HDAC3-dependent transcriptional repression of FOXA2 regulates FTO/m6A/MYC signaling to contribute to the development of gastric cancer

As one of the deadliest malignancies, gastric cancer (GC) is often accompanied by a low 5-year survival following initial diagnosis, which accounts for a substantial proportion of cancer-related deaths each year worldwide. Altered epigenetic modifications of cancer oncogenes and tumor suppressor genes emerge as novel mechanisms have been implicated the pathogenesis of GC. In the current study, we aim to elucidate whether histone deacetylase 3 (HDAC3) exerts oncogenic role in GC, and investigate the possible mechanism. Initially, we collected 64 paired cancerous and noncancerous tissues surgically resected from GC patients. Positive expression of HDAC3, FTO, and MYC in the tissues was measured using Immunohistochemistry. Meanwhile, GC cell line BGC-823/AGS was selected and treated with lentivirus vectors for alteration of HDAC3, FTO, or FOXA2 expressions, followed by detection on mRNA and protein levels of HDAC3, FOXA2, FTO, and MYC using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blot assays. The results demonstrated that the expressions of HDAC3, FTO and MYC were upregulated, while FOXA2 expression was downregulated in GC tissues and cells. After that, the cell viability, migration, and invasion of GC cells were assessed by CCK-8 and Transwell assays, revealing that HDAC3 accelerated GC cell viability, migration and invasion by degrading FOXA2. Subsequently, the binding relationship among HDAC3, FOXA2, FTO, and MYC was assessed by assays of immunoprecipitation, dual-luciferase reporter gene, and chromatin immunoprecipitation assay. Methylation of m6A mRNA in GC cells was detected via gene-specific m6A qPCR and dot-blot assays. The transcription factor FOXA2 was found to bind to the FTO gene promoter and decreased its expression, while FTO stabilized MYC mRNA by reducing m6A methylation of MYC in GC cells. In addition, HDAC3 was observed to maintain the FTO/m6A/MYC signaling and regulated GC progression, which was also supported by in vivo animal study data of GC cell tumorigenesis in nude mice. These key observations uncover the tumor-initiating activities of HDAC3 in GC through its regulation on FOXA2-mediated FTO/m6A/MYC axis, highlighting the potential of therapeutically targeting epigenetic modifications to combat GC.