Abstract
BACKGROUND: This study aimed to analyze the functional role of Brd4 in colorectal cancer (CRC) organoids. Brd4 was identified as a CRC-related gene by our previous Sleeping Beauty mutagenesis transposon screening in mice. Brd4 is a transcriptional regulator that recognizes acetylated histones and is known to be involved in inflammatory responses. The role of Brd4 in CRC development remains largely unknown. METHODS: We knocked out Brd4 in tumor organoids carrying mutations in Apc and Kras to generate Brd4KO organoids, and performed RNA-seq. The response of Brd4KO organoids to IFNγ was analyzed via a cell viability assay, an apoptosis assay, and RNAseq. The results were validated by pharmacological inhibition experiments with JQ1 in human CRC organoids. RESULTS: In Brd4KO organoids, the IFNγ signaling genes Il33 and Myc target genes were downregulated. The addition of IFNγ to the colon organoids induced apoptosis, but IFNγ-induced apoptosis was attenuated in the Brd4KO organoids compared with the control organoids (two-sided t-test, P < 0.05). Similar results were obtained from pharmacological inhibition with JQ1 in human CRC organoids; IL33 expression was decreased, and IFNγ-induced apoptosis was attenuated in the presence of JQ1. CONCLUSIONS: Our results showed that the inhibition of Brd4 suppressed IFNγ-induced cytotoxicity by modulating the Jak-Stat pathway. These data suggested that the inhibition of Brd4 could increase cell viability in the cancer microenvironment where IFNγ is abundant, revealing a new aspect of the molecular mechanism of CRC development. Our results may help in evaluating the application of Bet inhibitors in treating CRC. Additionally, our RNA-seq data sets will be helpful for clarifying the relationship between Brd4 and immunomodulators, such as Il33, or for studying the responses of colonic epithelial cells to IFNγ.