Role of yeast CENP-A chaperone in DNA Damage Response

The centromeric protein-A (CENP-A) is an evolutionary conserved histone H3 variant that marks the identity of the centromeres. Several mechanisms regulate the centromeric deposition of CENP-A as its mislocalization causes erroneous chromosome segregation, leading to aneuploidy-based diseases, including cancers. The most crucial deposition factor is a CENP-A specific chaperone, HJURP (Scm3 in budding yeast), which specifically binds to CENP-A. However, the discovery of HJURP as a DDR (DNA damage repair) protein and evidence of its binding to Holliday junctions in vitro indicate a CENP-A-deposition-independent role of these chaperones. In this study, using budding yeast, we demonstrate that Scm3 is crucial for the DDR pathway as scm3 cells are sensitive to DNA damage. We further observe that the scm3 mutant genetically interacts with the rad52 DDR mutant and is compromised in activating DDR-mediated arrest. We demonstrate that Scm3 associates with the DNA damage sites and undergoes posttranslational modifications upon DNA damage. Overall, from this report and earlier studies on HJURP, we conclude that DDR functions of CENP-A chaperones are conserved across eukaryotes. Thus, the revelation that these chaperones confer genome stability in more than one pathway has clinical significance.

着丝粒蛋白A（CENP-A）是一类进化保守的组蛋白H3变体，可标记着丝粒的身份特征。由于CENP-A的异常定位会引发染色体分离错误，进而导致以非整倍体为特征的疾病（包括癌症），因此存在多种调控机制以确保CENP-A在着丝粒区域的正确沉积。其中最关键的沉积因子是CENP-A特异性分子伴侣HJURP（出芽酵母中对应为Scm3），该因子可特异性结合CENP-A。然而，HJURP作为DNA损伤修复（DDR，DNA damage repair）蛋白的发现，以及其体外结合霍利迪联结体（Holliday junctions）的实验证据，表明这类分子伴侣还存在不依赖CENP-A沉积的其他功能。本研究以出芽酵母为模型，证实Scm3在DNA损伤修复通路中发挥关键作用：scm3突变体细胞对DNA损伤具有超敏性。我们进一步发现，scm3突变体与rad52 DNA损伤修复突变体存在遗传互作，且其介导DNA损伤修复依赖的细胞周期阻滞的能力受损。实验证实，Scm3可招募至DNA损伤位点，并在DNA损伤刺激下发生翻译后修饰。综合本研究与此前针对HJURP的相关研究，我们认为CENP-A分子伴侣的DNA损伤修复功能在真核生物中具有进化保守性。因此，这类分子伴侣可通过多条通路维持基因组稳定性这一发现，具备重要的临床意义。