A novel function of the receptor for advanced glycation end-products (RAGE) in association with tumorigenesis and tumor differentiation of HCC

Soluble receptor for advanced glycation end products and liver stiffness in postoperative biliary atresia

OBJECTIVES

Soluble receptor for advanced glycation end products (sRAGE) has emerged as a possible biomarker of several disease conditions, including liver injury. This study was aimed to assess serum sRAGE and liver stiffness in biliary atresia (BA).

DESIGN AND METHODS

Forty postoperative BA patients and 20 controls were enrolled. Serum sRAGE levels were analyzed by enzyme-linked immunosorbent assay. Liver stiffness scores were measured by transient elastography.

RESULTS

BA patients had higher serum sRAGE and liver stiffness values than controls (P<0.001). Serum sRAGE and liver stiffness values were significantly elevated in BA patients with jaundice compared to those without jaundice (P<0.001). Additionally, serum sRAGE was correlated with liver stiffness and serum total bilirubin (r=0.65, P<0.001 and r=0.71, P<0.001, respectively).

CONCLUSION

Serum sRAGE was associated with the severity of BA. Accordingly, serum sRAGE and liver stiffness may serve as indicators reflecting the severity and the development of hepatic fibrosis in postoperative BA.

Predictive value of immunogenic cell death biomarkers HMGB1, sRAGE, and DNase in liver cancer patients receiving transarterial chemoembolization therapy

Transarterial chemoembolization (TACE) therapy is an effective locoregional anticancer treatment for liver cancer patients. Serum biomarkers involved in immunogenic cell death may be valuable for early predicting therapy response and estimating prognosis. Sera of 50 prospectively and consecutively included hepatocellular carcinoma (HCC) patients, undergoing TACE therapy, were taken before and 24 h after TACE application. In these samples, soluble biomarkers involved in immunogenic cell death, and among them, high-mobility group box 1 (HMGB1), soluble receptor of advanced glycation end products (sRAGE), and DNase activity were measured. They were compared with radiological response to therapy. A total of 71 TACE therapies were evaluated, of which 32 were classified as "no progression," and 39, as "progression." While HMGB1 levels increased already 24 h after TACE, there was an early decrease of sRAGE and DNase activity. Pretherapeutic and 24-h values of sRAGE were significantly higher in the no progression group than those in the progression group. There was no difference with respect to treatment response for DNase and HMGB1. Soluble RAGE is a new parameter with predictive relevance in primary liver cancer patients undergoing TACE therapy.

IL-33 and HMGB1 alarmins: sensors of cellular death and their involvement in liver pathology

'Alarmins' are a group of proteins or molecules that are released from cells during cellular demise to alert the host immune system. Two of them, Interleukin-33 (IL-33) and high-mobility group box-1 (HMGB1), share many similarities of cellular localization, functions and involvement in various inflammatory pathologies including hepatitis. The expressions of IL-33 and HMGB1, and their receptors ST2 and receptor for advanced glycation end products (RAGE), are substantially up-regulated during acute and chronic hepatitis. Recent data evidence a possible protective role of IL-33/ST2 axis during liver injury. A contrast in expression of IL-33 and HMGB1 alarmins were associated with type of hepatocellular death mediated by immune cells or hepato-toxic agents. The massive release of active form of IL-33 from hepatocytes may affect the recruitment and activation of its ST2-positive target immune cells in the liver to confer its alarmin functions. This review highlights the emerging roles of alarmin proteins in various liver pathologies, by focusing on classical HMGB1 and a newly discovered alarmin, the IL-33.

Glycer-AGEs-RAGE signaling enhances the angiogenic potential of hepatocellular carcinoma by upregulating VEGF expression

AIM: To investigate the effect of glyceraldehyde-derived advanced glycation end-products (Glycer-AGEs) on hepatocellular carcinoma (HCC) cells.

METHODS: Two HCC cell lines (Hep3B and HepG2 cells) and human umbilical vein endothelial cells (HUVEC) were used. Cell viability was determined using the WST-8 assay. Western blotting, enzyme linked immunosorbent assay, and real-time reverse transcription-polymerase chain reactions were used to detect protein and mRNA. Angiogenesis was evaluated by assessing the proliferation, migration, and tube formation of HUVEC.

