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Proteomic Characterization of human small airway epithelial cells (hSAECs) in the context of respiratory syncytial virus infection and BRD4 inhibition.

ABSTRACT: Bromodomain-containing Protein 4 (BRD4) is a transcriptional regulator associated with cancer biology, inflammation, and fibrosis. In airway viral infection, non-toxic BRD4-specific inhibitors (BRD4i) block the release of pro- inflammatory cytokines and prevent downstream remodeling. Although the chromatin modifying functions of BRD4 in inducible gene expression have been extensively investigated, its roles in post-transcriptional regulation are not as well understood. Based on its interaction with transcriptional elongation complex and spiceosome, we hypothesize that BRD4 is a functional regulator of RNA processing. To address this question, we combine data-independent analysis - parallel accumulation-serial fragmentation (diaPASEF) with RNA-sequencing to achieve deep coverage of the proteomic and transcriptomic landscape of human small airway epithelial cells exposed to viral challenge and treated with BRD4i. The transcript-level data was further interrogated for alternative splicing analysis, and the resulting data sets were correlated to identify pathways subject to post-transcriptional regulation. We discover that BRD4 regulates alternative splicing of key genes, including Interferon-related Developmental Regulator 1 (IFRD1) and X-Box Binding Protein 1 (XBP1), related to the innate immune response and the unfolded protein response, respectively. These findings extend the actions of BRD4 in control of post-transcriptional RNA processing.

INSTRUMENT(S): Bruker Daltonics timsTOF series

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Lung, Epithelial Cell

DISEASE(S): Respiratory Syncytial Virus Infectious Disease

SUBMITTER: Morgan Mann

LAB HEAD: Allan R. Brasier

PROVIDER: PXD039212 | Pride | 2023-06-13

REPOSITORIES: Pride

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Project description:The histone acetyl-reader BRD4 is an important regulator of chromatin structure and transcription, yet factors modulating its activity have remained elusive. Here we describe two complementary screens for genetic and physical interactors of BRD4, which converge on the folate pathway enzyme MTHFD1. We show that a fraction of MTHFD1 resides in the nucleus, where it is recruited to distinct genomic loci by direct interaction with BRD4. Inhibition of either BRD4 or MTHFD1 results in similar changes in nuclear metabolite composition and gene expression, and pharmacologic inhibitors of the two pathways synergize to impair cancer cell viability in vitro and in vivo. Our finding that MTHFD1 and other metabolic enzymes are chromatin-associated suggests a direct role for nuclear metabolism in the control of gene expression. BRD4 is an important chromatin regulator with roles in gene regulation, DNA damage, cell proliferation and cancer progression1-4. The protein is recruited to distinct genomic loci by the interaction of its tandem bromodomains with acetylated lysines on histones and other nuclear proteins5. There, BRD4 acts as a transcriptional activator by P-TEFb-mediated stimulation of transcriptional elongation6. The activating function of BRD4 on key driver oncogenes like MYC have made this epigenetic enzyme an important therapeutic target in both BRD4 translocated and BRD4 wild-type cancers3,7-12, and at least seven bromodomain inhibitors have reached the clinical stage13. Genome-wide studies have identified the role of BRD4-induced epigenetic heterogeneity in cancer cell resistance14, and factors defining BRD4 inhibitor response15,16. However, despite its clinical importance and the broad role of BRD4 in chromatin organization, surprisingly little is known about factors that are directly required for BRD4 function. To systematically expand the list of known BRD4 interactors5 and to characterize proteins directly required for BRD4 function, we developed a strategy of two complementary screens for genetic and physical partners of BRD4. The two approaches converge on a single factor, methylenetetrahydrofolate dehydrogenase 1 (MTHFD1). Our description of a transcriptional role for this C-1-tetrahydrofolate synthase highlights a direct connection between nuclear folate metabolism and cancer regulation.

Dataset Information

Proteomic Characterization of human small airway epithelial cells (hSAECs) in the context of respiratory syncytial virus infection and BRD4 inhibition.

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