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.