Knockdown of TFAP2E results in rapid G₂/M transition in oral squamous cell carcinoma cells

TFAP2E is a member of the activator protein-2 transcription factor family and acts as a tumor suppressor in several types of cancer. Downregulation of TFAP2E expression is significantly associated with a shorter overall survival period in patients with oral squamous cell carcinoma (OSCC). To evaluate the molecular mechanisms by which TFAP2E suppresses the development or progression of OSCC, the present study investigated the effects of TFAP2E downregulation on OSCC-derived Ca9-22 and HSC-4 cells. The present study demonstrated that small interfering RNA mediated-knockdown of TFAP2E accelerated the proliferation of these OSCC cell lines compared with that in the control group, as determined by the standard water-soluble tetrazolium salt-8 assay. To analyze the cell cycle progression rate, the cell cycle distribution patterns of TFAP2E-knockdown and control cells cultured in the presence of nocodazole, which prevents the completion of mitosis, were analyzed by fluorescence-activated cell sorting at different time points. When analyzing cellular DNA contents, no major differences in cell cycle profiles were observed; however, the rate of increase in cells positive for histone H3 Serine 28 phosphorylation, a standard molecular marker of early M phase, was significantly higher in TFAP2E-knockdown cells than in the control cells. Collectively, these results suggested that TFAP2E may attenuate the proliferation of OSCC cells by regulating G(2)/M transition.