Ileana Gonzalez

The receptor for advanced glycation end-products: A complex signaling scenario for a promiscuous receptor

Firstly described in 1992, the receptor for advanced glycation end-products has attracted increasing attention due to its diverse ligand repertoire and involvement in several pathophysiological processes associated with inflammation such as in diabetes, cancer, autoimmune diseases and neurodegenerative diseases. This receptor in addition to its binding capacity for advanced glycation end-products also recognizes some molecules classified as both, pathogen- and damage-associated molecular patterns and thus triggering the transcription of genes encoding inflammatory mediators. Some of these ligands are common for both, the receptor of advanced glycation end-products and members of the Toll-like receptor family, generating shared signaling cascades. Furthermore, these receptors may cooperate as essential partners through the recruitment and assembly of homo- and hetero-oligomers in order to strengthen the inflammatory response. The purpose of this review is to highlight the importance of some particular features of this multiligand receptor, its signaling cascade as well as the cross-talk with some members of the Toll-like receptor family.

The immunobiology of the receptor of advanced glycation end-products: Trends and challenges

Pattern-recognition receptors have been highly conserved in evolution. They recognize danger signals including both pathogen- and damage-associated molecular patterns, also known as alarmins. Several signaling pathways leading to an inflammatory reaction as part of an effective defensive response, are thus triggered. RAGE, a receptor initially considered for advanced glycation end-products, is also known to be activated by several danger signals, thus functioning as a pattern-recognition receptor. As a new member of this family, attempts to unraveling its functioning show that RAGE activation not only results in innate immune response but also contributes to promote and shape the acquired immune reaction. As reported for other members of the family, RAGE presents many polymorphic variants and additional studies are needed to elucidate its significance in immune response and disease susceptibility. Here we describe recent advances unraveling RAGE functions, as well as its significance and challenges in immunobiology.

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.

Cell line cross-contamination in biomedical research: a call to prevent unawareness

AbstractDuring the 1950s, cross-contamination of cell lines emerged as a problem with serious consequences on the quality of biomedical research. Unfortunately, this situation has worsened over years. In this context, some actions should be urgently undertaken to avoid the generation of misleading data due to the increasingly and sometimes neglected use of cross-contaminated cell lines. Unawareness about this problem may then turn many scientists into victims or even perpetrators of this unwanted situation. Collaborative actions involving researchers, cell banks, journals, and funding agencies are needed to save the scientific reputation as well as many public or private resources that are used to produce misleading data.

HMGB1 enhances the protumoral activities of M2 macrophages by a RAGE-dependent mechanism

The monocyte-macrophage lineage shows a high degree of diversity and plasticity. Once they infiltrate tissues, they may acquire two main functional phenotypes, being known as the classically activated type 1 macrophages (M1) and the alternative activated type 2 macrophages (M2). The M1 phenotype can be induced by bacterial products and interferon-γ and exerts a cytotoxic effect on cancer cells. Conversely, the alternatively activated M2 phenotype is induced by Il-4/IL13 and promotes tumor cell growth and vascularization. Although receptor for advanced glycation end-products (RAGE) engagement in M1 macrophages has been reported by several groups to promote inflammation, nothing is known about the functionality of RAGE in M2 macrophages. In the current study, we demonstrate that RAGE is equally expressed in both macrophage phenotypes and that RAGE activation by high-mobility group protein box1 (HMGB1) promotes protumoral activities of M2 macrophages. MKN45 cells co-cultured with M2 macrophages treated with HMGB1 at different times displayed higher invasive abilities. Additionally, conditioned medium from HMGB1-treated M2 macrophages promotes angiogenesis in vitro. RAGE-targeting knockdown abrogates these activities. Overall, the present findings suggest that HMGB1 may contribute, by a RAGE-dependent mechanism, to the protumoral activities of the M2 phenotype.

The emerging role of the receptor for advanced glycation end products on innate immunity.

Cells from innate immune system are activated by the engagement of germ-line encoded pattern-recognition receptors (PRRs) in response to the microbial insult. These receptors are able to recognize either the presence of highly conserved microbial components called pathogen-associated molecular patterns or endogenous danger-associated molecular patterns. These danger signals are recognized by different types of (PRRs), including the receptor for advanced glycation end products. This new PRR share both ligands and intracellular signaling with Toll-like receptors and thus may cooperate with each other as essential partners to strength inflammatory response. This review summarizes recent advances in understanding the promiscuity of this receptor as well as its role in the context of innate immunity by triggering an inflammatory response when innate immune cells detect infection or tissue injury.

Evidence of involvement of the receptor for advanced glycation end-products (RAGE) in the adhesion of Helicobacter pylori to gastric epithelial cells.

The adherence of Helicobacter pylori to gastric epithelial cells is required for prolonged persistence in the stomach and for induction of injury. Here, we first reported a new role of the receptor for advanced glycation end-products (RAGE) on the adherence of H. pylori to gastric epithelial cells, assessed by different methods and binding to immobilized RAGE. RAGE-targeted knock-down in MKN74 cell line markedly reduced not only the adhesion of H. pylori, but also the levels of IL-8 transcripts and protein released in response to infection. These data suggest that RAGE may represent a new factor on the pathogenesis of H. pylori infection.

High prevalence of virulence-associated genotypes in Helicobacter pylori clinical isolates in the Region del Maule, Chile.

