2008 and 2012. HMGB1 expression was examined via immunohistochemical method.

Results

HMGB1 expression was evaluated as negative in 32 (44.4%) of the patients and as positive in 40 (55.6%) patients. There was no relation between the HMGB1 expression and sex, age, tumor invasion depth, and histological type. However, a significant relation was detected between the HMGB1 expression and lymph node status, metastasis status, and stage (p:<0.001, p:<0.001, p:<0.001, respectively). Similar results were obtained for the relations between the HMGB1 and histological grade, perineural invasion, lymphovascular invasion, and lymphocytic response (p<0.001, p<0.001, p<0.001, and p<0.001, respectively).

Conclusions

The results of our study demonstrate that HMGB1 overexpression has a significant role in tumor progression (especially migration of tumor cells) and tumor ability to metastasize in colorectal cancers; thus, it corroborates the idea that it might be an important prognostic factor.

The association of HMGB1 gene with the prognosis of HCC

High-mobility group box 1 protein (HMGB1) is an evolutionarily ancient and critical regulator of cell death and survival. HMGB1 is a chromatin-associated nuclear protein molecule that triggers extracellular damage. The expression of HMGB1 has been reported in many types of cancers, but the role of HMGB1 in hepato cellular carcinoma (HCC) is unknown.The aim of this study was to analyze the roles of HMGB1 in HCC progression using HCC clinical samples. We also investigated the clinical outcomes of HCC samples with a special focus on HMBG1 expression. In an immunohistochemical study conducted on 208 cases of HCC, HMGB1 had high expression in 134 cases(64.4%).The HMGB1 expression level did not correlate with any clinicopathological parameters, except alpha fetoprotein (AFP) (p = 0.041) and CLIP stage (p = 0.007). However, survival analysis showed that the group with HMBG1 overexpression had a significantly shorter overall survival time than the group with a down-regulatedexpression of HMBG1 (HR = 0.568, CI (0.398, 0.811), p = 0.002). Multivariate analysis showed that HMGB1 expression was a significant and independent prognostic parameter (HR = 0.562, CI (0.388, 0.815), p = 0.002) for HCC patients. The ability of proliferation, migration and invasion of HCC cells was suppressed with the disruption of endogenous HMGB1 using small interfering RNAs. On the other hand, the ability of proliferation, migration and invasion of HCC cells was strengthened when the expression endogenous HMGB1 was enhanced using HMGB1 DNA. HMGB1 expression may be a novel and independent predictor for the prognosis of HCC patients. The overexpression of HMGB1 in HCC could be a novel, effective, and supplementary biomarker for HCC, since it plays a vital role in the progression of HCC.

MiRNA-218, a new regulator of HMGB1, suppresses cell migration and invasion in non-small cell lung cancer

MicroRNAs (miRNAs) function as negative regulators of gene expression involved in cancer metastasis. The aim of this study is to investigate the potential roles of miR-218 in non-small cell lung cancer and validate its regulation mechanism. Functional studies showed that miR-218 overexpression inhibited cell migration and invasion, but had no effect on cell viability. Enhanced green fluorescent protein reporter assay, real-time polymerase chain reaction and western blot analysis confirmed that miR-218 suppressed the expression of high mobility group box-1 (HMGB1) by directly targeting its 3'-untranslated region. Accordingly, silencing of HMGB1 accorded with the effects of miR-218 on cell migration and invasion, and overexpression of HMGB1 can restore cell migration and invasion which were reduced by miR-218. In conclusion, these findings demonstrate that miR-218 functions as a tumor suppressor in lung cancer. Furthermore, miR-218 may act as a potential therapeutic biomarker for metastatic lung cancer patients.

High mobility group box 1 promotes tumor cell migration through epigenetic silencing of semaphorin 3A

High mobility group box 1 (HMGB1) is a 25-kDa chromatin-associated protein that aids in transcription and DNA repair by directly binding to DNA and altering its conformation. Additionally, HMGB1 can act as an extracellular ligand. When released from dying or stressed cells, HMGB1 binds to the RAGE receptor and activates the p42/44 MAP kinase (MAPK) cascade. HMGB1 is overexpressed in many types of cancer and frequently associated with tumor stage and metastasis. This has predominantly been attributed to an autocrine function that drives MAPK pathway activity. However, by using tumor cells with activating MAPK pathway mutations, we have identified a role for HMGB1 in promoting metastasis and tumor growth that is independent of this pathway. In the absence of HMGB1, these tumor cells show defective in vitro migration as well as reduced metastasis and tumor growth in vivo despite high p42/44 phosphorylation. We found that semaphorin 3A (SEMA3A), previously shown to act as a suppressor of angiogenesis and migration, was highly increased during expression in the absence of HMGB1. SEMA3A/HMGB1 double knockdown rescued the migration defect in HMGB1 single knockdown cells. HMGB1 bound at the semaphorin 3A genomic locus, promoted hetrochromatin formation, and decreased occupancy of acetylated histones. Based on human tumor gene expression databases, HMGB1 was significantly inversely correlated with SEMA3A, suggesting that this mechanism may be more widely relevant in different cancer types.

