Different phenotypic consequences of simultaneous versus stepwise Apc loss.
Different phenotypic consequences of simultaneous versus stepwise Apc loss.
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同时与逐步APC丢失的不同表型后果。
DOI：
10.1038/onc.2011.385
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发表时间：
2012-04-19
期刊：
影响因子：
8
通讯作者：
Liskay, R. M.
中科院分区：
文献类型：
--
作者：
Fischer, J. M.;Miller, A. J.;Shibata, D.;Liskay, R. M.
APC被认为是结直肠癌（CRC）的看门人。具有杂合APC突变的细胞具有改变的表达谱，这表明第一次APC击中可能有助于为随后的转化奠定基础。因此，我们测量了转化效率后，我们已经指定为“同时”与“逐步”的APC损失。我们将条件Apc等位基因（ApcCKO）与Cre报告基因和框架外Cre等位基因（Pms 2cre）相结合，该等位基因通过单细胞中的移码突变而发挥功能。一个Apc等位基因（ApcCKO/+）的丢失几乎没有影响，而同时丢失两个Apc等位基因（ApcCKO/CKO）导致克隆扩增增加（隐窝分裂），与Apc的看门人功能一致。有趣的是，我们的分析显示，ApcCKO/CKO小鼠中大多数Apc缺陷型隐窝表现正常，只有17%的隐窝发生形态学转化，包括β-连环蛋白失调。为了确定Apc逐步丢失后转化效率是否不同，我们将ApcCKO与种系突变等位基因ApcMin或Apc 1638 N结合。逐步Apc丢失（ApcMin/CKO或Apc 1638 N/CKO）后的转化效率增加了5倍，基本上所有的Apc缺陷细胞都发育不良。总之，我们的数据表明，看门人功能的Apc由两个角色，克隆扩张和形态转化，因为同时Apc的损失往往会导致隐匿性克隆扩张没有形态转化，而逐步Apc的损失更经常导致可见的肿瘤。最后，APC缺陷细胞在某些情况下可以保留正常表型是出乎意料的，并且可能对预防CRC的监测策略具有临床意义。
APC is considered a gatekeeper for colorectal cancer (CRC). Cells with heterozygous APC mutations have altered expression profiles suggesting that the first APC hit may help set the stage for subsequent transformation. Therefore, we measured transformation efficiency following what we have designated as “simultaneous” versus “stepwise” Apc loss. We combined a conditional Apc allele (ApcCKO) with a Cre reporter gene and an out-of-frame Cre allele (Pms2cre) that stochastically becomes functional by a frameshift mutation in single cells. Loss of one Apc allele (ApcCKO/+) had little consequence, whereas simultaneous loss of both Apc alleles (ApcCKO/CKO) resulted in increased clonal expansion (crypt fission), consistent with the gatekeeper function of Apc. Interestingly, our analyses showed that most of the Apc-deficient crypts in ApcCKO/CKO mice appeared normal, with morphologic transformation, including β-catenin deregulation, occurring in only 17% of such crypts. To determine whether transformation efficiency was different following stepwise Apc loss, we combined ApcCKO with a germline mutant allele, either ApcMin or Apc1638N. Transformation efficiency following stepwise Apc loss (ApcMin/CKO or Apc1638N/CKO) was increased 5-fold and essentially all of the Apc-deficient cells were dysplastic. In summary, our data suggest that the gatekeeper function of Apc consists of two roles, clonal expansion and morphologic transformation, because simultaneous Apc loss frequently leads to occult clonal expansion without morphologic transformation, whereas stepwise Apc loss more often results in visible neoplasia. Finally, that Apc-deficient cells in certain scenarios can retain a normal phenotype is unexpected and may have clinical implications for surveillance strategies to prevent CRC.
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