Liu, Esther

AbstractTranscription networks and epigenetic mechanisms including DNA methylation, histone modifications, and noncoding RNAs control lineage commitment of multipotent mesenchymal progenitor cells. Proteins that read, write, and erase histone tail modifications curate and interpret the highly intricate histone code. Epigenetic reader proteins that recognize and bind histone marks provide a crucial link between histone modifications and their downstream biological effects. Here, we investigate the role of bromodomain‐containing (BRD) proteins, which recognize acetylated histones, during osteogenic differentiation. Using RNA‐sequencing (RNA‐seq) analysis, we screened for BRD proteins (n = 40) that are robustly expressed in MC3T3 osteoblasts. We focused functional follow‐up studies on Brd2 and Brd4 which are highly expressed in MC3T3 preosteoblasts and represent “bromodomain and extra terminal domain” (BET) proteins that are sensitive to pharmacological agents (BET inhibitors). We show that small interfering RNA depletion of Brd4 has stronger inhibitory effects on osteoblast differentiation than Brd2 loss as measured by osteoblast‐related gene expression, extracellular matrix deposition, and alkaline phosphatase activity. Similar effects on osteoblast differentiation are seen with the BET inhibitor +JQ1, and this effect is reversible upon its removal indicating that this small molecule has no lasting effects on the differentiation capacity of MC3T3 cells. Mechanistically, we find that Brd4 binds at known Runx2 binding sites in promoters of bone‐related genes. Collectively, these findings suggest that Brd4 is recruited to osteoblast‐specific genes and may cooperate with bone‐related transcription factors to promote osteoblast lineage commitment and maturation.

Abstract While it is known that nuclear factor κ-B (NF-κB) signaling within macrophages regulates expression of downstream targets that can mediate either pro- or antitumor functions, the mechanisms that define predominant characteristics are not well understood. As macrophages are present in the tumor microenvironment of diverse tumor types, their characteristics have the potential to either support or hinder tumor growth and metastatic spread. Therefore, a method to shift the balance of tumor associated macrophages from pro- to antitumor functions could potentially target tumor cells directly and also recruit and activate other immune cells, resulting in significant therapeutic benefit. Our studies are designed to gain an understanding of how to use modulation of NF-κB signaling as the “pinch point” to generate antitumor phenotypes and determine how to achieve this modulation in a patient. We are using immortalized bone marrow-derived macrophages or ex vivo tumor-associated macrophages in cell culture approaches and inducible transgenic mice in in vivo approaches to investigate the mechanisms by which NF-κB defines macrophage characteristics. Interactions with tumor cells are also being investigated using co-culture and murine models. Our data suggests that high levels of NFκ-B activity in macrophages induce both direct tumor cell killing and immune stimulating responses. We are testing two different translational approaches. The first is liposomal muramyl tripeptide ethanolamine that acts as an immune stimulant by increasing NF-κB activity in macrophages. The second is preferential delivery of siRNA against the inhibitor of NFκ-B (IκB-alpha) to tumor-associated macrophages using polymeric nanoparticles. We hope to better understand the mechanisms by which NFκ-B regulates macrophage functions to inform development of a novel macrophage-based immunotherapy that could be effective across a wide spectrum of solid tumors and metastatic disease. Citation Format: Esther Liu, Alyssa A. Hoover, Whitney R. Harris, Whitney Barham, Oleg Tikhomirov, Dineo Khabele, Zahra Mirafzahli, Todd D. Giorgio, Andrew J. Wilson, Fiona E. Yull. Modulation of NFκ-B signaling to optimize antitumor characteristics in macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4711.