The long non-coding RNA MALAT1 modulates NR4A1 expression through a downstream regulatory element in specific cancer-cell-types

Abstract

Chromatin-associated long non-coding RNAs (lncRNAs) have been shown to define chromatin density, regulate gene expression, and are involved in the initiation and progression of various cancer types. Despite the wealth of studies describing transcriptome changes upon lncRNA modulation, little data is showing the direct effects of lncRNA on regulatory elements (REs) that drive gene expression. Here we explored the molecular mechanism of the chromatin-interacting lncRNA, MALAT1, through RNA- and ATAC-seq, using HeLa cells as a model system. Time-resolved MALAT1 knock-down assays revealed its direct regulation of a limited number of protein-coding genes. Loss of MALAT1 resulted in a substantial loss of chromatin accessibility downstream of the NR4A1 gene, associated with its down-regulation. CRISPR-i assays revealed that this region corresponds to a new downstream RE. Next, using TCGA data, we identified a direct correlation between the expression of NR4A1 and the accessibility of the downstream RE in breast cancer. The molecular mechanism was validated on estrogen receptor (ER) positive breast cancer cells (MCF7) and Pancreatic Duct Epithelioid Carcinoma (PANC1) cells, not showing this effect according to TCGA data. Indeed, MALAT1 regulates the expression of NR4A1 in a cell type-specific manner by changing the accessibility of the downstream RE. MALAT1 exhibits a molecular mechanism that fine-tunes the expression of cancer drivers, like NR4A1, in ER-positive breast cancer cells, but not in other cell types.