Objective: To investigate the evolution pattern of the Runx3 gene 5'-CpG island ~3478 bp region methylation in human salivary gland adenoid cystic carcinoma (SGACC).
Methods: Quantitative MSP method was used to detect the methylation status of CpG island in various regions (No.1-10) of Runx3 promoter region, and Western blot was used for detection of the expression of Runx3 protein in 41 salivary gland SGACC samples and corresponding non-neoplastic salivary gland tissues. A Logistic model was used to analyze the risk ratio between the methylation status of CpG island in Runx3 gene and development of salivary SGACC, meanwhile, the possible association among the methylation of Runx3 gene, the clinicopathological parameters of SGACCs, and Runx3 protein expression was compared.
Results: The results of qMSP showed that the hypermethylation initially occurred at the most 5' region of the Runx3 CpG island and spread to the transcription start site. The methylation rate was highest in region No. 1 and No. 2 among the successive ten regions ranging from the 5' region to the transcription start site within the Runx3 CpG island, and lowest in the transcription start site both in SGACCs and normal salivary glands. Furthermore, there was no methylation in the transcription start site in nomal salivary glands tissues. Together with the results of Logistic model analysis, those results indicate that the transcription start site within the Runx3 promoter CpG island is critical for gene silencing. Western blot results revealed that the Runx3 protein level in SGACC was significantly lower than that in normal salivary glands (P < 0.01). In combination of the results of qMSP, it is presumed that the Runx3 gene methylation is one of the reason inducing the down-regulation of Runx3 in SGACCs.
Conclusions: Methylation of the Runx3 CpG island spreads from the most 5'-region to the transcription start site in human salivary gland adenoid cystic carcinoma, and the transcription start site may be a critical region for the methylation of Runx3. The evolution pattern of Runx3 gene methylation is related to the tumorigenesis of SGACCs.