SOX1 Functions as a Tumor Suppressor by Repressing HES1 in Lung Cancer

SIMPLE SUMMARY: Lung cancer is the most common reason for cancer-related death, and patient survival is mainly dependent on tumor stage. The median overall survival of patients who are diagnosed with advanced/metastatic non-small-cell lung cancer (NSCLC) is still less than 3 years. The poor survival rates highlight the unmet need to elucidate the mechanism underlying lung cancer carcinogenesis to improve treatment responses and overall survival. The expression and function of SOX1 in the progression of lung cancer are still unclear. Through in vitro and in vivo experiments, we demonstrated that SOX1 repressed anchorage-independent growth, invasion, and metastasis. Interestingly, SOX1 performed its function by repressing hairy and enhancer of split 1 (HES1). Recent studies have shown that HES1, which is a helix–loop–helix transcription factor, performs important functions in stemness, metastasis, and drug resistance in cancer. These results suggest that SOX1 is a tumor suppressor that affects the carcinogenesis of lung cancer. ABSTRACT: The development of lung cancer is a complex process that involves many genetic and epigenetic changes. Sex-determining region Y (SRY)-box (SOX) genes encode a family of proteins that are involved in the regulation of embryonic development and cell fate determination. SOX1 is hypermethylated in human cancers. However, the role of SOX1 in the development of lung cancer is unclear. We used quantitative methylation-specific polymerase chain reaction (MSP), quantitative reverse transcription polymerase chain reaction (RT–PCR) analysis, and web tools to confirm the frequent epigenetic silencing of SOX1 in lung cancer. Stable overexpression of SOX1 repressed cell proliferation, anchorage-independent growth, and invasion in vitro as well as cancer growth and metastasis in a xenograft mouse model. Knockdown of SOX1 by the withdrawal of doxycycline partly restored the malignant phenotype of inducible SOX1-expressing NSCLC cells. Next, we discovered the potential downstream pathways of SOX1 using RNA-seq analysis and identified HES1 as a direct target of SOX1 using chromatin immunoprecipitation (ChIP)-PCR. Furthermore, we performed phenotypic rescue experiments to prove that overexpression of HES1-FLAG in SOX1-expressing H1299 cells partly reversed the tumor-suppressive effect. Taken together, these data demonstrated that SOX1 acts as a tumor suppressor by directly inhibiting HES1 during the development of NSCLC.