RESULTS: The receptor for AGEs (RAGE) protein was detected in Hep3B and HepG2 cells. HepG2 cells were not affected by the addition of Glycer-AGEs. Glycer-AGEs markedly increased vascular endothelial growth factor (VEGF) mRNA and protein expression, which is one of the most potent angiogenic factors. Compared with the control unglycated bovine serum albumin (BSA) treatment, VEGF mRNA expression levels induced by the Glycer-AGEs treatment were 1.00 ± 0.10 vs 1.92 ± 0.09 (P < 0.01). Similarly, protein expression levels induced by the Glycer-AGEs treatment were 1.63 ± 0.04 ng/mL vs 2.28 ± 0.17 ng/mL for the 24 h treatment and 3.36 ± 0.10 ng/mL vs 4.79 ± 0.31 ng/mL for the 48 h treatment, respectively (P < 0.01). Furthermore, compared with the effect of the control unglycated BSA-treated conditioned medium, the Glycer-AGEs-treated conditioned medium significantly increased the proliferation, migration, and tube formation of HUVEC, with values of 122.4% ± 9.0% vs 144.5% ± 11.3% for cell viability, 4.29 ± 1.53 vs 6.78 ± 1.84 for migration indices, and 71.0 ± 7.5 vs 112.4 ± 8.0 for the number of branching points, respectively (P < 0.01).

CONCLUSION: These results suggest that Glycer-AGEs-RAGE signaling enhances the angiogenic potential of HCC cells by upregulating VEGF expression.

The Role of receptor for Advanced Glycation End Products (RAGE) in the proliferation of hepatocellular carcinoma

The receptor for advanced glycation end products (RAGE) is oncogenic and overexpressed in human cancers, but its role in hepatocellular carcinoma remains unclear. Here we demonstrated that RAGE is overexpressed in primary hepatocellular carcinoma (PHC) compared to adjacent para-neoplastic liver samples. Serum endogenous secretory RAGE levels were also increased in PHC patients (p < 0.01). Moreover, we demonstrated that RAGE regulates cellular proliferation in Hepatocellular carcinoma (HCC). Knockdown of RAGE by specific siRNA inhibited cellular growth in the hepatocellular carcinoma cell line, Huh7, whereas the RAGE ligand, high mobility group box 1 protein (HMGB1) increased cellular proliferation. In addition, knockdown of RAGE by siRNA arrested cells in the G1 phase and inhibited DNA synthesis (p < 0.01), while HMGB1 protein decreased the number of cells in the G1 phase and increased the number in the S phase (p < 0.05). Furthermore, quantitative real time RT-PCR (qRT-PCR) and Western Blot results demonstrated that RAGE and HMGB1 positively regulate NF-κB p65 expression in Huh7 cells. These studies suggest that RAGE and RAGE ligands are important targets for therapeutic intervention in hepatocellular carcinoma.

The Receptor for Advanced Glycation End-products (RAGE) protects pancreatic tumor cells against oxidative injury

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), can cause toxicity and act as signaling molecules in various pathways regulating both cell survival and cell death. However, the sequence of events between the oxidative insult and cell damage remains unclear. In the current study, we investigated the effect of oxidative stress on activation of the Receptor for Advanced Glycation End-products (RAGE) and subsequent protection against H(2)O(2)-induced pancreatic tumor cell damage. We found that exposure of pancreatic tumor cells to H(2)O(2) provoked a nuclear factor kappa B (NF-κB)-dependent increase in RAGE expression. Further, suppression of RAGE expression by RNA interference increased the sensitivity of pancreatic tumor cells to oxidative injury. Furthermore, targeted knockdown of RAGE led to increased cell death by apoptosis and diminished cell survival by autophagy during H(2)O(2)-induced oxidative injury. Moreover, we demonstrate that RAGE is a positive feedback regulator for NF-κB as knockdown of RAGE decreased H(2)O(2)-induced activity of NF-κB. Taken together, these results suggest that RAGE is an important regulator of oxidative injury.

Diabetes and cancer: Looking at the multiligand/RAGE axis

The association between diabetes and hyperglycemia and the associated increased risk of several solid and hematologic malignancies has been the subject of investigation for many years. Although the association is not fully understood, current knowledge clearly indicates that diabetes may influence malignant cell transformation by several mechanisms, including hyperinsulinemia, hyperglycemia and chronic inflammation. In this context, the receptor for advanced glycation end-products (RAGE) has emerged as a focal point in its contribution to malignant transformation and tumor growth. We highlight how RAGE, once activated, as it manifests itself in conditions such as diabetes or hyperglycemia, is able to continuously bring about an inflammatory milieu, thus supporting the contribution of chronic inflammation to the development of malignancies.

