Serum starvation-induces down-regulation of Bcl-2/Bax confers apoptosis in tongue coating-related cells in vitro

Tongue squamous epithelial cells are the main component of tongue coating, with proliferation, differentiation and apoptosis being the root cause of the formation and maintenance of tongue coating. The present study aimed to explore the molecular mechanism by which serum influences tongue coating, to enable a better understanding for future investigations. Tongue carcinoma squamous cells were exposed to serum‑starvation in vitro. Cellular proliferation and apoptosis were observed by using 3‑[4,5‑dimethyl‑2‑thiazolyl]‑2,5‑diphenyl‑2‑H‑tetrazolium bromide (MTT) assay, flow cytometry, Hoechst staining, scanning electron microscope (SEM), transmission electron microscope (TEM), and by measuring the expression ratio of B‑cell lymphoma 2 apoptosis regulator (Bcl‑2)/Bcl‑2 associated protein X apoptosis regulator (Bax) mRNA and protein by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting, respectively. MTT assays revealed that serum‑starvation results in suppression of cellular proliferation, while flow cytometry data revealed that serum‑starvation induces cell cycle arrest at G1 phase and increases apoptosis. In addition, chromatin condensation and membrane blebbing were observed through Hoechst staining, TEM and SEM. The Bcl‑2/Bax ratio was found to be significantly decreased in cells that had undergone serum‑starvation by both RT‑qPCR and western blotting analysis, further indicating that serum‑starvation induces apoptosis. Therefore, tongue carcinoma squamous cells in a serum‑free medium can simulate apoptosis related to the formation of tongue coating, which may offer guidance for future investigations about other factors.