Stabilization of SQLE mRNA by WTAP/FTO/IGF2BP3-dependent manner in HGSOC: implications for metabolism, stemness, and progression

The metabolic reprogramming in high-grade serous ovarian carcinoma (HGSOC) affects the tumor stemness, which mediates tumor recurrence and progression. Knowledge of the stemness and metabolic characteristics of HGSOC is insufficient. Squalene epoxidase (SQLE), a key enzyme in cholesterol metabolism, was significantly upregulated in HGSOC samples with a fold change of about 4 in the RNA sequencing analysis. SQLE was positively related to peritoneal metastasis and poor prognosis of HGSOC patients. Functionally, SQLE drove cancer cell proliferation and inhibited apoptosis to accelerate HGSOC growth. SQLE was highly expressed in ALDH⁺CD133⁺ FACS-sorted cells derived from HGSOC cells and ovarian cancer stem cells (OCSCs)-enriched tumorspheres. SQLE overexpression resulted in enhanced CSC-like properties, including increased tumorsphere formation and stemness markers expression. In vivo, SQLE not only promoted cell line-derived xenografts growth but extended the OCSCs subpopulation of single-cell suspension. Moreover, non-targeted metabolomics profiling from UPLC-MS/MS system identified 90 differential metabolites responding to SQLE overexpression in HGSOC cells. Among them, the dysfunctional metabolisms of cholesterol and glutathione were involved in the maintenance of HGSOC stemness. Previous studies showed the alteration of N6-Methyladenosine (m6A) modification in HGSOC development. Herein, the m6A modification in the 3'UTR and CDS regions of SQLE mRNA was increased due to upregulated methyltransferases WTAP and downregulated demethylases FTO, which was recognized by m6A-binding proteins IGF2BP3, rather than IGF2BP1 or IGF2BP2, thereby stabilizing the SQLE mRNA. These results suggested that SQLE was a novel potential clinical marker for predicting the HGSOC development and prognosis, as well as a potential therapeutic target of HGSOC.