Velicescu Mihaela, Yu Jiamei, Herbert Brittney-Shea, Shay Jerry W, Granada Eileen, Dubeau Louis
University of Southern California/Norris Comprehensive Cancer Center, Department of Pathology, University of Southern California, Keck School of Medicine, Los Angeles, California 90089-9181, USA.
Cancer Res. 2003 Sep 15;63(18):5813-20.
Replicative immortality is achieved in vitro by overcoming two mortality checkpoints, M1 (senescence) and M2 (crisis). Cancer cells are thought to overcome M2 by activating telomerase, an enzyme believed to confer genomic stability in addition to maintaining telomeric sequences above a critical length. Here we show that a subset of cultured ovarian cystadenoma cells expressing SV40 large T-antigen, which allows bypassing of M1, develop a specific type of genomic instability, characterized by numerical (as opposed to structural) chromosomal alterations, that leads to non-telomere-based premature growth arrest/crisis. Cells recover from this type of growth arrest and stabilize their ploidy status without telomerase expression. In these cases, telomeres continue to shorten until a second, telomere-based growth arrest/crisis event is reached. Transfection of the catalytic subunit of telomerase does not immortalize cells harboring severe abnormalities in their DNA ploidy but results in immortalization of diploid cells. We conclude that changes in DNA ploidy constitute an important determinant of growth arrest that is independent of telomere attrition in a subset of SV40 large T-antigen-expressing cystadenoma cells. Reestablishment or emergence of ploidy stability, which is not always dependent on telomerase activation, is necessary for acquisition of the potential to achieve replicative immortality.
通过克服两个死亡检查点，即M1（衰老）和M2（危机），可在体外实现复制性永生。癌细胞被认为通过激活端粒酶来克服M2，端粒酶是一种除了能将端粒序列维持在临界长度以上外，还被认为能赋予基因组稳定性的酶。在此，我们表明，表达SV40大T抗原的培养卵巢囊腺瘤细胞亚群可绕过M1，发生一种特定类型的基因组不稳定，其特征为染色体数目（而非结构）改变，导致基于非端粒的过早生长停滞/危机。细胞可从这种类型的生长停滞中恢复，并在不表达端粒酶的情况下稳定其倍性状态。在这些情况下，端粒持续缩短，直至发生第二次基于端粒的生长停滞/危机事件。转染端粒酶催化亚基并不能使DNA倍性严重异常的细胞永生化，但可使二倍体细胞永生化。我们得出结论，DNA倍性变化是生长停滞（在表达SV40大T抗原的囊腺瘤细胞亚群中独立于端粒损耗）的一个重要决定因素。倍性稳定性的重建或出现（并不总是依赖于端粒酶激活）对于获得实现复制性永生的潜力是必要的。
