Khajavi M, Tari A M, Patel N B, Tsuji K, Siwak D R, Meistrich M L, Terry N H, Ashizawa T
Department of Neurology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Hum Mol Genet. 2001 Apr 1;10(8):855-63. doi: 10.1093/hmg/10.8.855.
In myotonic dystrophy type 1 (DM1), an expanded CTG repeat shows repeat size instability in somatic and germ line tissues with a strong bias toward further expansion. To investigate the mechanism of this expansion bias, 29 DM1 and six normal lymphoblastoid cell lines (LBCLs) were single-cell cloned from blood cells of 18 DM1 patients and six normal subjects. In all 29 cell lines, the expanded CTG repeat alleles gradually shifted toward further expansion by "step-wise" mutations. Of these 29 cell lines, eight yielded a rapidly proliferating mutant with a gain of large repeat size that became the major allele population, eventually replacing the progenitor allele population. By mixing cell lines with different repeat expansions, we found that cells with larger CTG repeat expansion had a growth advantage over those with smaller expansions in culture. This growth advantage was attributable to increased cell proliferation mediated by Erk1,2 activation, which is negatively regulated by p21(WAF1). This phenomenon, which we designated "mitotic drive" , is a novel mechanism which can explain the expansion bias of DM1 CTG repeat instability at the tissue level, on a basis independent of the DNA-based expansion models. The lifespans of the DM1 LBCLs were significantly shorter than normal cell lines. Thus, we propose a hypothesis that DM1 LBCLs drive themselves to extinction through a process related to increased proliferation.
在1型强直性肌营养不良症（DM1）中，扩增的CTG重复序列在体细胞和生殖系组织中表现出重复序列大小的不稳定性，且强烈倾向于进一步扩增。为了研究这种扩增偏向的机制，从18名DM1患者和6名正常受试者的血细胞中对29个DM1和6个正常淋巴母细胞系（LBCL）进行了单细胞克隆。在所有29个细胞系中，扩增的CTG重复等位基因通过“逐步”突变逐渐向进一步扩增转变。在这29个细胞系中，有8个产生了一个快速增殖的突变体，其重复序列大小增加，成为主要的等位基因群体，最终取代了祖代等位基因群体。通过将具有不同重复序列扩增的细胞系混合，我们发现在培养中，具有较大CTG重复扩增的细胞比具有较小扩增的细胞具有生长优势。这种生长优势归因于由Erk1,2激活介导的细胞增殖增加，而Erk1,2激活受p21（WAF1）负调控。我们将这种现象称为“有丝分裂驱动”，这是一种新的机制，可以在独立于基于DNA的扩增模型的基础上，解释DM1 CTG重复序列不稳定性在组织水平上的扩增偏向。DM1 LBCL的寿命明显短于正常细胞系。因此，我们提出一个假设，即DM1 LBCL通过与增殖增加相关的过程驱使自身走向灭绝。
