Abstract LB-483: p53-dependent release of Alarmin HMGB1 is a central mediator of senescent phenotypes

Abstract

Abstract Cellular senescence irreversibly arrests the proliferation of cells at risk for malignant transformation in part through activities of the transcriptional regulator and tumor suppressor p53. Cells that senesce owing to DNA damage also secrete many biologically active factors, including inflammatory cytokines such as IL-6. The High Mobility Group Box 1 (HMGB1) protein is unusual in having two distinct functions. Intracellularly, it binds chromatin and modulates transcription, including stimulating p53 activity. In addition, necrosis or microbial infection causes HMGB1 leakage or active secretion, respectively, whereupon it functions as an extracellular Alarmin to signal tissue damage and promote tissue regeneration, stem cell recruitment and immune activation. We show that HMGB1 is largely nuclear in non-senescent human and mouse fibroblasts and epithelial cells, but is actively exported from the nucleus and secreted by senescent cells. In culture and in vivo, HMGB1 re-localization occurred prior to the appearance of other hallmarks of senescence, and depended on the function of p53, but not the upstream p53 activator ATM. Old mice contained significantly higher levels of HMGB1 in serum compared to young animals. Disruption of HMGB1 stoichiometry, either by overexpression or depletion, induced a p53-dependent senescence growth arrest, but only HMGB1 overexpression, not HMGB1 depletion, promoted IL-6 secretion. Senescence-associated secretion required endogenous and secreted HMGB1 because deletion of endogenous HMGB1 – or addition of an HMGB1 blocking antibody - attenuated IL-6 secretion. Recombinant HMGB1 protein induced IL-6 secretion in cells depleted, but not harboring, endogenous HMGB1. Depletion of endogenous HMGB1 promoted NF-κ B transcriptional activity in cells cultured with recombinant HMGB1. Our findings identify a novel biological setting (senescence), independent of necrosis or microbial infection, in which HMGB1 secretion occurs, and link senescence-dependent HMGB1 redistribution to p53 activity and inflammatory cytokine secretion. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-483. doi:1538-7445.AM2012-LB-483