Ouellette M M, Liao M, Herbert B S, Johnson M, Holt S E, Liss H S, Shay J W, Wright W E
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9039, USA.
J Biol Chem. 2000 Apr 7;275(14):10072-6. doi: 10.1074/jbc.275.14.10072.
Human fibroblasts expressing the catalytic component of human telomerase (hTERT) have been followed for 250-400 population doublings. As expected, telomerase activity declined in long term culture of stable transfectants. Surprisingly, however, clones with average telomere lengths several kilobases shorter than those of senescent parental cells continued to proliferate. Although the longest telomeres shortened, the size of the shortest telomeres was maintained. Cells with subsenescent telomere lengths proliferated for an additional 20 doublings after inhibiting telomerase activity with a dominant-negative hTERT mutant. These results indicate that, under conditions of limiting telomerase activity, cis-acting signals may recruit telomerase to act on the shortest telomeres, argue against the hypothesis that the mortality stage 1 mechanism of cellular senescence is regulated by telomere positional effects (in which subtelomeric loci silenced by long telomeres are expressed when telomeres become short), and suggest that catalytically active telomerase is not required to provide a protein-capping role at the end of very short telomeres.
表达人端粒酶催化成分（hTERT）的人成纤维细胞已传代培养250 - 400次群体倍增。正如预期的那样，稳定转染子的长期培养中端粒酶活性下降。然而，令人惊讶的是，平均端粒长度比衰老亲代细胞短几千碱基的克隆仍继续增殖。尽管最长的端粒缩短了，但最短端粒的长度保持不变。在用显性负性hTERT突变体抑制端粒酶活性后，端粒长度处于亚衰老状态的细胞又增殖了20次群体倍增。这些结果表明，在端粒酶活性受限的条件下，顺式作用信号可能募集端粒酶作用于最短的端粒，这与细胞衰老的死亡阶段1机制受端粒位置效应调控的假说相悖（该假说认为，当端粒变长时被沉默的亚端粒位点在端粒变短时会被表达），并表明在极短端粒末端提供蛋白质封端作用并不需要具有催化活性的端粒酶。
