Methylation-Mediated Silencing of ATF3 Promotes Thyroid Cancer Progression by Regulating Prognostic Genes in the MAPK and PI3K/AKT Pathways

Background: Aberrant expression of oncogenes and/or tumor suppressor genes (TSGs) drives the tumorigenesis and development of thyroid cancer. We investigated the expression and function of a member of the activating transcription factor (ATF)/cAMP-responsive element-binding protein (CREB) transcription factor (TF) family, ATF3, in thyroid cancer. Methods: Data from 80 patients with papillary thyroid cancer (PTC) in the First Affiliated Hospital of Sun Yat-sen University and 510 PTC samples in The Cancer Genome Atlas thyroid cancer database were utilized for gene expression and prognosis analyses. The survival data were analyzed by Kaplan–Meier curves and Cox regression with adjustment for age, sex, multilocality, extrathyroidal extension, lymph metastases, and history of neoadjuvant treatment. DNA methylation was analyzed by methylation-specific polymerase chain reaction (PCR) and bisulfite sequencing PCR. TFs binding to ATF3 promoter were identified by DNA pull-down combined with mass spectrum assay, and confirmed by quantitative PCR (qPCR), luciferase reporter assay, and chromatin immunoprecipitation (ChIP)-qPCR. We conducted functional assays in vitro and in a xenograft mouse model to evaluate the function of ATF3 in thyroid cancer. Integrated analyses based on RNA sequencing, ChIP-seq, and CUT&Tag assays were performed to explore the mechanisms underlying the function of ATF3. Results: ATF3 was significantly downregulated in PTC and patients with low ATF3 expression had reduced progression-free survival (adjusted hazard ratio = 0.50 [CI 0.26–0.98], p = 0.043). DNA hypermethylation in ATF3 promoter disrupted the binding of SP1 and MYC-MAX, leading to inactivation of the gene. ATF3 functioned as a TSG by inhibiting the proliferation and mobility of thyroid cancer cells. And ATF3 regulated the expression of a number of genes by binding to the regulatory elements of them, particularly for genes in MAPK and PI3K/AKT pathways. Among these target genes, filamin C was positively regulated by ATF3 and associated with a more favorable thyroid cancer prognosis, while dual specificity phosphatase 10, fibronectin-1, tenascin C, and CREB5 were negatively regulated by ATF3 and associated with a poorer prognosis. Conclusions: We observed that the promoter DNA hypermethylation decreased the expression of ATF3, which in turn promoted the progression of thyroid cancer, at least partially, by directly regulating prognosis-related genes in the MAPK and PI3K/AKT pathways.