Nuclear actin-dependent Meg3 expression suppresses metabolic genes by affecting the chromatin architecture at sites of elevated H3K27 acetylation levels

Abstract

Nuclear actin mediates enhancer-dependent transcriptional regulation at compartment level, playing critical roles in 3D genome organization. In β-actin depleted cells, H3K27 acetylation is enhanced, directly affecting enhancer-dependent transcriptional regulation and gene expression changes during compartment-switching. Here, we report these mechanisms are influenced by the long non-coding RNA (lncRNA) Meg3. Bulk RNA-seq analysis and qPCR on wild-type (WT), heterozygous (HET), and β-actin knockout (KO) mouse embryonic fibroblasts (MEFs) show that β-actin depletion significantly alters expression of several lncRNAs, including Meg3. Results from ChIRP-seq, ChIRP-MS, and fRIP-qPCR revealed that in β-actin KO cells, Meg3 becomes enriched and binds to H3K27 acetylation marks within gene regulatory regions. By integrating RNA-seq, H3K27 acetylation ChIP-seq, ATAC-seq, and HiC-seq data through activity by contact (ABC) analysis, we discovered Meg3 binding disrupts promoter–enhancer interactions in β-actin KO cells. These results, combined with metabolomics in WT, HET, and β-actin KO MEFs, show Meg3 binding to regulatory regions at sites of increased H3K27 acetylation impairs the expression of genes involved in the synthesis of chondroitin, heparan, dermatan sulfate, and phospholipases. We propose that in β-actin KO cells Meg3 binds to H3K27 acetylation levels. This interferes with promoter–enhancer interactions, disrupts genome organization, and downregulates gene expression and key metabolic pathways.