Should a Toll-like receptor 4 (TLR-4) agonist or antagonist be designed to treat cancer? TLR-4: its expression and effects in the ten most common cancers

Toll-like receptor 4 (TLR-4) is well known for its host innate immunity. Despite the fact that TLR-4 activation confers antitumor responses; emerging evidence suggests that TLR-4 is associated with tumor development and progression. It is now clear that overactivation of TLR-4, through various immune mediators, may cause immune response dysfunction, resulting in tumorigenesis. Different cancers could have different extents of TLR-4 involvement during tumorigenesis or tumor progression. In this review, we focus on infection- and inflammation-related TLR-4 activation in noncancer and cancer cells, as well as on the current evidence about the role of TLR-4 in ten of the most common cancers, viz, head and neck cancer, lung cancer, gastrointestinal cancer, liver cancer, pancreatic cancer, skin cancer, breast cancer, ovarian cancer, cervical cancer, and prostate cancer.

Serum HMGB1 as a diagnostic marker for malignant peritoneal mesothelioma

BACKGROUND

Diffuse malignant peritoneal mesothelioma (DMPM) is an aggressive malignant tumor of mesothelial origin that shows a limited response to cytoreductive surgery along with intraperitoneal chemotherapy. Therefore, early diagnosis of DMPM is very important. Some researchers have previously reported that high-mobility group box 1 (HMGB1) was correlated with pulmonary fibrosis. DMPM involves the malignant transformation of mesothelial cells, which originate from mesenchymal cells, similar to lung fibroblasts. Here, we investigated serum levels of HMGB1 in patients with MPM and compared them with those of a population that had been exposed to asbestos without developing MPM.

STUDY

The serum concentrations of HMGB1 were measured in 13 DMPM patients and 45 individuals with benign asbestos-related diseases.

RESULT

We demonstrated that the patients with DMPM had significantly higher serum levels of HMGB1 compared with the population who had been exposed to asbestos but did not develop DMPM.

CONCLUSION

Our data suggest that serum HMGB1 concentration is a useful serum marker for DMPM.

Double-positive expression of high-mobility group box 1 and vascular endothelial growth factor C indicates a poorer prognosis in gastric cancer patients

Background

Although many studies have indicated that high-mobility group box 1 protein (HMGB1) is associated with oncogenesis and a worse prognosis, the prognostic value of HMGB1 in gastric cancer (GC) remains unclear. In the present work, we aimed to evaluate the role of HMGB1 in GC and examined whether aberrant expression of both HMGB1 and vascular endothelial growth factor C (VEGF-C) increased the malignant potential of GC.

Methods

A total of 166 GC patients and 32 normal subjects were enrolled. HMGB1 and VEGF-C expression was detected by tissue microarrays (TMAs) and immunohistochemical staining. The correlation between HMGB1 and VEGF-C expression and their relationships with clinicopathological GC variables were examined. Univariate and multivariate analyses were performed using the Cox proportional hazard model to predict the factors related to the patients‘ overall survival rates.

Results

HMGB1 and VEGF-C expression were observed in 81 (48.80%) and 88 (53.01%) tumors, respectively, significantly higher than the rates among the corresponding controls. In addition, HMGB1 and VEGF-C expression were positively correlated (R² = 0.972). HMGB1 expression was also closely associated with tumor size, pT stage, nodal status, metastasis status, TNM stage, and poor prognosis. Multivariate survival analysis indicated that patients with HMGB1 and VEGF-C coexpression had the worst prognoses and survival rates (hazard ratio, 2.78; log rank P<0.001).

Conclusions

HMGB1 is commonly expressed in GC. Combined evaluation of HMGB1 and VEGF-C may serve as a valuable independent prognostic factor for GC patients.

Cardiovascular Disease and High-Mobility Group Box 1—Is a New Inflammatory Killer in Town?

High-mobility group box 1 (HMGB-1) is a nuclear protein physiologically involved in the maintaining of DNA structure in the nucleus. When tissue damage occurs, necrotic cells as well as inflammatory cells, once activated, release this protein in circulating blood, where it seems to exert a direct proinflammatory action. Thus, HMGB-1 might be involved in the pathophysiology of several diseases, including cardiovascular disease. However, the experimental evidence has not yet clarified its cardiovascular role which is still debated. Specifically, it is still not completely resolved whether HMGB-1 plays a protective or detrimental role on cardiovascular function. In this review, we consider the role of HMGB-1 in pathological conditions and comment on the role of this protein in the cardiovascular disease.