Abstract The prevalence of Helicobacter pylori infection and the gastric cancer mortality rate in Chile are remarkably high. This study identified some virulence-associated genes in 78 H. pylori clinical isolates from dyspeptic patients from the Region del Maule, which is the region with the higher gastric cancer mortality rate in the country. The cagA, vacA and babA2 genes were detected in 94.9%, 100% and 97.4%, respectively. Two or more EPIYA C motifs were presented in 48.6% of cagA-positive strains, and this was associated with more severe histopathological findings in the gastric mucosa.

Tumor-associated macrophages in gastric cancer: more than bystanders in tumor microenvironment

Two very interesting articles recently published in Gastric Cancer [1, 2] added new light to the relevance of tumorassociated macrophages, not only for tumor biology but also for the prognosis of gastric cancer patients. The results published by Zhang et al. [1] demonstrate the prognostic significance of polarized tumor-associated macrophages (TAMs) for gastric cancer patients, and when combined with the TNM staging system may provide a useful tool for prognosis. Additionally, Yamaguchi et al. [2] reported that intraperitoneal TAMs of gastric cancer patients with peritoneal dissemination were polarized to the M2 phenotype, thus contributing to tumor progression. Macrophages are a crucial switch in the tuning machinery of inflammatory and host immune response, and they are present in most, if not all, solid tumors. Both clinical and experimental evidence suggest that TAMs have emerged as a critical regulatory cell type in the tumor microenvironment, supporting tumor growth and metastasis. In analogy to the dichotomic states used to initially classify mouse T-helper cells into Th1 and Th2 phenotypes, macrophages are known to undergo a polarization process resulting in two extreme phenotypes, the M1, or ‘‘classically activated,’’ macrophages, and the M2, or ‘‘alternatively activated,’’ macrophages. TAMs display several characteristics of the M2 phenotype, which, by contrast to M1, are associated with immunosuppression, promotion of tumor growth, angiogenesis, and metastasis [3, 4]. Data recently published by our group [5] are consistent with the general conclusions stated in both articles. Our data showed how the alarmin HMGB1, highly abundant in the tumor microenvironment and particularly relevant for gastric cancer [6], enhances the protumoral activities of M2 macrophages, promoting the invasiveness capacity of cocultured MKN-45 gastric cancer cells and increasing the production of both metalloproteinase-9 and mucin-1 in these tumor cells. Additionally, culture supernatants of HMGB1-stimulated M2 macrophages increased the formation of new blood vessels. All these activities are mediated by a mechanism dependent on the expression of the receptor for advanced glycation end products (RAGE), as RAGE targeting knockdown abrogated all these activities. Of note, Murray et al. [7] have recently highlighted that M1 and M2 polarized phenotypes represent only two extreme phenotypes in macrophage heterogeneity spectrum, and therefore it is imperative to unify experimental standards for diverse experimental scenarios. Although the results obtained by Yamaguchi and our own findings have some limitations because both were attained using the biased two extreme phenotypes (M1 and M2) approach, the significance of TAMs in gastric cancer should be equally considered. For many years, many attempts to correlate tumor-associated macrophages and prognosis have failed. Most of these studies have considered the intratumoral macrophage population as a whole, without any distinction of the relative abundance of macrophage/phenotype populations. However, these new data, independently published, clearly support that we must consider TAMs as very active This comment refers to the article available at doi:10.1007/s10120-015-0488-x.

Abstract 725: HMGB1-mediated RAGE activation mechanism in M2 macrophages

Tumor-associated macrophages display M2 phenotype and promote immunosuppression, tumor growth, angiogenesis and metastasis. We have previously reported that M2 macrophages express the receptor of advanced glycation end-products (RAGE) and their protumoral activities enhanced by HMGB1, a RAGE ligand highly abundant at the cancer microenvironment. However, RAGE is highly expressed by M1 macrophages and it is unknown if proinflammatory and antitumor cytotoxicity of M1 macrophages become skewed from classical antitumor activities to a tumor permissive profile when M2 macrophages are induced by HMGB1. In order to clarify whether RAGE contributes to inflammatory response inhibition in M2 macrophages, we look at some microRNAs, a tolerance-like state as well as to some epigenetic changes. Polarized M1 and M2 macrophages were derived from wild-type and RAGE-targeted knock-down THP-1 cells and treated with HMGB1 at different times. NFkB activation was assessed by p65, IKBalpha western blots, and p50 and p65 Transcription Factor Assay. Additionally, we analyzed changes of chromatin activity related to HMGB1 treatment by quantitative chromatin immunoprecipitation (ChIP) with antibodies against acetylated or methylated histone H3 at the IL-10 promoter. We showed that RAGE activation by HMGB1 did not produce NFkB activation, as assessed by either IKB alpha and phospho p65 western blots or by p65 and p50 trascription factor assays. In addition, HMGB1 did not modify M2 macrophage expression profile of relevant microRNAs for macrophage polarization such as miR-155, miR-21 and miR-125b. However, ChIP analysis showed that HMGB1 induced a transcription-prone histone modification at the IL-10 promoter in M2 macrophages and this epigenetic imprinting correlated with HMGB1-induced IL-10 production, leading to immunosupression. These results demonstrate that RAGE activation on M2 macrophages did not induce NFkB activation and suggest that epigenetic changes are a major mechanism by which activities described for M1 macrophages upon RAGE activation have become skewed during macrophage polarization. Citation Format: Armando Rojas, Paulina Araya, Jacqueline Romero, Fernando Delgado-Lopez, Ramon Perez-Castro, Ileana Gonzalez, Carolina Anazco, Erik Morales, Jorge Llanos, Fernando Vidal-Vanaclocha. HMGB1-mediated RAGE activation mechanism in M2 macrophages. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 725.