Serum deprivation response functions as a tumor suppressor gene in papillary thyroid cancer

The mechanism of papillary thyroid cancer (PTC) has shown numerous recurrently mutated genes, but the discovery of abnormal expression of novel tumor suppressor genes has been slow. The aim of our study is to explore the biological functions of SDPR in thyroid cancer. We reanalyzed the RNA-Seq data of PTC from The Cancer Genome Atlas (TCGA) database and found that serum deprivation response (SDPR) was significantly downregulated in PTC. Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) was performed to assess the expression of SDPR. Both loss- and gain-of-function experiments, and flow cytometry were performed to investigate the functions. SDPR was significantly downregulated in PTC. Reduced expression of SDPR was associated with larger tumor size, more serious lymph node metastasis, and advanced American Joint Committee on Cancer (AJCC) stage. Patients with lower SDPR expression had a shorter recurrence-free survival. SDPR expression and AJCC stage were independent predictors of poor recurrence-free survival (RFS). Moreover, cell proliferation, colony formation, and migration were inhibited after SDPR overexpression, whereas knockdown of SDPR exerted an oncogenic effect. SDPR induction also initiated the mesenchymal-epithelial transition, alongside suppressing AKT signaling and cyclin family expression. Apart from DNA methylation, LOC105373813, may also co-regulate SDPR expression by forming a stable hybrid with SDPR messenger RNA. Our study indicated that SDPR may function as a potential prognostic marker in PTC.