A functional yeast survival screen of tumor-derived cDNA libraries designed to identify anti-apoptotic mammalian oncogenes

Yeast cells can be killed upon expression of pro-apoptotic mammalian proteins. We have established a functional yeast survival screen that was used to isolate novel human anti-apoptotic genes overexpressed in treatment-resistant tumors. The screening of three different cDNA libraries prepared from metastatic melanoma, glioblastomas and leukemic blasts allowed for the identification of many yeast cell death-repressing cDNAs, including 28% of genes that are already known to inhibit apoptosis, 35% of genes upregulated in at least one tumor entity and 16% of genes described as both anti-apoptotic in function and upregulated in tumors. These results confirm the great potential of this screening tool to identify novel anti-apoptotic and tumor-relevant molecules. Three of the isolated candidate genes were further analyzed regarding their anti-apoptotic function in cell culture and their potential as a therapeutic target for molecular therapy. PAICS, an enzyme required for de novo purine biosynthesis, the long non-coding RNA MALAT1 and the MAST2 kinase are overexpressed in certain tumor entities and capable of suppressing apoptosis in human cells. Using a subcutaneous xenograft mouse model, we also demonstrated that glioblastoma tumor growth requires MAST2 expression. An additional advantage of the yeast survival screen is its universal applicability. By using various inducible pro-apoptotic killer proteins and screening the appropriate cDNA library prepared from normal or pathologic tissue of interest, the survival screen can be used to identify apoptosis inhibitors in many different systems.

p53-dependent release of Alarmin HMGB1 is a central mediator of senescent phenotypes

Cellular senescence irreversibly arrests proliferation in response to potentially oncogenic stress. Senescent cells also secrete inflammatory cytokines such as IL-6, which promote age-associated inflammation and pathology. HMGB1 (high mobility group box 1) modulates gene expression in the nucleus, but certain immune cells secrete HMGB1 as an extracellular Alarmin to signal tissue damage. We show that nuclear HMGB1 relocalized to the extracellular milieu in senescent human and mouse cells in culture and in vivo. In contrast to cytokine secretion, HMGB1 redistribution required the p53 tumor suppressor, but not its activator ATM. Moreover, altered HMGB1 expression induced a p53-dependent senescent growth arrest. Senescent fibroblasts secreted oxidized HMGB1, which stimulated cytokine secretion through TLR-4 signaling. HMGB1 depletion, HMGB1 blocking antibody, or TLR-4 inhibition attenuated senescence-associated IL-6 secretion, and exogenous HMGB1 stimulated NF-κB activity and restored IL-6 secretion to HMGB1-depleted cells. Our findings identify senescence as a novel biological setting in which HMGB1 functions and link HMGB1 redistribution to p53 activity and senescence-associated inflammation.

Serum HMGB1 as a prognostic marker for malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is an aggressive malignant tumor of mesothelial origin that shows a limited response to conventional chemotherapy and radiotherapy. Therefore, diagnosing MPM early is very important. Some researchers have previously reported that high-mobility group box 1 (HMGB1) was correlated with pulmonary fibrosis. MPM involves the malignant transformation of mesothelial cells, which originate from mesenchymal cells similar to lung fibroblasts. Here, we investigated serum levels of HMGB1 in patients with MPM and compared them with those of a population that had been exposed to asbestos without developing MPM.

Methods

HMGB1 production from MPM cell lines was measured using ELISA. Serum HMGB1 levels were also examined in 61 MPM patients and 45 individuals with benign asbestos-related diseases.

Results

HMGB1 concentrations of 2 out of 4 MPM cell lines were higher than that of normal mesothelial cell line, Met-5A. We demonstrated that patients with MPM had significantly higher serum levels of HMGB1 than the population who had been exposed to asbestos but had not developed MPM. The difference in overall survival between groups with serum HMGB1 levels that were lower and higher than assumed cut-off values was significant.

Conclusions

Our data suggest that serum HMGB1 concentration is a useful prognostic factor for MPM.

Specific siRNA targeting receptor for advanced glycation end products (RAGE) decreases proliferation in human breast cancer cell lines

Receptor for Advanced Glycation End Products (RAGE) is an oncogenic trans-membranous receptor overexpressed in various human cancers. However, the role of RAGE in breast cancer development and proliferation is still unclear. In this study, we demonstrated that RAGE expression levels are correlated to the degree of severity of breast cancer. Furthermore, there is a decrease in the proliferation of all sub-types of breast cancer, MCF-7, SK-Br-3 and MDA-MB-231, as a result of the effect of RAGE siRNA. RAGE siRNA arrested cells in the G1 phase and inhibited DNA synthesis (p < 0.05). Moreover, qRT-PCR and Western Blot results demonstrated that RAGE siRNA decreases the expression of transcriptional factor NF-κB p65 as well as the expression of cell proliferation markers PCNA and cyclinD1. RAGE and RAGE ligands can thus be considered as possible targets for breast cancer management and therapy.

Oxidized extracellular DNA as a stress signal in human cells

The term "cell-free DNA" (cfDNA) was recently coined for DNA fragments from plasma/serum, while DNA present in in vitro cell culture media is known as extracellular DNA (ecDNA). Under oxidative stress conditions, the levels of oxidative modification of cellular DNA and the rate of cell death increase. Dying cells release their damaged DNA, thus, contributing oxidized DNA fragments to the pool of cfDNA/ecDNA. Oxidized cell-free DNA could serve as a stress signal that promotes irradiation-induced bystander effect. Evidence points to TLR9 as a possible candidate for oxidized DNA sensor. An exposure to oxidized ecDNA stimulates a synthesis of reactive oxygen species (ROS) that evokes an adaptive response that includes transposition of the homologous loci within the nucleus, polymerization and the formation of the stress fibers of the actin, as well as activation of the ribosomal gene expression, and nuclear translocation of NF-E2 related factor-2 (NRF2) that, in turn, mediates induction of phase II detoxifying and antioxidant enzymes. In conclusion, the oxidized DNA is a stress signal released in response to oxidative stress in the cultured cells and, possibly, in the human body; in particular, it might contribute to systemic abscopal effects of localized irradiation treatments.