What is the role of the receptor for advanced glycation end products-ligand axis in liver injury?

Multiligand receptor for advanced glycation end products (RAGE) is expressed in a wide variety of tissues, including the liver. Interactions with its ligands lead to cellular activation and thus prolonged inflammation and apoptosis. RAGE also exists in a soluble, truncated isoform called soluble RAGE, which has the same ligand-binding specificity as membrane-RAGE; acting as decoy, it can contribute to the removal/neutralization of circulating ligands and the resultant reduction of signaling pathway activation. Experimental and clinical studies have highlighted the idea that the RAGE-ligand axis is involved in the development of liver fibrosis, inflammation, and regeneration after a massive injury and in the setting of liver transplantation. The involvement of the RAGE-ligand axis in vascular disease, diabetes, cancer, and neurodegeneration is well established, but it still needs to be clarified in the setting of liver diseases. We present a review of the recent literature on this receptor in surgical and clinical settings involving the liver, and we highlight the open issues and possible directions of future research.

MK615 decreases RAGE expression and inhibits TAGE-induced proliferation in hepatocellular carcinoma cells

AIM: To investigate the proliferative effect of advanced glycation end-products (AGEs) and the role of their cellular receptor (RAGE) on hepatocellular carcinoma (HCC) cells, and the inhibitory effects of MK615, an extract from Japanese apricot, against AGEs were also evaluated.

METHODS: Two HCC cell lines, HuH7 and HepG2, were used. Expression of RAGE was investigated by polymerase chain reaction, Western blotting, and flow cytemetry (FACS). The effect of MK615 on RAGE expression was also evaluated by FACS. The proliferative effects of a control (unglycated bovine serum albumin), glucose-derived AGEs (Glc-AGE), and glyceraldehyde-derived AGEs (Glycer-AGE), and the anti-proliferative effect of MK615 against AGEs, were evaluated using MTT assays.

RESULTS: Expression of RAGE was confirmed at both the mRNA and protein levels in both HuH7 and HepG2. FACS revealed that the level of RAGE expression was higher in HuH7 than in HepG2. Treatment with 0.1 μg/mL MK615 decreased the expression level of RAGE from 24.3% to 3.7% in HuH7 and from 6.2% to 4.8% in HepG2. The growth indices for the control, Glc-AGE, and Glycer-AGE were 1.06 ± 0.08, 0.99 ± 0.04, and 1.38 ± 0.05, respectively, in HuH7 (P = 0.037), and were 1.03 ± 0.04, 1.04 ± 0.03, and 1.07 ± 0.05, respectively, in HepG2 (P > 0.05). When the cells were cultured simultaneously with Glycer-AGE and MK615, MK615 abrogated the proliferative effect of Glycer-AGE in HuH7.

CONCLUSION: Only Glycer-AGE has a proliferative effect on HuH7, which expresses a higher level of RAGE. MK615 suppresses the proliferative effect of Glycer-AGE on HuH7 by decreasing the expression of RAGE.

Oxidative stress-associated rise of hepatic protein glycation increases inflammatory liver injury in uncoupling protein-2 deficient mice

Mitochondrial dysfunction seems to be intrinsically involved in the pathogenesis of multiple organ failure because of enhanced production of reactive oxygen species and induction of oxidative damage. Chronic oxidative stress in turn causes an accumulation of advanced glycation end products (AGEs). To investigate whether mitochondrial dysfunction-associated oxidative stress leads to increased formation and accumulation of AGE, we studied hepatic glycation in uncoupling protein-2 (UCP2-/-) knockout mice. Using the galactosamine/lipopolysaccharide (G/L)-induced liver injury model, we further tested the hypothesis that a mitochondrial dysfunction-associated increase of hepatic glycation is causative for increased liver injury. Under baseline conditions, UCP2-/- mice showed higher malondialdehyde levels and reduced glutathione/glutathione disulfide ratios as well as significantly higher hepatic levels of AGE and hepatic expression of receptor for AGE (RAGE) when compared with UCP2+/+ mice, indicative for increased oxidative stress and hepatic glycation. Further, livers of G/L-challenged UCP2-/- mice revealed significantly more pronounced tissue injury and were found to express higher levels of AGE and RAGE compared with wild-type mice. Functional blockade of RAGE by application of recombinant RAGE significantly diminished liver damage particularly in UCP2-/- mice. This in turn increased survival from 30% in UCP2+/+ mice to 50% in UCP2-/- mice. In summary, we show for the first time that mitochondrial dysfunction-associated oxidative stress enhances hepatic protein glycation, which aggravates inflammation-induced liver injury. Targeting the AGE/RAGE interaction by the blockade of RAGE might be of therapeutic value for the oxidative stress-exposed liver.

