Inactivation of RUNX3 protein expression in tongue squamous cell carcinoma and its association with clinicopathological characteristics

The function of runt-related transcription factor 3 (RUNX3) in oral cancer remains controversial. The present study aimed to determine the status of RUNX3 protein expression and its association with clinicopathological characteristics in tongue squamous cell carcinomas (SCC). The present study used three pairs of tongue SCC and non-cancerous tissues to assess RUNX3 protein expression by western blot analysis, and two tongue SCC cell lines to determine RUNX3 protein localization by immunofluorescence and immunocytochemistry. Tissue microarray immunohistochemistry was performed to detect the clinical relevance of RUNX3 in 79 patients with tongue SCC. The results demonstrated that RUNX3 protein expression was reduced in tongue SCC tissues compared with in paired non-cancerous tissues. Similarly, the expression of RUNX3 was low in SCC25 and Cal27 cells, and was predominantly localized to the cytoplasm. In the 79 patients with tongue SCC, RUNX3 protein expression was presented in different manners in carcinoma nests and tumor stroma. RUNX3 in carcinoma nests (nRUNX3) exhibited nuclear positive staining in 24/79 samples, cytoplasmic mislocalization in 41/79 samples and was undetectable in 14/79 samples. RUNX3 in stroma (sRUNX3) exhibited nuclear positive staining in 40/79 samples and nuclear negative staining in 39/79 samples. Negative nRUNX3 expression was significantly associated with lymph node metastasis (P=0.014), clinical stage (P=0.027), and overall and disease-free survival (P=0.008 and P=0.007, respectively). In addition, negative sRUNX3 expression was associated with lymph node metastasis (P=0.003) and clinical stage (P=0.003); however, not with overall survival. The findings of the present study preliminarily suggested that cytoplasmic mislocalization of RUNX3 protein may be a common event in tongue SCC, and that sRUNX3 protein expression may be a potential prognostic biomarker.