Targeting HMGB1 inhibits ovarian cancer growth and metastasis by lentivirus-mediated RNA interference

High-mobility group box 1 (HMGB1), a nuclear and extracellular protein, is implicated in the development and progression of some types of cancers. However, no information is available to date regarding the function of HMGB1 in ovarian cancer. In this study, we performed cDNA microarray analysis and identified HMGB1 as a gene dramatically elevated in the highly invasive subclone S1 compared with the low invasive subclone S21 derived from the same cell line SKOV3. Then lentivirus vector with HMGB1 shRNA was constructed and infected the highly invasive cell line S1, A1, and HO8910PM. Real-time RT-PCR, Western blot, and IHC results confirmed the down-regulation of HMGB1 expression by its shRNA was about 80-90% at both the mRNA and protein levels. Knockdown of HMGB1 significantly suppressed ovarian cancer cell proliferation and induced cell cycle arrest at the G1/G0 phase, which was accompanied by decreased expressions of cyclin D1 and PCNA. Furthermore, knockdown of HMGB1 induced ovarian cancer cell apoptosis, which was mediated by increased expression of Bax and decreased expression of Bcl-2. Finally, knockdown of HMGB1 significantly inhibited ovarian cancer cell invasion and metastasis, which was regulated by decreased expressions of MMP2 and MMP9. Serum HMGB1 levels in patients with epithelial ovarian cancer were significantly higher than that in patients with benign ovarian tumor and healthy controls. These results indicate that HMGB1 is a newly identified gene associated with ovarian cancer growth and metastasis. HMGB1 may serve as a new therapeutic target for the treatment of ovarian cancer in the future.

Alarmins: awaiting a clinical response

Alarmins are endogenous molecules that are constitutively available and released upon tissue damage and activate the immune system. Current evidence indicates that uncontrolled and excessive release of alarmins contributes to the dysregulated processes seen in many inflammatory and autoimmune conditions, as well as tumorigenesis and cancer spread. Conversely, alarmins have also been found to play a major role in the orchestration of tissue homeostasis, including repair and remodeling in the heart, skin, and nervous system. Here, we provide an update and overview on alarmins, highlighting the areas that may benefit from this clinical translation.

Saccharomyces cerevisiae as a model system to study the response to anticancer agents

The development of new strategies for cancer therapeutics is indispensable for the improvement of standard protocols and the creation of other possibilities in cancer treatment. Yeast models have been employed to study numerous molecular aspects directly related to cancer development, as well as to determine the genetic contexts associated with anticancer drug sensitivity or resistance. The budding yeast Saccharomyces cerevisiae presents conserved cellular processes with high homology to humans, and it is a rapid, inexpensive and efficient compound screening tool. However, yeast models are still underused in cancer research and for screening of antineoplastic agents. Here, the employment of S. cerevisiae as a model system to anticancer research is discussed and exemplified. Focusing on the important determinants in genomic maintenance and cancer development, including DNA repair, cell cycle control and epigenetics, this review proposes the use of mutant yeast panels to mimic cancer phenotypes, screen and study tumor features and synthetic lethal interactions. Finally, the benefits and limitations of the yeast model are highlighted, as well as the strategies to overcome S. cerevisiae model limitations.

HMGB1 was a pivotal synergistic effecor for CpG oligonucleotide to enhance the progression of human lung cancer cells

High-mobility group box 1 (HMGB1) has been implicated in a variety of biologically important processes, including transcription, DNA repair, differentiation, development, and extracellular signaling. However, the potential role of HMGB1 in tumor biology still remains intractable. Our previous study showed that TLR9 response to CpG oligonucleotide (ODN) in 95D human lung cancer cells could enhance their growth and invasive potential in vitro and in vivo. Here we found that CpG ODN stimulation to 95D cells induced the secretion of HMGB1 in a dose dependent manner. We further showed that blockade of extracellular HMGB1 using A box peptide and ethyl pyruvate significantly abrogated the CpG ODN enhanced progression of 95D cells. Interestingly, we found that HMGB1 alone or acted synergistic with CpG ODN could enhance the progression of 95D cells. Notably, we revealed that RAGE and TLR4 were critical for HMGB1 to exert the synergistic function. We observed a MyD88-dependent upregulation of matrix metalloproteinase (MMP) 2, MMP9 and cyclin-dependent kinase (CDK) 2 in 95D cells in response to HMGB1. These findings might further our understanding of TLR9 signaling in tumor biology and be helpful for developing HMGB1-based strategy against lung cancer.

