Long non-coding RNA NORAD inhibition upregulates microRNA-323a-3p to suppress tumorigenesis and development of breast cancer through the PUM1/eIF2 axis.

Long non-coding RNAs (lncRNAs) are known to competitively bind with microRNAs (miRNAs) to participate in human cancers. We aim to explore the role of non-coding RNA activated by DNA damage (NORAD) binding to miR-323a-3p in breast cancer (BC) with the involvement of pumilio RNA-binding family member 1 (PUM1)/eukaryotic initiation factor 2 (eIF2) axis. Expression of NORAD, miR-323a-3p and PUM1 in tissues and cell lines was detected, and the correlation between NORAD expression and clinicopathological features of BC patients was analyzed. The screened cell line was respectively transfected with altered NORAD or miR-323a-3p to reveal their roles in viability, migration, invasion and apoptosis of BC cells in vitro. The tumor growth in vivo was observed in nude mice. The binding relationships among NORAD, miR-323a-3p and PUM1 were analyzed, and the regulatory role of NORAD and miR-323a-3p in the eIF2 signaling pathway was assessed. NORAD and PUM1 were upregulated and miR-323a-3p was downregulated in BC. High NORAD expression indicated a poor prognosis of BC patients. NORAD inhibition or miR-323a-3p elevation inhibited malignant behaviors of BC cells. The in vivo assay revealed that NORAD inhibition or miR-323a-3p elevation inhibited tumor growth as well. MiR-323a-3p inhibition reversed the role of NORAD knockdown in the biological functions of BC cells while silencing PUM1 reversed the influence of NORAD overexpression on BC cells. NORAD bound with miR-323a-3p and miR-323a-3p targeted PUM1. NORAD and miR-323a-3p functioned through the PUM1/eIF2 axis. NORAD inhibition or miR-323a-3p elevation suppresses the development of BC through the PUM1/eIF2 axis.