Iwano Tomohiko, Tachibana Makoto, Reth Michael, Shinkai Yoichi
Experimental Research Center for Infectious Diseases, Institute for Virus Research, Kyoto University, Kyoto, Japan.
J Biol Chem. 2004 Jan 9;279(2):1442-8. doi: 10.1074/jbc.M309138200. Epub 2003 Oct 14.
Telomeres are comprised of telomeric DNA sequences and associated binding molecules. Their structure functions to protect the ends of linear chromosomes and ensure chromosomal stability. One of the mammalian telomere-binding factors, TRF1, localizes telomeres by binding to double-stranded telomeric DNA arrays. Because the overexpression of wild-type and dominant-negative TRF1 induces progressive telomere shortening and elongation in human cells, respectively, a proposed major role of TRF1 is that of a negative regulator of telomere length. Here we report another crucial function of TRF1 in telomeres. In conditional mouse TRF1 null mutant embryonic stem cells, TRF1 deletion induced growth defect and chromosomal instability. Although no clear telomere shortening or elongation was observed in short term cultured TRF1-deficient cells, abnormal telomere signals were observed, and TRF1-interacting telomere-binding factor, TIN2, lost telomeric association. Furthermore, another double-stranded telomeric DNA-binding factor, TRF2, also showed decreased telomeric association. Importantly, end-to-end fusions with detectable telomere signals at fusion points accumulated in TRF1-deficient cells. These results strongly suggest that TRF1 interacts with other telomere-binding molecules and integrates into the functional telomere structure.
端粒由端粒DNA序列和相关的结合分子组成。它们的结构起到保护线性染色体末端并确保染色体稳定性的作用。哺乳动物端粒结合因子之一TRF1，通过与双链端粒DNA阵列结合来定位端粒。由于野生型和显性负性TRF1的过表达分别在人类细胞中诱导端粒逐渐缩短和延长，因此推测TRF1的主要作用是作为端粒长度的负调节因子。在此我们报告TRF1在端粒中的另一个关键功能。在条件性小鼠TRF1基因敲除突变胚胎干细胞中，TRF1缺失诱导生长缺陷和染色体不稳定。尽管在短期培养的TRF1缺陷细胞中未观察到明显的端粒缩短或延长，但观察到异常的端粒信号，并且与TRF1相互作用的端粒结合因子TIN2失去了端粒关联。此外，另一种双链端粒DNA结合因子TRF2也显示出端粒关联减少。重要的是，在TRF1缺陷细胞中积累了在融合点具有可检测端粒信号的端对端融合。这些结果强烈表明TRF1与其他端粒结合分子相互作用并整合到功能性端粒结构中。
