Yes-associated protein promotes cell proliferation by activating Fos Related Activator-1 in oral squamous cell carcinoma

In our previous study, we established an in vitro cellular carcinogenesis model of oral squamous cell carcinoma (OSCC), including a human immortalized oral epithelial cell (HIOEC) and a cancerous cell line (HB96). Microarray analysis showed that the gene encoding Yes-associated protein (YAP) was significantly increased in HB96 cells compared with HIOEC cells. But the underlying mechanism of YAP on oncogenesis, especially its downstream targets, are still not clear. YAP expression in OSCC cell lines and tissue specimens were investigated by using real-time PCR, western blotting and immunohistochemistry staining. YAP put-back plasmid with four mutation sites after YAP-siRNA interference was constructed by site-directed mutagenesis. Cell growth and colony formation were observed after YAP-siRNA interference or YAP put-back again in CAL27 cells. YAP expression was increased in the cellular carcinogenesis models and the clinical samples from primary OSCC patients. Inhibition of YAP by siRNA interference in CAL27 cells significantly inhibited cell proliferation and colony formation in soft agar, but these abilities were rescued when YAP was put-back again. At the same time, Fos Related Activator-1 (Fra-1) was down-regulated when YAP was inhibited by siRNA interference while Fra-1 was rescued when YAP was put-back again. Immunohistochemistry results also indicated that higher levels of YAP were significantly associated with Fra-1 overexpression in OSCC clinical samples. YAP could promote cell proliferation by activating transcription factor Fra-1 in oral squamous cell carcinoma.