Abstract 2091: Macrophage PI3Kg control of chromatin accessibility and transcription factor activity promotes immune suppression and tumor progression
Authors: Chen Hui , Liao Jingwen , Flores Christina , Hargreaves Diana , Varner Judith 
Published: June 2022

Abstract
Tumor development and progression are associated with immune suppression and evasion as well as angiogenesis, fibrosis, and metastasis. Macrophages play critical roles in tumor progression by controlling these events and are the focus of efforts to develop novel cancer therapeutics. We previously showed that PI(3)Kinase γ, a class Ib phosphatidyl inositol 3, 4, 5 kinase that is expressed primarily in myeloid lineage cells, controls tumor progression by serving as a critical switch between immune stimulation and suppression. PI3Kγ also promotes angiogenesis, fibrosis and metastasis. PI3Kγ signaling in macrophages promotes transcription of tumor-promoting cytokines and factors such as Pdgf, Tgfb, Ccl2, Plau, Mmps and Arg-1 and inhibits expression of Il12, Tnfa, Nos2 and other pro-inflammatory factors to stimulate tumor progression and immune evasion. Genetic or pharmaceutical inhibition of PI3Kγ reverses these events and suppress tumor growth. In order to develop novel strategies to control macrophage contributions to cancer progression, we investigated in detail how this kinase controls gene expression. We found that PI3Kγ deletion or inhibition with a selective inhibitor IPI-549, which is currently in late stage clinical development for cancer therapy, stimulates the expression and secretion of IL12, IL6, IL1β, NOS, IFNα, and TNFα, while reducing the secretion and expression of IL10, CCL2, PDGFβ, ARG-1, TGFβ and other factors. Gene expression analysis indicates that PI3Kγ inhibition in macrophages rapidly stimulates transcription of NFκB and IFNγ driven pro-inflammatory pathways as well as nuclear translocation of transcription factors STAT1, IRF1, IRF3, TBK1 and NFκB and inhibition of CEBPβ nuclear activity. To further understand the impact of PI3Kγ on transcription in macrophages, we performed ATAC seq on WT and PI3Kγ null macrophages stimulated with LPS/IFNγ in order to determine the impact of PI3Kγ activity and inhibition on chromatin accessibility. We found that PI3Kγ deletion promoted more open chromatin sites for IRF, FRA I, Pu.1, and NFκB binding, as well as fewer open chromatin sites for AP1 (FOS/JUN), IRF8, and CEBP sites. Importantly, we identified overall chromatin accessibility in the promoters of some NFκB regulated genes, such as Tnfα and Il6, as well as novel open chromatin sites in the promoters for Il12b and Il1b in PI3Kγ null macrophages. We also identified novel closed chromatin sites in the promoters of Il10, Plau and Ccl2, genes that are downregulated upon PI3Kγ inhibition. Further studies to identify the mechanisms by which PI3Kγ regulates transcription are investigating PI3Kγ controls of epigenetic modifiers and transcription factors are ongoing. These studies should lead to the identification of new approaches to regulate tumor associated macrophages to inhibit tumor progression.
Citation Format: Hui Chen, Jingwen Liao, Christina Flores, Diana Hargreaves, Judith Varner. Macrophage PI3Kg control of chromatin accessibility and transcription factor activity promotes immune suppression and tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2091.