SQLE promotes osteosarcoma progression via activating TGFβ/SMAD signaling pathway

Abstract The prognosis of advanced osteosarcoma (OS) has remained stagnant in last decades, requiring the identification of novel therapeutic targets. Recently, much attention was paid to the role of squalene epoxidase (SQLE), a rate-limiting enzyme in cholesterol metabolism, in the field of oncology. Here, we found the upregulation of SQLE in OS samples than that in normal tissues through data mining of public resources. A notable rise in SQLE protein levels in OS cells in comparison to human osteoblast cells was confirmed by western blot assay. Survival analysis showed that individuals with high SQLE expression had a lower median overall survival time compared to those with low SQLE expression. Univariate and multivariate Cox regression analyses showed that SQLE might have the potency to serve as an independently prognostic biomarker in OS. Loss- and gain-of-function experiments indicated that silence of SQLE suppressed OS cell proliferation, migration, and invasion, while overexpression of SQLE exerted the opposite effects. Mechanistically, TGF-β signaling pathway was identified as the downstream pathway of SQLE through bioinformatic methods, and the results of western blot assay showed that SQLE positively regulated the activity of TGFβ1/SMAD2/3 signaling in OS. Resue experiments demonstrated that SB431542, a small molecule that inhibits TGFβ/SMAD signaling, could partly reverse the promoting effects of SQLE on OS cell proliferation, migration, and invasion. Together, our results provided preliminary evidences that SQLE was a tumor-promoting factor and prognosis predictor in OS. SQLE promoted OS cell proliferation, migration, and invasion via activating TGFβ/SMAD signaling and targeting SQLE might be a potential strategy for the treatment of OS.