Genetic regulation of cellular senescence and immortality in cultured human cells.

在年轻和永生化细胞中被抑制的细胞衰老相关基因在细胞衰老中被诱导，并且衰老表型由衰老相关基因的功能介导。衰老相关基因Ⅰ型胶原酶基因上游1.7kb的100 bp区域卡里两个对永生化敏感的顺式作用元件ISEI和ISE 2。两个ISE 2结合因子，一个假定的激活因子Pluto和一个假定的抑制因子Orpheus的相互作用，被认为是至关重要的调控胶原酶基因伴随着体外老化和永生化。这些cDNA克隆编码的蛋白质保留了ALL-1/ML/RX复合物的CXXC结构域，该结构域位于某些白血病细胞的染色体断裂点。其中一个cDNA编码与p33 NG 1肿瘤抑制因子高度相关的蛋白质。衰老相关的抑制因子Orpheus被发现与转录因子Oct-1相同。Oct-1蛋白与核纤层的组分核纤层蛋白B共定位于年轻和永生化细胞的核外周结构中。在衰老细胞中，Oct-1在核板层的凝聚消失，Oct-1蛋白弥散分布于整个细胞中。Oct-1可能通过形成异染色质样的高级染色质二级结构来抑制细胞衰老相关基因的表达，对这些永生化易感因子的精确鉴定将为我们了解体外衰老和永生化的内在机制提供更多信息。

The cellular senescence-associated genes that are repressed in young and immortalized cells are induced in cellular senescence and the senescent phenotypes are mediated by the functions of the senescence-associated genes. One of the senescence-associated genes, the type I collagenase gene, cary two immortaliation-susceptible cis-acting elements, ISEI and ISE2, located in a 100-bp region about 1.7kb upstream. The interplay of two ISE2-binding factors, a putative activator Pluto and a putative repressor Orpheus, was suggested to be crucial for regulation of the collagenase gene accompanying in vitro aging and immortalization.We isolated three novel cDNA clones as the candidate genes of the transcriptional activator Pluto by one hybrid screening method in yeast. The proteins coded by these cDNA clones conserve the CXXC domain of ALL-1/ML/RX complex that are located at the chromosomal breakpoints of certain leukemic cells. One of the these cDNAs encoded a protein highly related to p33NG1 tumor suppressor.The senescence-related repressor Orpheus was found to be identical to the transcription factor Oct-1. The Oct-1 protein was co-localized with a component of the nuclear lamina, lamin B,in the nuclear peripheral structure of young and immortalized cells. In senescent cells, the condensation of Oct-1 in the nuclear lamina was disappeared and the Oct-1 protein was diffusely distributed in the whole cells. Oct-1 seemed to repress the cellular senescence-associated genes by forming a heterochromatin-like higher ordered secondary structure of chromatin.Precise characterization of these immortalization-susceptible factors will give us much information concerning the intrinsic mechanism of in vitro aging and immortalization.