High-mobility group protein B1 (HMGB1) is a novel biomarker for human ovarian cancer

BACKGROUND

High mobility group box l (HMGB1), a nuclear and extracellular protein, is implicated in some physiologic and pathologic conditions. In this study, we investigated the expression and function of HMGB1 in ovarian cancer.

METHODS

cDNA microarray analysis was performed to compare gene expression profiles of the highly invasive and the low invasive subclones derived from the SKOV3 human ovarian cancer cell line. Immunohistochemistry (IHC) staining was performed to investigate HMGB1 expression in a total of 100 ovarian tissue specimens. In functional assays, effects of HMGB1 knockdown on the biological behavior of ovarian cancer cells were investigated.

RESULTS

HMGB1 was overexpressed in the highly invasive subclone compared with the low invasive subclone. High HMGB1 expression was associated with poor clinicopathologic features. Knockdown of HMGB1 expression significantly suppressed ovarian cancer cell proliferation accompanied by decreased cyclin D1 and PCNA expression, and inhibited cell migration and invasion accompanied by decreased MMP2 and MMP9 activities.

CONCLUSION

HMGB1 is a newly identified gene overexpressed in ovarian cancer and associated with poor clinicopathologic features. HMGB1 may serve as a new biomarker and a therapeutic target for ovarian cancer in the future.

The Apaf-1-binding protein Aven is cleaved by Cathepsin D to unleash its anti-apoptotic potential

The anti-apoptotic molecule Aven was originally identified in a yeast two-hybrid screen for Bcl-x(L)-interacting proteins and has also been found to bind Apaf-1, thereby interfering with Apaf-1 self-association during apoptosome assembly. Aven is expressed in a wide variety of adult tissues and cell lines, and there is increasing evidence that its overexpression correlates with tumorigenesis, particularly in acute leukemias. The mechanism by which the anti-apoptotic activity of Aven is regulated remains poorly understood. Here we shed light on this issue by demonstrating that proteolytic removal of an inhibitory N-terminal Aven domain is necessary to activate the anti-apoptotic potential of the molecule. Furthermore, we identify Cathepsin D (CathD) as the protease responsible for Aven cleavage. On the basis of our results, we propose a model of Aven activation by which its N-terminal inhibitory domain is removed by CathD-mediated proteolysis, thereby unleashing its cytoprotective function.

Inflammation and immune surveillance in cancer

Chronic inflammation is a risk factor for tumor development. However, understanding the effect of the immune system on tumor development has only been significantly advanced over the past two decades. We now appreciate that the immune system, in addition to tumor-suppressive function by eliminating nascent transformed tumor cells, can also exert selection pressure on tumor cells and facilitate tumor growth by providing a favorable tumor microenvironment. Yet, the distinctions between tumor-promoting inflammation and tumor-suppressive immunity are still not clear due to the dual role of some cytokines and other molecules in the immune system. The danger signal hypothesis has shaped our view of the role of immunity in cancer development, but still little is known about the exact role of danger signal receptors in cancer progression. In this review, we introduce the processes of cancer immunoediting and inflammation-induced cancer and discuss what is currently known about the role of danger signal receptors in cancer development and progression.

TNF-α induced secretion of HMGB1 from non-immune canine mammary epithelial cells (MTH53A)

BACKGROUND

Mammary neoplasias are one of the most frequent and spontaneously occurring malignancies in dogs and humans. Due to the similar anatomy of the mammary gland in both species, the dog has become an important animal model for this cancer entity. In human breast carcinomas, the overexpression of a protein named high-mobility group box 1 (HMGB1) was reported. Cells of the immune system were described to release HMGB1 actively exerting cytokine function. Thereby it is involved in the immune system activation, tissue repair, and cell migration. Passive release of HMGB1 by necrotic cells at sites of tissue damage or in necrotic hypoxic regions of tumors induces cellular responses e.g. release of proinflammatory cytokines leading to elevated inflammatory response and neo-vascularization of necrotic tumor areas. Herein we investigated if a time-dependent stimulation with the separately applied proinflammatory cytokines TNF-α and IFN-γ can cause secretion of HMGB1 in a non-immune related HMGB1-non-secreting epithelial canine mammary cell line (MTH53A) derived from non-neoplastic tissue.

METHODS

The canine cell line was transfected with recombinant HMGB1 bicistronic expression vectors and stimulated after transfection with the respective cytokine independently for 6, 24 and 48 h. HMGB1 protein detection was performed by Western blot analysis and quantified a by enzyme-linked immunosorbent assay. Live cell laser scanning multiphoton microscopy of MTH53A cells expressing a HMGB1-GFP fusion protein was performed in order to examine, if secretion of HMGB1 under cytokine stimulating conditions is also visible by fluorescence imaging.

RESULTS

The observed HMGB1 release kinetics showed a clearly time-dependent manner with a peak release 24h after TNF-α stimulation, while stimulation with IFN-γ had only small effects on the HMGB1 release. Multiphoton HMGB1 live cell microscopy showed diffuse cell membrane structure changes 29 h after cytokine-stimulation but no clear secretion of HMGB1-GFP after TNF-α stimulation was visible.

