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Epigenomic preconditioning of peripheral monocytes determines their transcriptional response to the tumor microenvironment

ABSTRACT: Monocytes are recruited to tumors and undergo transcriptional reprogramming resulting in tumor-promoting functions. Epigenomic features, such as post-translational modification of histones and chromatin accessibility, are key determinants of transcription factor binding and thereby play an important role in determining transcriptional responses to the tissue environment. It remains unknown whether systemic tumor-associated signals could alter the epigenomic landscape of peripheral monocytes before they reach the tumor, thus shaping their subsequent response to the tumor microenvironment. Here, we performed genome-wide analyses of multiple histone modifications (H3K4me1, H3K4me3, H3K27ac) and chromatin accessibility in a mouse model and found that the distal tumor caused extensive remodeling of both H3K4me3+ promoters and H3K4me1+ enhancers in peripheral monocytes. Specifically, this involved the repression of interferon-responsive regulatory elements as well as the stablishment of enhancers harboring binding motifs for transcription factor families downstream of pro-inflammatory signaling, such as C/EBP, AP-1 and STAT. Reprogrammed enhancers in peripheral monocytes could be linked to sustained gene expression changes that persisted after tumor infiltration. In addition, key pro-tumor genes upregulated in tumor-infiltrating monocytes showed epigenetic priming already in the circulation. Overall, these results indicate that the epigenomic landscape of peripheral monocytes is altered in response to a distal tumor, and this can shape the transcriptional response of monocytes to the tumor microenvironment.

ORGANISM(S): Mus musculus

PROVIDER: GSE268992 | GEO | 2025/06/25

REPOSITORIES: GEO

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Project description:FOXA1 is a pioneer factor that is important in hormone dependent cancer cells to stabilise nuclear receptors, such as estrogen receptor (ER) to chromatin. FOXA1 binds to enhancers regions that are enriched in H3K4mono- and dimethylation (H3K4me1, H3K4me2) histone marks and evidence suggests that these marks are requisite events for FOXA1 to associate with enhancers to initate subsequent gene expression events. However, exogenous expression of FOXA1 has been shown to induce H3K4me1 and H3K4me2 signal at enhancer elements and the order of events and the functional importance of these events is not clear. We performed a FOXA1 Rapid Immunoprecipitation Mass Spectrometry of Endogenous Proteins (RIME) screen in ERα-positive MCF-7 breast cancer cells in order to identify FOXA1 interacting partners and we found histone-lysine N-methyltransferase (MLL3) as the top FOXA1 interacting protein. MLL3 is typically thought to induce H3K4me3 at promoter regions, but recent findings suggest it may contribute to H3K4me1 deposition, in line with our observation that MLL3 associates with an enhancer specific protein. We performed MLL3 ChIP-seq in breast cancer cells and unexpectedly found that MLL3 binds mostly at non-promoter regions enhancers, in contrast to the prevailing hypothesis. MLL3 was shown to occupy regions marked by FOXA1 occupancy and as expected, H3K4me1 and H3K4me2. MLL3 binding was dependent on FOXA1, indicating that FOXA1 recruits MLL3 to chromatin. Motif analysis and subsequent genomic mapping revealed a role for Grainy head like protein-2 (GRHL2) which was shown to co-occupy regions of the chromatin with MLL3. Regions occupied by all three factors, namely FOXA1, MLL3 and GRHL2, were most enriched in H3K4me1. MLL3 silencing decreased H3K4me1 at enhancer elements, but had no appreciable impact on H3K4me3 at enhancer elements. We identify a complex relationship between FOXA1, MLL3 and H3K4me1 at enhancers in breast cancer and propose a mechanism whereby the pioneer factor FOXA1 can interact with a chromatin modifier MLL3, recruiting it to chromatin to facilitate the deposition of H3K4me1 histone marks, subsequently demarcating active enhancer elements.

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Epigenomic preconditioning of peripheral monocytes determines their transcriptional response to the tumor microenvironment

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