The receptor for advanced glycation end products (RAGE) sustains autophagy and limits apoptosis, promoting pancreatic tumor cell survival

Activation of the induced receptor for advanced glycation end products (RAGE) leads to initiation of NF-kappaB and MAP kinase signaling pathways, resulting in propagation and perpetuation of inflammation. RAGE-knockout animals are less susceptible to acute inflammation and carcinogen-induced tumor development. We have reported that most forms of tumor cell death result in release of the RAGE ligand, high-mobility group protein 1 (HMGB1). We now report a novel role for RAGE in the tumor cell response to stress. Targeted knockdown of RAGE in the tumor cell, leads to increased apoptosis, diminished autophagy and decreased tumor cell survival . In contrast, overexpression of RAGE is associated with enhanced autophagy, diminished apoptosis and greater tumor cell viability. RAGE limits apoptosis through a p53-dependent mitochondrial pathway. Moreover, RAGE-sustained autophagy is associated with decreased phosphorylation of mammalian target of rapamycin (mTOR) and increased Beclin-1/VPS34 autophagosome formation. These findings show that the inflammatory receptor, RAGE, has a heretofore unrecognized role in the tumor cell response to stress. Furthermore, these studies establish a direct link between inflammatory mediators in the tumor microenvironment and resistance to programmed cell death. Our data suggest that targeted inhibition of RAGE or its ligands may serve as novel targets to enhance current cancer therapies.

Fueling inflammation at tumor microenvironment: the role of multiligand/RAGE axis

The receptor for advanced glycation end products (RAGE), firstly described in 1992, is a single-transmembrane and multiligand member of the immunoglobulin protein family. RAGE engagement produces activation of multiple intracellular signaling mechanisms involved in several inflammation-associated clinical entities, such as diabetes, cancer, renal and heart failures, as well as neurodegenerative diseases. Although RAGE expression has been extensively reported in many cancer types, it is now emerging as a relevant element that can continuously fuel an inflammatory milieu at the tumor microenvironment, thus changing our perception of its contribution to cancer biology. In this review, we will discuss the role of multiligand/RAGE axis, particularly at the multicellular cross talk established in the inflammatory tumor microenvironment. A better understanding of its contribution may provide new targets for tumor management and risk assessment.

Expression of receptor for advanced glycation end products (RAGE) is related to prognosis in patients with esophageal squamous cell carcinoma

The receptor for advanced glycation end products (RAGE), known as a multiligand receptor for certain stress-associated factors, has been considered to affect the characteristic differences of various cancer cells. We analyzed the expression and clinicopathological significance of RAGE in esophageal squamous cell carcinoma. We investigated immunohistochemically the relationship between RAGE expression and clinicopathological factors, including prognosis, in surgical specimens of primary tumors in 216 patients with esophageal squamous cell carcinoma. Prognostic factors were examined by univariate and multivariate analyses (Cox proportional hazard regression model). The positive expression rate of RAGE was 50%. RAGE expression was negatively correlated with depth of invasion and venous invasion. Moreover, tumors with positive RAGE expression exhibited better prognosis than those with negative RAGE expression (5-year survival, 52% vs. 32%, respectively). Multivariate analysis indicated that the positive expression of RAGE was an independent prognostic factor, along with tumor depth and nodal metastasis. Our findings suggest that loss of RAGE expression may play an important role in the progression of esophageal squamous cell carcinoma. Evaluation of the expression of RAGE could be useful for determining the tumor properties, including those associated with prognosis, in patients with esophageal squamous cell carcinoma.