Silencing SHMT2 Inhibits the Progression of Oral Squamous Cell Carcinoma Through Cell Cycle Regulation

Abstract

Background Serine hydroxymethyltransferase 2 (SHMT2) is a vital metabolic enzyme, which catalyzes the conversion of serine to glycine in one-carbon metabolism. SHMT2 has been reported to play a crucial role in the progression of tumors, but its function in oral squamous cell carcinoma (OSCC) remains unclear.Method SHMT2 expression was analyzed using publicly-available online databases, and assessed using immunohistochemistry staining of collected clinical specimens. The correlation between SHMT2 expression and the cell cycle was predicted through bioinformatic analysis, including weighted gene co-expression network analysis and gene set enrichment analysis. After transfection with siRNA CCK8 assay, Edu staining, flow cytometry, transwell, and wound healing experiments were performed to verify the functional role of SHMT2 in vitro. A stable cell line with SHMT2 silencing was established to detect the oncogenic function of SHMT2 in vivo.Results We found that SHMT2 was up-regulated in OSCC tissues and cell lines, and high level of SHMT2 was significantly linked with a poorer clinical outcome for OSCC patients. Bioinformatic analysis found that SHMT2 was closely related with cell cycle regulation. Down-regulation of SHMT2 effectively suppressed the proliferation rate of OSCC cells, and induced the prolongation of the G1 phase of the cell cycle in vitro. Western blotting found that cell cycle-related regulators such as cyclin-dependent kinase 4 (CDK4) and cyclinD1 expression levels were increased, while the expression levels of the cyclin-dependent kinase inhibitors p21Cip1 and p27Kip1 were decreased after SHMT2 knockdown. Invasive and migrative ability and epithelial mesenchymal transition were impaired by SHMT2 knockdown. Silencing SHMT2 in the HN6 cell line using short hairpin RNA impeded tumor growth in vivo.Conclusion Our findings suggested that high expression of SHMT2 in OSCC indicated low survival rates, and was associated with malignant behaviors of OSCC. SHMT2 may serve as a novel prognostic and therapeutic target of interest in OSCC.