Pituitary tumor-transforming gene 1 regulates the senescence and apoptosis of oral squamous cell carcinoma in a p21-dependent DNA damage response manner

Pituitary tumor-transforming gene 1 (PTTG1), also known as securin, is a proto-oncogene involved in the development of various cancers by promoting cell proliferation and mobility. However, its underlying biological mechanisms in oral squamous cell carcinoma (OSCC) progression remain unclear. in the present study, it was sought to elucidate the role of PTTG1 as an oncogene in OSCC progression and was attempted to unravel the underlying mechanism and impact of PTTG1 expression on cell cycle, cell death, and cellular senescence. The effect of double strand break on PTTG1 expression was investigated in OSCC growth. To identify the role of PTTG1 in OSCC growth, the cell viability and senescence was analyzed by EdU and senescence-associated beta-galactosidase (SA-beta-gal) assay, respectively. To verify the DNA damage-induced senescence of PTTG1, the chromosomal damage in OSCC was analyzed in vitro. Finally, the effect of PTTG1 on tumor growth and gene expression related to cell viability and DNA damaged-induced senescence was investigated in vivo. PTTG1 expression was compared between OSCC and healthy patient samples (n=32) using reverse transcription-quantitative PCR and immunohistochemistry; and it was found that PTTG1 expression was upregulated in OSCC. Small interfering RNA-mediated knockdown of PTTG1 in two OSCC cell lines revealed that PTTG1 downregulation significantly inhibited cell proliferation and arrested the cell cycle pathway as evidenced by changes in checkpoint genes (such as cyclin D1, E and B1). PTTG1 knockdown also increased apoptosis, as evidenced by the upregulation of apoptotic genes [such as cleaved (c-) Caspase-7 and c-poly (ADP-ribose) polymerase]. Moreover, PTTG1 downregulation promoted cellular senescence, as shown by western blotting and SA-beta-gal staining. Finally, senescence-induced DNA damage was observed in OSCC cells, which accelerates genomic instability, through chromosomal damage analysis. Taken together, the present findings suggested that PTTG1 acts as a proto-oncogene; regulates cell proliferation, cell cycle, cellular senescence and DNA damage in OSCC; and may serve as a novel diagnostic biomarker and potential therapeutic target for OSCC.