The expression and clinical significance of Bmi-1 gene in oral leukoplakia with different prognosis

Abstract

Objective: To detect the expression of Bmi-1 in oral leukoplakia (OL) cells and tissues, and analyze its role and clinical significance in the malignant transformation of OL. Methods: Immunohistochemistry was used to evaluate Bmi-1 expression in OL samples from 109 patients (51 males, 58 females, age range: 18-74 years) who were treated in the Department of Stomatology, the Affiliated Wuxi People's Hospital of Nanjing Medical University and the Center of Stomatology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, between 1996 and 2018. The correlation between Bmi-1 expression level and clinicopathological parameters and prognosis in patients with OL was analyzed. The mRNA and protein expression levels of Bmi-1 gene in normal oral mucosal epithelial cells, OL cells, oral squamous cell carcinoma (OSCC) cells, OL tissues and paired adjacent normal tissues were detected by real-time PCR and Western blotting. The effects of Bmi-1 on the proliferation, colony formation and apoptosis were investigated by silencing expression of Bmi-1 in OL cell lines Leuk-1. Results: The protein level of Bmi-1 in OL tissue with severe and mild dysplasia was statistically different (6 819±994 vs 4 713±372, P=0.017). The OSCC-free survival rate of OL patients with high Bmi-1 expression was 65.5% (36/55), which was lower than that of OL patients with low Bmi-1 expression (88.9%, 48/54, P=0.003). Multivariate Cox proportional analysis indicated that Bmi-1 expression was the independent predictor for malignant transformation of OL (HR=2.522, 95%CI: 1.128-5.640, P=0.024). The mRNA level of Bmi-1 in OL specimens was 0.455±0.120, which was higher than that in paired adjacent normal tissues (0.063±0.009, P=0.014). The Bmi-1 mRNA level in malignant transformed OL specimens was (1.405±0.397), which was higher than that in untransformed OL specimens (0.145±0.017, P<0.001). After transfection of Bmi-1-shNC and Bmi-1-shRNA2 adenovirus into OL cell line Leuk-1, there were significant differences in the number of clone formation (824±40 vs 414±38, P=0.002) and apoptosis rate (17.7%±2.3% vs 36.0%±2.0%, P=0.004). Conclusions: The up-regulation of Bmi-1 expression promotes the malignant biological behavior of OL cells. Bmi-1 expression can be used as a predictor for malignant transformation of OL.