A novel lncRNA ROPM-mediated lipid metabolism governs breast cancer stem cell properties

Background: Cancer Stem Cells (CSCs) are considered as the major cause to tumor initiation, recurrence, metastasis, and drug resistance, driving poor clinical outcomes in patients. Long noncoding RNAs (lncRNAs) have emerged as crucial regulators in Cancer development and progression. However, limited lncRNAs involved in CSCs have been reported.

Methods: The novel lncROPM (a regulator of phospholipid metabolism) in breast CSCs (BCSCs) was identified by microarray and validated by qRT-PCR in BCSCs from breast Cancer cells and tissues. The clinical significance of lncROPM was evaluated in two breast Cancer cohorts and TANRIC database (TCGA-BRCA, RNAseq data). Gain- and loss-of-function assays were performed to examine the role of lncROPM on BCSCs both in vitro and in vivo. The regulatory mechanism of lncROPM was investigated by bioinformatics, RNA FISH, RNA pull-down, luciferase reporter assay, and actinomycin D treatment. PLA2G16-mediated phospholipid metabolism was determined by UHPLC-QTOFMS system. Cells' chemosensitivity was assessed by CCK8 assay.

Results: LncROPM is highly expressed in BCSCs. The enhanced lncROPM exists in clinic breast tumors and other solid tumors and positively correlates with malignant grade/stage and poor prognosis in breast Cancer patients. Gain- and loss-of-function studies show that lncROPM is required for the maintenance of BCSCs properties both in vitro and in vivo. Mechanistically, lncROPM regulates PLA2G16 expression by directly binding to 3'-UTR of PLA2G16 to increase the mRNA stability. The increased PLA2G16 significantly promotes phospholipid metabolism and the production of free fatty acid, especially arachidonic acid in BCSCs, thereby activating PI3K/Akt, Wnt/β-catenin, and Hippo/YAP signaling, thus eventually involving in the maintenance of BCSCs stemness. Importantly, lncROPM and PLA2G16 notably contribute to BCSCs chemo-resistance. Administration of BCSCs using clinic therapeutic drugs such as doxorubicin, cisplatin, or tamoxifen combined with Giripladib (an inhibitor of cytoplasmic Phospholipase A2) can efficiently eliminate BCSCs and tumorigenesis.

Conclusions: Our study highlights that lncROPM and its target PLA2G16 play crucial roles in sustaining BCSC properties and may serve as a biomarker for BCSCs or other Cancer Stem Cells. Targeting lncROPM-PLA2G16 signaling axis may be a novel therapeutic strategy for patients with breast Cancer.