DNA Methyltransferase 1(DNMT1)Regulates Hypopharyngeal Carcinoma By Inducing 06-methylguanine-DNA Methyltransferase(MGMT)Expression

Hypopharyngeal cancer accounts for about 5%of head and neck cancer,poorly differentiated squamous cell carcinoma,with occult onset,high degree of malignancy,aggressive,poor prognosis,easy to relapse.In recent years,although the comprehensive treatment strategy based on surgical treatment has been continuously optimized,the 5-year survival rate is still about 40%.Therefore,looking for an important factor in the occurrence and development of tumors and exploring its mechanism of action,especially for the diagnosis and treatment of hypopharyngeal cancer.DNA methylation mediated by DNA methyltransferase(DNMTs)is an important epigenetic modification during tumorigenesis and development.DNMT1 is a key enzyme that maintains methylation after replication.In most tumors High expression.As an important DNA damage repair enzyme,06-Methylguanine-DNA methyltransferase(06-Methylguanine-DNA methyltransferase)can independently participate in DNA alkylation damage repair and reduce DNA mutation.Prevention plays an important role,but its precise regulation mechanism is not yet clear.It has been reported that DNMT1 is associated with the methylation status of CpG island in the promoter region of tumor suppressor gene.By inhibiting its transcription,the tumor suppressor gene is inactivated,thereby promoting the development of tumor.However,the effect of DNMT1 on the regulation of MGMT expression has not been reported in hypopharyngeal carcinoma.This study examined the expression of MGMT and DNMT1 in hypopharyngeal carcinoma and the methylation status of CpG island in promoter region of MGMT.To investigate the expression of DNMT1 in hypopharyngeal carcinoma FaDu cell line by interfering with the expression of MGMT and hypopharyngeal carcinoma Apoptosis,and its mechanism of action for a preliminary study.Objective:To investigate the expression of DNMT1 and MGMT in hypopharyngeal carcinoma and the methylation status of CpG island in MGMT promoter region and its relationship with clinical stage.To investigate the effect of DNMT1 on methylation status and protein expression of MGMT promoter in FaDu cells.To preliminary study of DNMT1 hypopharyngeal cancer FaDu cell apoptosis mechanism.Methods:Paraffin sections were made from 32 hypopharyngeal carcinoma tissues and 20 normal tissues.The expressions of DNMT1 and MGMT were detected by immunohistochemistry.PCR was used to detect the mRNA expression of MGMT and DNMTs.The following pharyngeal cancer FaDu cell lines were used as experimental subjects,DNMT1 siRNA was prepared and transfected into FaDu cells.The expression of DNMT1 was detected by immunofluorescence,real-time PCR,MSP and FCM detect DNMTland MGMT mRNA expression,MGMT promoter methylation status changes and apoptosis.Results:1.DNMT1 overexpression in hypopharyngeal carcinoma,immunohistochemical detection of DNMT1 protein mainly in the nucleus of hypopharyngeal cancer cells,a small amount of expression in the cell membrane,and pathological grade were significantly associated.2.MGMT was overexpressed in hypopharyngeal carcinoma.Immunohistochemistry showed that MGMT protein was mainly expressed in the cell membrane of hypopharyngeal carcinoma and a small amount was expressed in the nucleus.3.Real-time PCR detection found that DNMT1 mRNA expression in hypopharyngeal carcinoma was significantly higher than that in normal squamous epithelium,while MGMT mRNA expression was significantly lower than normal squamous epithelium.4.Hypopharyngeal carcinoma FaDu cells after DNMT1 siDNMTl interference,DNMT1 protein and mRNA levels in the table Up to a significant reduction.5.Decreased DNMT1 expression,the expression of MGMT protein and mRNA were significantly increased.6.Decreased DNMT1 expression the methylation of CpG island in MGMT gene promoter region was decreased.7.Decreased DNMT1 expression,the early apoptosis rate of FaDu cells was significantely increased.Conclusion:1.DNMT1 overexpression in hypopharyngeal carcinoma,and pathological grade were significantly correlated.2.DNMT1 regulates the hypermethylation of CpG island in promoter region of MGMT gene,resulting in the transcriptional inactivation,resulting in the decrease of expression,the inhibition of hypopharyngeal carcinoma cell apoptosis and the promotion of tumorigenesis and development.3.DNMT1 plays an important role in the malignant behavior of hypopharyngeal carcinoma,which may become a new target for the diagnosis and treatment of hypopharyngeal carcinoma.