可逆的组蛋白乙酰化调控p16的表达

p16^INK4a通过抑制CDK4/6的活性而在细胞周期进行中发挥重要的作用,研究发现,组蛋白乙酰转移酶p300能促进p16^INK4a启动子活性,而组蛋白去乙酰化酶HDAC3/4能够逆转由p300介导的p16^INK4a启动子活性的增加,HDAC3/4能够降低p16^INK4a mRNA和蛋白质的水平．染色质免疫沉淀(ChIP)实验结果表明转染p300表达质粒能够逆转由HDAC3/4介导的p16^INK4a启动子组蛋白的低乙酰化状态．此外,免疫荧光实验结果表明HDAC4的核质穿梭起着重要的作用．免疫印迹和染色质免疫沉淀实验证明HDAC的抑制剂丁酸钠盐(NaBu)能通过诱导组蛋白的高乙酰化而促进p16^INK4a的表达．基于这些实验结果,推测出可逆的组蛋白乙酰化参与p16^INK4a基因转录调控的模型．     

三氟拉嗪通过诱导p16INK4a抑制BGC-823细胞增殖

为探索三氟拉嗪（trifluoperazine, TFP）抗肿瘤作用机制,对胃癌BGC-823细胞进 行TFP（5、10 μmol/L）处理后,利用计数法、BrdU脉冲标记法、Western印迹等方法从细胞形态、细胞增殖、S期细胞百分比以及相关因子表达水平等方面进行分析. 结果显示,TFP处理后,细胞形态发生明显改变,细胞增殖受到明显抑制且呈时间计量 效应关系;S期细胞比例下降;p16INK4a表达水平升高.为进一步研究TFP诱导 p16INK4a表达的分子机制,本实验采用插入p16INK4a启动子片段及荧光素酶报告系统 的载体pGL3-Basic-p16INK4a（-967~-165 bp）,研究了TFP在转录水平对p16INK4a启 动子活性的影响.结果表明, TFP能够提高p16INK4a的启动子活性.上述结果提示,TFP 通过诱导p16INK4a表达抑制BGC-823细胞增殖.     

DNA methyltransferase controls stem cell aging by regulating BMI1 and EZH2 through microRNAs

Epigenetic regulation of gene expression is well known mechanism that regulates cellular senescence of cancer cells. Here we show that inhibition of DNA methyltransferases (DNMTs) with 5-azacytidine (5-AzaC) or with specific small interfering RNA (siRNA) against DNMT1 and 3b induced the cellular senescence of human umbilical cord blood-derived multipotent stem cells (hUCB-MSCs) and increased p16(INK4A) and p21(CIP1/WAF1) expression. DNMT inhibition changed histone marks into the active forms and decreased the methylation of CpG islands in the p16(INK4A) and p21(CIP1/WAF1) promoter regions. Enrichment of EZH2, the key factor that methylates histone H3 lysine 9 and 27 residues, was decreased on the p16(INK4A) and p21(CIP1/WAF1) promoter regions. We found that DNMT inhibition decreased expression levels of Polycomb-group (PcG) proteins and increased expression of microRNAs (miRNAs), which target PcG proteins. Decreased CpG island methylation and increased levels of active histone marks at genomic regions encoding miRNAs were observed after 5-AzaC treatment. Taken together, DNMTs have a critical role in regulating the cellular senescence of hUCB-MSCs through controlling not only the DNA methylation status but also active/inactive histone marks at genomic regions of PcG-targeting miRNAs and p16(INK4A) and p21(CIP1/WAF1) promoter regions.