CONCLUSION

Our results demonstrate that non-immune HMGB1-non-secreting cells of epithelial origin derived from mammary non-neoplastic tissue can be induced to release HMGB1 by single cytokine application. This indicates that tumor and surrounding tissue can be stimulated by tumor present inflammatory and necrotic cytokines to release HMGB1 acting as neo-vascularizing factor thus promoting tumor growth.

Effect of HMGB1 silencing on cell proliferation, invasion and apoptosis of MGC-803 gastric cancer cells

High-mobility group box 1 (HMGB1) is a multifunctional protein with intranuclear and extracellular functions. Although HMGB1 is overexpressed in approximately 85% of gastric cancers, the role of HMGB1 in gastric cancer biology remains unclear. In this study, we investigate the effect of downregulation of HMGB1 on the biological behavior of gastric cancer cells. MGC-803 gastric cancer cells were transduced with HMGB1-specific RNAi lentiviral vectors. Real-time polymerase chain reaction and Western blot analysis of HMGB1 mRNA and protein, respectively, validated the silencing effects. HMGB1-specific silencing significantly decreased cell proliferation. The impact on proliferation was observed at the cell cycle level--the number of cells in the G0/G1 phase increased, whereas that in S and G2/M phases decreased. Cell cycle changes were accompanied by decreases in cyclin D1 expression. Furthermore, HMGB1 silencing sensitized cells to apoptosis that was induced by oxaliplatin and mediated by the caspase-3 pathway. Finally, silencing of HMGB1 expression significantly reduced cellular metastatic ability and MMP-9 expression in MGC-803 cells. In summary, HMGB1 not only plays an essential role in the proliferation and invasion of MGC-803 cells but also represents a potential target for the therapeutic intervention of gastric cancer.

High-mobility group box 1 is associated with clinicopathologic features in patients with hepatocellular carcinoma

High-mobility group box 1(HMGB1) has been associated with many human cancers, but the role of HMGB1 in hepatocellular carcinoma (HCC) remains unclear. The aim of this study is to investigate the expression of HMGB1 in human HCC with regard to its clinical significance. Twelve cases of normal liver tissues, 34 cases of HCC and the corresponding liver tissue just around the tumor (LAT) were collected. Then, all the samples were subjected to clinicopathologic examination, reverse transcription-polymerase chain reaction (RT-PCR), Western-blot (WB) and immunohistochemical analysis for the expression of HMGB1. The relationships between HMGB1 mRNA expression and clinicopathologic parameters were analyzed. RT-PCR demonstrated that the expression of relative HMGB1 mRNA (HMGB1/GAPDH) was 0.854 ± 0.172; the highest in the tissue of HCC, significantly up-regulated compared with that of 0.527 ± 0.155 in LAT and of 0.405 ± 0.087 in normal liver tissues (P < 0.001). HMGB1 mRNA overexpression was significantly associated with Edmondson stage, TNM stage, vascular invasion and capsule invasion. Western-blot showed the expression of HMGB1 protein in HCC also as the highest among all the groups. Furthermore this overexpression revealed by immunostaining was predominantly localized in the nuclei of HCC; whereas, none of the stains were seen in normal liver cells and only a trace of it was detected in the cytoplasm of LAT cells. Our results suggested the overexpression of HMGB1 might be an important pathogenetic factor in HCC. The mechanisms of HMGB1 in HCC genesis, development and its possible diagnostic and prognostic roles need to be further explored.

Production of recombinant human HMGB1 and anti-HMGB1 rabbit serum

High-mobility group box-1 (HMGB1) plays important roles in inflammation, immune responses, and tumor progression. Since HMGB1 and its components have been shown to be mediators of a number of diseases but several sources of recombinant HMGB1 showed controversial biological activity, it is important to obtain recombinant HMGB1 with properties that resemble the native protein. For this purpose, we cloned genes coding for human HMGB1 and its active components A box and B box by PCR and inserted the cloned genes into pET28a vectors for transformation of Escherichia coli BL21. The E. coli expressed proteins were then purified with a Ni(2+)-NTA column and the endotoxin content was removed. Recombinant human HMGB1 (rhHMGB1) and its B box thus obtained stimulated, but A box inhibited, the production of the chemokine CXCL8/IL-8 by THP-1 monocytic cell line. We also used purified rhHMGB1 to immunize rabbits and generated potent anti-sera, which was capable of neutralizing the activity of rhHMGB1 in vitro and detecting the increased HMGB1 expression in inflammatory tissues in mice and humans. Thus, we have established essential means to produce biologically active rhHMGB1 that will facilitate us to study its role in diseases and to explore its potential as a therapeutic agent.

