NNK-mediated upregulation of DEPDC1 stimulates the progression of oral squamous cell carcinoma by inhibiting CYP27B1 expression

Oral squamous cell carcinoma (OSCC) is a prevalent and malignant cancer. However, the molecular mechanism of OSCC progression is not fully understood. In this study, we observed that the DEP domain containing 1 (DEPDC1) protein was overexpressed in OSCC tissues and that the increased expression of DEPDC1 was closely associated with tumor size and poor clinical outcomes in OSCC patients. The results of functional investigations demonstrated that DEPDC1 stimulates OSCC cell proliferation by inhibiting cytochrome P450 family 27 subfamily B member (CYP27B1) expression. Furthermore, we observed that upregulated DEPDC1 expression was closely associated with smoking status in OSCC patients. The results of in vitro experiments showed that the tobacco compound 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) stimulates DEPDC1 expression by promoting the methylation of its gene body by increasing DNMT1 expression in OSCC cells. Notably, the silencing of DEPDC1 dramatically inhibited OSCC growth by inhibiting cell proliferation and inducing apoptosis in vivo. These findings suggest that smoking causes DEPDC1 overexpression in OSCC through DNMT1-regulated DNA methylation and that upregulated DEPDC1 stimulates OSCC cell proliferation by inhibiting CYP27B1 expression. Our results establish a new mechanism of OSCC progression and highlight DEPDC1 as a candidate prognostic biomarker and therapeutic target in OSCC.