ORIGINAL ARTICLE HMGB1 enhances the protumoral activities of M2 macrophages by a RAGE-dependent mechanism Armando Rojas 1 & Fernando Delgado-López 1 & Ramón Perez-Castro 1 & Ileana Gonzalez 1 & Jacqueline Romero 1 & Israel Rojas 1 & Paulina Araya 1 & Carolina Añazco 1 & Erik Morales 2 & Jorge Llanos 3 Received: 2 July 2015 /Accepted: 17 August 2015 # International Society of Oncology and BioMarkers (ISOBM) 2015 Abstract 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 in- duced by Il-4/IL13 and promotes tumor cell growth and vas- cularization. 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 macro- phages. 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 macro- phages. MKN45 cells co-cultured with M2 macrophages treated with HMGB1 at different times displayed higher inva- sive abilities. Additionally, conditioned medium from HMGB1-treated M2 macrophages promotes angiogenesis in vitro. RAGE-targeting knockdown abrogates these activi- ties. Overall, the present findings suggest that HMGB1 may contribute, by a RAGE-dependent mechanism, to the protumoral activities of the M2 phenotype. Keywords Receptor for advanced glycation end-products (RAGE) . HMGB1 . Macrophage polarization . Tumor-associated macrophages Introduction Macrophages are a heterogeneous population of innate mye- loid cells and represent a major group of non-specific immune cells. They are originated from monocytic precursors in the blood and once infiltrated into tumor stroma may undergo a polarized activation process, thus rendering two distinct po- larization states: the classically activated type 1 macrophages (M1) and the alternative activated type 2 macrophages (M2). The classically activated M1 phenotype can be induced by bacterial products and interferon-γ (IFN-γ) and exerts a cyto- toxic effect on cancer cells. The alternatively activated M2 phenotype can be induced by Il-4/IL13 and promotes tumor cell growth and vascularization [1]. Tumor-associated macrophages (TAMs) constitute the pre- dominant component of leukocytic infiltrate in many malig- nancies including gastric tumors. TAMs are poorly cytotoxic against neoplastic cells and may actually favor tumor cell survival and proliferation [2]. Furthermore, it is known that TAMs acquire a specific phenotype (M2), oriented toward tumor growth, angiogenesis, and immune suppression [3, 4]. M2 polarization is promoted by signals presented at the tumor microenvironment such as PGE2, TGF-β, IL-6, and IL-10 which are produced by tumor cells and by TAMs them- selves. Thus, the M2 phenotype of TAMs is associated with profound effects on tumor progression [5–7]. The receptor of advanced glycation end-products (RAGE) has been described in several cancer types including gastric, prostate, lung, pancreas, and liver malignancies. In addition, a compelling body of evidence has shown the contribution of * Armando Rojas arojasr@ucm.cl 1 Biomedical Research Labs, Medicine Faculty, Catholic University of Maule, 3605 San Miguel Ave., Talca, Chile 2 Pathology Unit, Regional Hospital, Talca, Chile 3 Gastroenterology Unit, Regional Hospital, Talca, Chile Tumor Biol. DOI 10.1007/s13277-015-3940-y