LncRNA NRAD1 regulates the triple-negative breast cancer transcriptome by miRNA biogenesis, localization, and predominately non-ceRNA interactions.

Breast cancer is a leading cause of cancer mortality in women with triple-negative breast cancer (TNBC) presenting greater treatment challenges due to its aggressive disease progression. Understanding TNBC's unique cell signaling and gene expression profiles will reveal novel therapeutic strategies. Non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have emerged as key regulators of gene expression and potential therapeutic targets. This study focuses on a TNBC-enriched lncRNA, non-coding RNA in the aldehyde dehydrogenase 1A pathway (NRAD1, previously LINC00284), which promotes progression in multiple cancers. Our analysis reveals that NRAD1 is central to miRNA-mRNA networks in TNBC cells, mediating cancer-promoting gene expression changes. Fractionation studies showed that NRAD1 is primarily located in the nucleus and mitochondria, with some cytoplasmic presence allowing for transcript-specific competitive endogenous RNA (ceRNA) interactions with miRNAs. However, NRAD1 primarily effects miRNAs independently of ceRNA activity, instead upregulating DICER (a miRNA biogenesis protein), altering sub-cellular distribution, and reducing biogenesis of mitochondria-localized miRNA (i.e., miR-4485-3p). These findings demonstrate novel regulatory interactions between the cancer-promoting lncRNA NRAD1 and miRNAs that alter gene expression in TNBC, expanding our understanding of regulatory lncRNA-miRNA effects, TNBC biology, and highlighting future therapeutic strategies for targeting non-coding RNAs.