DNMT1-driven Methylation of RORA Facilitates Esophageal Squamous Cell Carcinoma Progression Under Hypoxia Through SLC2A3

Background: The RAR-related orphan receptor alpha (RORA), a circadian clock molecule, is highly associated with anti-oncogenes. In this paper, we defined the precise action and mechanistic basis of RORA in ESCC development under hypoxia.

Methods: Expression analysis was conducted by RT-qPCR, western blotting, immunofluorescence (IF), and immunohistochemistry (IHC) assays. The functions of RORA were assessed by detecting its regulatory effects on cell viability, motility, invasion, and tumor growth. DNA pull-down assay and proteomic analysis were employed to identify proteins bound to the RORA promoter. The promoter methylation level of RORA was detected by DNA pyrosequencing. RNA-seq analysis was performed to explore the downstream mechanisms of RORA, and the transcriptional regulation of RORA on SLC2A3 was verified by ChIP-qPCR and dual-luciferase reporter assay. Glycolysis was assessed by detecting the consumption of glucose and the production of lactic acid and ATP.

Results: In vitro, RORA was shown to suppress ESCC cell viability, motility, and invasion under hypoxic condition. In vivo, increased RORA expression in mouse xenografts impeded tumor growth. DNMT1 was identified to widely exist in the RORA promoter, increasing DNA methylation and reducing RORA expression in hypoxia-induced KYSE150 ESCC cells. Mechanistically, RORA was found to inactivate the transcription of glucose transporter protein SLC2A3 by interacting with its promoter F1 region. Furthermore, rescue experiments revealed that RORA-mediated suppressive effects on ESCC cell migration and invasion were largely based on its negative regulation of SLC2A3 and glycolysis.

Conclusion: DNMT1-driven methylation of RORA promotes ESCC progression largely through affecting SLC2A3 transcription and glycolysis. These findings turn RORA into potential target of anti-cancer therapeutic agents.