Expanding the paradigm for estrogen receptor binding and transcriptional activation

Estrogen receptor (ER) binds to a spectrum of functional estrogen response elements (ERE) within the human genome, including ERE half-sites (HERE), inverted and direct repeats. This has been confounding, because ER has been reported to bind weakly, if at all, to these sites in vitro. We show that ER binds strongly to these nonconventional EREs, and the binding is enhanced by the presence of high-mobility group protein B1 (HMGB1). Collectively, these and previous findings reinforce the notion of the plasticity of strong ER/ERE interactions, consistent with their broader range of observed binding specificity. In addition, transient transfection studies using luciferase reporter gene assays show that these EREs drive luciferase activity, and HMGB1 enhances transcriptional activity. Furthermore, HMGB1 gene expression knockdown results in a precipitous drop in luciferase activity, suggesting a prominent role for HMGB1 in activation of estrogen/ER-responsive genes. Therefore, these data advocate that the minimal target site for ER is a cHERE (consensus HERE) that occurs in many different contexts and that HMGB1 enhances both the binding affinity and transcriptional activity. This challenges the current paradigm for ER binding affinity and functional activity and suggests that the paradigm requires significant reevaluation and modification. These findings also suggest a possible mechanism for a cross talk between genes regulated by ER and class II nuclear receptors.

High-mobility group box-1 mediates toll-like receptor 4-dependent angiogenesis

OBJECTIVE

Inflammation is closely linked to angiogenesis, and Toll-like receptors (TLRs) are the key mediators of inflammatory responses. However, the impact of TLRs on angiogenesis is incompletely understood. In this study, we determined the involvement of TLRs in angiogenesis.

METHODS AND RESULTS

In a mouse model of alkali-induced corneal neovascularization (CNV), we found that CNV was attenuated in TLR4-/- but not TLR2-/- mice. Further study revealed that the absence of TLR4 led to decreased production of proangiogenic factors in association with reduced accumulation of macrophages at the site of wounds, which was associated with reduced expression of high-mobility group box-1 (HMGB1) protein, an endogenous ligand for TLR4. Topical application of HMGB1 to the injured cornea promoted CNV with increased macrophage accumulation in wild-type mice but not in TLR4-/- mice. HMGB1 treatment in vitro also promoted the production of proangiogenic factors by mouse macrophages in a TLR4-dependent manner. Furthermore, antagonists of HMGB1 and TLR4 reduced CNV and macrophage recruitment in the injured cornea of wild-type mice.

CONCLUSIONS

Our results suggest that the release of HMGB1 in the wounds initiates TLR4-dependent responses that contribute to neovascularization. Thus, targeting HMGB1-TLR4 signaling cascade may constitute a novel therapeutic approach to angiogenesis-related diseases.

Analysis and verification of the HMGB1 signaling pathway

BACKGROUND

Recent studies have found that overexpression of the High-mobility group box-1 (HMGB1) protein, in conjunction with its receptors for advanced glycation end products (RAGEs) and toll-like receptors (TLRs), is associated with proliferation of various cancer types, including that of the breast and pancreatic.

RESULTS

We have developed a rule-based model of crosstalk between the HMGB1 signaling pathway and other key cancer signaling pathways. The model has been simulated using both ordinary differential equations (ODEs) and discrete stochastic simulation. We have applied an automated verification technique, Statistical Model Checking, to validate interesting temporal properties of our model.

CONCLUSIONS

Our simulations show that, if HMGB1 is overexpressed, then the oncoproteins CyclinD/E, which regulate cell proliferation, are overexpressed, while tumor suppressor proteins that regulate cell apoptosis (programmed cell death), such as p53, are repressed. Discrete, stochastic simulations show that p53 and MDM2 oscillations continue even after 10 hours, as observed by experiments. This property is not exhibited by the deterministic ODE simulation, for the chosen parameters. Moreover, the models also predict that mutations of RAS, ARF and P21 in the context of HMGB1 signaling can influence the cancer cell's fate - apoptosis or survival - through the crosstalk of different pathways.

High-mobility group box 1 and cancer

High-mobility group box 1 protein (HMGB1), a chromatin associated nuclear protein and extracellular damage associated molecular pattern molecule (DAMP), is an evolutionarily ancient and critical regulator of cell death and survival. Overexpression of HMGB1 is associated with each of the hallmarks of cancer including unlimited replicative potential, ability to develop blood vessels (angiogenesis), evasion of programmed cell death (apoptosis), self-sufficiency in growth signals, insensitivity to inhibitors of growth, inflammation, tissue invasion and metastasis. Our studies and those of our colleagues suggest that HMGB1 is central to cancer (abnormal wound healing) and many of the findings in normal wound healing as well. Here, we focus on the role of HMGB1 in cancer, the mechanisms by which it contributes to carcinogenesis, and therapeutic strategies based on targeting HMGB1.

Clinical value of serum HMGB1 levels in early detection of recurrent squamous cell carcinoma of uterine cervix: comparison with serum SCCA, CYFRA21-1, and CEA levels

AIM

To evaluate the clinical value of serum high mobility group box chromosomal protein 1 (HMGB1) levels in making the early diagnosis of recurrent cervical squamous cell carcinomas (CSCC) and compare it with the value of serum squamous cell carcinoma antigen (SCCA), cytokeratin fragment (CYFRA) 21-1, and carcinoembryonic antigen (CEA) levels.

