dna甲基化与肿瘤(编辑修改稿)

dna甲基化与肿瘤(编辑修改稿)内容摘要：

proaches which relied on differential restriction enzyme cleavage to distinguish methylated from unmethylated DNA. In this study, we demonstrate the use of MSP to identify promoter region hypermethylation changes associated with transcriptional inactivation in four important tumor suppressor genes (p16, p15, Ecadherin, and von HippelLindau) in human cancer. 8 Ahmad I, Rao DN. Chemistry and biology of DNA methyltransferases. Crit Rev Biochem MolBiol, 1996, 31: 361380. 9 Vertino PM , Yen RW, Gao J , et al. De novo methylation of CpG island sequences in human fibroblasts overexpressing DNA(cytosine 5) methyltransferase1Mol Cell Biol ,1996 ,16 (8) :4555 Abstract: Recent studies showing a correlation between the levels of DNA (cytosine5)methyltransferase (DNA MTase) enzyme activity and tumorigenicity have implicated this enzyme in the carcinogenic process. Moreover, hypermethylation of CpG islandcontaining promoters is associated with the inactivation of genes important to tumor initiation and progression. One proposed role for DNA MTase in tumorigenesis is therefore a direct role in the de novo methylation of these otherwise unmethylated CpG islands. In this study, we sought to determine whether increased levels of DNA MTase could directly affect CpG island methylation. A fulllength cDNA for human DNA MTase driven by the cytomegalovirus promoter was constitutively expressed in human fibroblasts. Individual clones derived from cells transfected with DNA MTase (HMT) expressed 1 to 50fold the level of DNA MTase protein and enzyme activity of the parental cell line or clones transfected with the control vector alone (Neo). To determine the effects of DNA MTase overexpression on CpG island methylation, we examined 12 endogenous CpG island loci in the HMT clones. HMT clones expressing or = 9fold the parental levels of DNA MTase activity were significantly hypermethylated relative to at least 11 Neo clones at five CpG island loci. In the HMT clones, methylation reached nearly 100% at susceptible CpG island loci with time in culture. In contrast, there was little change in the methylation status in the Neo clones over the same time frame. Taken together, the data indicate that overexpression of DNA MTase can drive the de novo methylation of susceptible CpG island loci, thus providing support for the idea that DNA MTase can contribute to tumor progression through CpG island methylationmediated gene inactivation. 10 Ehrlich M , Wang 5 methylcytosine in eukaryotic ,1981 ,212 :1350 11 Keith D et al. Differential mRNA expression of the human DNA methyltransferases (DNMTs) 1, 3a and 3b during the G0/G1 to S phase transition in normal and tumor Acids Research, 2020。 10: 2108 Abstract: DNA methylation is essential for mammalian development, Xchromosome inactivation, and imprinting yet aberrant methylation patterns are one of the most mon features of transformed cells. One of the proposed causes for these defects in the methylation machinery is overexpression of one or more of the three known catalytically active DNA methyltransferases (DNMTs) 1, 3a and 3b, yet there are clearly examples in which overexpression is minimal or nonexistent but global methylation anomalies persist. An alternative mechanism which could give rise to global methylation errors is the improper expression of one or more of the DNMTs during the cell cycle. To begin to study the latter possibility we examined the expression of the mRNAs for DNMT1, 3a and 3b during the cell cycle of normal and transformed cells. We found that DNMT1 and 3b levels were significantly downregulated in G0/G1 while DNMT3a mRNA levels were less sensitive to cell cycle alterations and were maintained at a slightly higher level in tumor lines 8 pared to normal cell strains. Enzymatic activity assays revealed a similar decrease in the overall methylation capacity of the cells during G0/G1 arrest and again revealed that a tumor cell line maintained a higher methylation capacity during arrest than a normal cell strain. These results reveal a new level of control exerted over the cellular DNA methylation machinery, the loss of which provides an alternative mechanism for the genesis of the aberrant methylation patterns observed in tumor cells. 12 Bender CM,Zingg JM,Jones PA. DNA methylation in bladder cancer[J ] . Pharm Aceutical Res,1998 ,15(2) :175. Abstract: DNA methylation is essential for normal embryonic development. Distinctive genomic methylation patterns must be formed and maintained with high fidelity to ensure the inactivities of specific promoters during development. The mutagenic and epigeic aspects of DNA methylation are especially interesting because they may lead to the inactivation of genes which are involved in human carcinogenesis. The mutagenicity of 5Methylcytosine (5mC) and the role of promoter hypermethylation in gene silencing, particularly in cancer, suggest a clinical significance for the design of novel DNA methylation inhibitors which may be utilized to reverse the effects of DNA methylation. 13 Ahujia N. Aging and DNA methylation in colorectal mucosa and cancer[J ] . Cancer Res ,1997 ,58 (23) :33703374. 14 Wheeler JM,Beck NE , Kim HC , et al . Mechanisms of inactivation ofmismatch repair genes in human colorectal cancer cell lines : the predominant role of Hmlh1[J ] . Proc Natl Acad Sci USA ,1999 ,96 (18) :1029610301. 15 彭正良 .甲状腺肿瘤相关基因甲基化研究进展 .国外医学生理、病理科学与临床分册， 2020， 25（ 2）： 126129 16 G. Strathdee and R. Brown. Aberrant DNA methylation in cancer:potential clinical interventions. Expert Rev Mol Med, 2020,3: 117. 17 Virmani AK, Rathi A, Sathyanarayana UG,et al: Aberrant methylation of the adenomatous polyposis coli (APC) gene promoter 1A in breastand lung carcinomas. Clin Cancer Res 7:19982020, 2020 Abstract: The adenomatous polyposis coli (APC) gene is a tumor suppre。