Proteasome inhibition rescues clinically significant unstable variants of the mismatch repair protein Msh2
Proteasome inhibition rescues clinically significant unstable variants of the mismatch repair protein Msh2
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DOI：
10.1073/pnas.1215510110
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发表时间：
2013-01-02
影响因子：
11.1
通讯作者：
Gammie, Alison
中科院分区：
文献类型：
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作者：
Arlow, Tim;Scott, Kristan;Gammie, Alison
MSH2是真核生物中DNA错配修复识别所必需的。人类MSH2中的有害突变占与常见遗传性癌症综合征相关的等位基因的大约一半。此前，我们使用酵母作为模型系统对临床鉴定的Msh 2错义突变进行了表征，发现DNA错配修复缺陷的最常见原因是Msh 2蛋白变体水平低。在这里，我们表明，增加蛋白质周转是负责细胞水平降低。增加基因剂量，超过一半的错义等位基因完全恢复功能。滴定实验显示，将一种变体的表达水平提高至低于野生型水平可恢复错配修复，这表明恢复功能并不总是需要过表达。我们发现泛素介导的蛋白酶体降解途径是Msh2变体营业额增加的主要机制，并将主要的泛素连接酶确定为San1。删除San1恢复了除一种变体外的所有变体的蛋白质水平，但没有提高野生型Msh2水平。不稳定的变体与San1相互作用，而野生型Msh2没有。此外，san1 Delta抑制不稳定变体的错配修复缺陷。具有医学意义的是，临床批准的药物硼替佐米部分恢复了低水平变体的蛋白质水平和错配修复功能，并逆转了对顺铂（一种常见的化疗药物）的耐药性。我们的研究结果为某些传统化疗难治的错配修复缺陷型癌症的创新治疗方案提供了基础。
MSH2 is required for DNA mismatch repair recognition in eukaryotes. Deleterious mutations in human MSH2 account for approximately half of the alleles associated with a common hereditary cancer syndrome. Previously, we characterized clinically identified MSH2 missense mutations, using yeast as a model system, and found that the most common cause of defective DNA mismatch repair was low levels of the variant Msh2 proteins. Here, we show that increased protein turnover is responsible for the reduced cellular levels. Increasing gene dosage of more than half of the missense alleles fully restored function. A titration experiment revealed that raising the expression level of one variant to less than wildtype levels restored mismatch repair, suggesting that overexpression is not always required to regain function. We found that the ubiquitin-mediated proteasome degradation pathway is the major mechanism for increased turnover of the Msh2 variants and identified the primary ubiquitin ligase as San1. Deletion of San1 restored protein levels for all but one variant, but did not elevate wild-type Msh2 levels. The unstable variants interacted with San1, whereas wild-type Msh2 did not. Additionally, san1 Delta suppressed the mismatch repair defect of unstable variants. Of medical significance, the clinically approved drug Bortezomib partially restored protein levels and mismatch repair function for low-level variants and reversed the resistance to cisplatin, a common chemotherapeutic. Our results provide the foundation for an innovative therapeutic regime for certain mismatch-repair-defective cancers that are refractory to conventional chemotherapies.