METHODS

Immunohistochemical staining of tissue from 64 patients with recurrent CSCCs, 72 patients with non-recurrent carcinoma, and 28 healthy participants was performed to determine the expression of HMGB1 protein. The serum levels of the 4 markers in 112 patients with recurrent CSCC, 174 patients with non-recurrent disease, and 128 healthy participants were measured by enzyme-linked immunosorbent assay. The receiver operating characteristic (ROC) curves were constructed and the area under the curve (AUC) was calculated.

RESULTS

Higher immunostaining score was found in recurrent CSCC tissue sections than in non-recurrent CSCC sections. Serum HMGB1 levels in patients with recurrent CSCC were significantly higher than in patients with non-recurrent disease and healthy controls. The AUC of HMGB1, SCCA, CYFRA21-1, and CEA was 0.816, 0.768, 0.703, and 0.625, respectively. HMGB1 had the best specificity and positive likelihood ratio (78.0% and 3.25, respectively), whereas SCCA had the best sensitivity and negative likelihood ratio (76.3% and 0.34, respectively). Parallel combined measurements increased the diagnostic sensitivity and serial combination increased the specificity. High serum HMGB1 levels were inversely correlated with disease-free survival (P=0.009, Pearson chi(2) test) and overall survival (P=0.018).

CONCLUSION

HMGB1 was overexpressed in recurrent CSCCs. Serum HMGB1 level could be a useful and specific marker for evaluating the disease recurrence and predicting prognosis in patients with CSCC. Serial combined measurements of serum HMGB1, SCCA, and CYFRA21-1 increased the diagnostic specificity, and parallel combined testing increased the diagnostic sensitivity.

Overexpression of the far upstream element binding protein 1 in hepatocellular carcinoma is required for tumor growth

We identified the far upstream element binding protein 1 (FBP1), an activator of transcription of the proto-oncogene c-myc, in a functional yeast survival screen for tumor-related antiapoptotic proteins and demonstrated strong overexpression of FBP1 in human hepatocellular carcinoma (HCC). Knockdown of the protein in HCC cells resulted in increased sensitivity to apoptotic stimuli, reduced cell proliferation, and impaired tumor formation in a mouse xenograft transplantation model. Interestingly, analysis of gene regulation in these cells revealed that c-myc levels were not influenced by FBP1 in HCC cells. Instead, we identified the cell cycle inhibitor p21 as a direct target gene repressed by FBP1, and in addition, expression levels of the proapoptotic genes tumor necrosis factor alpha, tumor necrosis factor-related apoptosis-inducing ligand, Noxa, and Bik were elevated in the absence of FBP1.

CONCLUSION

Our data establish FBP1 as an important oncoprotein overexpressed in HCC that induces tumor propagation through direct or indirect repression of cell cycle inhibitors and proapoptotic target genes.

HMGB1 and HMGB2 proteins up-regulate cellular expression of human topoisomerase IIalpha

Topoisomerase IIα (topo IIα) is a nuclear enzyme involved in several critical processes, including chromosome replication, segregation and recombination. Previously we have shown that chromosomal protein HMGB1 interacts with topo IIα, and stimulates its catalytic activity. Here we show the effect of HMGB1 on the activity of the human topo IIα gene promoter in different cell lines. We demonstrate that HMGB1, but not a mutant of HMGB1 incapable of DNA bending, up-regulates the activity of the topo IIα promoter in human cells that lack functional retinoblastoma protein pRb. Transient over-expression of pRb in pRb-negative Saos-2 cells inhibits the ability of HMGB1 to activate the topo IIα promoter. The involvement of HMGB1 and its close relative, HMGB2, in modulation of activity of the topo IIα gene is further supported by knock-down of HMGB1/2, as evidenced by significantly decreased levels of topo IIα mRNA and protein. Our experiments suggest a mechanism of up-regulation of cellular expression of topo IIα by HMGB1/2 in pRb-negative cells by modulation of binding of transcription factor NF-Y to the topo IIα promoter, and the results are discussed in the framework of previously observed pRb-inactivation, and increased levels of HMGB1/2 and topo IIα in tumors.

Aging-related loss of the chromatin protein HMGB2 in articular cartilage is linked to reduced cellularity and osteoarthritis

Osteoarthritis (OA) is the most common joint disease and typically begins with an aging-related disruption of the articular cartilage surface. Mechanisms leading to the aging-related cartilage surface degeneration remain to be determined. Here, we demonstrate that nonhistone chromatin protein high-mobility group box (HMGB) protein 2 is uniquely expressed in the superficial zone (SZ) of human articular cartilage. In human and murine cartilage, there is an aging-related loss of HMGB2 expression, ultimately leading to its complete absence. Mice genetically deficient in HMGB2 (Hmgb2(-/-)) show earlier onset of and more severe OA. This is associated with a profound reduction in cartilage cellularity attributable to increased cell death. These cellular changes precede glycosaminoglycan depletion and progressive cartilage erosions. Chondrocytes from Hmgb2(-/-) mice are more susceptible to apoptosis induction in vitro. In conclusion, HMGB2 is a transcriptional regulator specifically expressed in the SZ of human articular cartilage and supports chondrocyte survival. Aging is associated with a loss of HMGB2 expression and reduced cellularity, and this contributes to the development of OA.