Molecular studies on mammalian telomerase

端粒酶是一种核糖核蛋白复合物，能从头合成端粒富含G链的DNA。端粒酶是一种特殊的逆转录酶，含有催化组分TERT和模板RNA TR。为了更好地了解端粒酶的调控机制，本研究首先建立了TERT-T基因<-1->敲除小鼠。第一代TERT 1/2<-1->敲除小鼠没有显示任何表型，表明端粒酶催化蛋白本身的缺失不影响小鼠发育。然而，当TERT-A<-1->小鼠交配以保持该细胞系不存在端粒酶时，第五代小鼠显示出显著营养不良的生殖细胞系细胞。这些结果表明，生殖细胞是特别敏感的端粒长度减少。我们和其他人已经证明，TERT基因表达水平在调节细胞端粒酶活性中起主要作用。虽然已有报道，Myc、Sp1、ER等转录因子参与了细胞凋亡的调控， 关于我们 在TERT表达中，调节TERT的机制的细节，特别是在正常体细胞中，仍然是未知的。我们研究了正常人外周血淋巴细胞作为一个模型系统。我们发现转录因子USF 1和USF 2在体外正调控TERT启动子。已知USF 1和2的截短形式mini-USF 1和mini-USF 2通过选择性剪接从相同基因产生。有趣的是，我们证明了mini-USF 1和2在体外负调控启动子。人外周血淋巴细胞大多处于静息状态，不具有端粒酶活性。当外部刺激作用于静息淋巴细胞时，它们开始增殖，同时开始显示端粒酶活性。我们发现，负调节，迷你USFs存在于静息细胞，但不存在于活化的淋巴细胞。相反，正调节因子全长USF存在于静息和生长的淋巴细胞中。这些结果表明，迷你USFs可能有显着的负面影响，完全USFs在控制TERT的表达。少

Telomerase is a ribonucleoprotein complex that synthesizes telomeric G-rich strand DNA de novo. It is a specialized reverse transcriptase, containing the catalytic component, TERT and the template RNA, TR.To better understand regulation mechanisms of telomerase, in this study, we first established TERT^<-1-> knockout mice. The first generation of TERT^<-1-> knockout mice did not show any phenotype, indicating that the absence of telomerase catalytic protein by itself does not affect mouse development. However, when TERT^<-1-> mice were mated to keep the line absent for telomerase, the fifth generation mice showed significantly hypotrophic germ line cells. These results indicate that germ cells are particularly sensitive to telomere length reduction. We and others have already demonstrated that TERT gene expression levels have a primary role in regulating telomerase activity in cells. Although it has been reported that several transcription factors, including Myc, Sp1, ER, are involved … More in TERT expression, details of mechanisms regulating TERT, especially in normal somatic cells, remain largely unknown. We have studied normal human peripheral lymphocytes as a model system. We found that the transcription factors USF1 and 2 positively regulate the TERT promoter in vitro. Truncated forms of USF1 and 2, mini-USF1 and mini-USF2, are known to be produced from the same genes by alternative splicing. Interestingly, we demonstrated that mini-USF1 and 2 negatively regulate the promoter in vitro. Human peripheral lymphocytes are mostly resting and do not possess telomerase activity. Upon external stimuli applied to resting lymphocytes, they start proliferation and simultaneously begin to show telomerase activity. We found that the negative regulator, mini-USFs are present in resting cells but not in activated lymphocytes. In contrast, the positive regulator, full length USFs are present both in resting and growing lymphocytes. These results suggest that mini-USFs might have dominant negative effects on full USFs in controlling TERT expression. Less