Gong Zhi-Yuan, Kidoya Hiroyasu, Mohri Tomomi, Han Yinglu, Takakura Nobuyuki
Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
Department of Signal Transduction, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan; Japan Science and Technology Agency, Chiyoda-ku, Tokyo, Japan.
PLoS One. 2014 Oct 21;9(10):e110483. doi: 10.1371/journal.pone.0110483. eCollection 2014.
SLD5 is a member of the GINS complex composed of PSF1, PSF2, PSF3 and SLD5, playing a critical role in the formation of the DNA replication fork with CDC45 in yeast. Previously, we had isolated a PSF1 orthologue from a murine hematopoietic stem cell DNA library and were then able to identify orthologues of all the other GINS members by the yeast two hybrid approach using PSF1 as the bait. These GINS orthologues may also function in DNA replication in mammalian cells because they form tetrameric complexes as observed in yeast, and gene deletion mutants of both PSF1 and SLD5 result in a lack of epiblast proliferation and early embryonic lethality. However, we found that PSF1 is also involved in chromosomal segregation in M phase, consistent with recent suggestions that homologues of genes associated with DNA replication in lower organisms also regulate cellular events other than DNA replication in mammalian cells. Here we analyzed the function of SLD5 other than DNA replication and found that it is active in DNA damage and repair. Attenuation of SLD5 expression results in marked DNA damage in both normal cells and cancer cells, suggesting that it protects against DNA damage. Attenuation of SLD5 delays the DNA repair response and cell cycle restoration in normal cells but not in cancer cells. These findings suggest that SLD5 might represent a therapeutic target molecule acting at the level of tumor stromal cells rather than the cancerous cells themselves, because development of the tumor microenvironment could be delayed or disrupted by the suppression of its expression in the normal cell types within the tumor.
SLD5是由PSF1、PSF2、PSF3和SLD5组成的GINS复合物的成员之一，在酵母中与CDC45一起在DNA复制叉的形成中发挥关键作用。此前，我们从鼠造血干细胞DNA文库中分离出一个PSF1直向同源物，然后能够通过以PSF1为诱饵的酵母双杂交方法鉴定出所有其他GINS成员的直向同源物。这些GINS直向同源物可能也在哺乳动物细胞的DNA复制中发挥作用，因为它们如在酵母中观察到的那样形成四聚体复合物，并且PSF1和SLD5的基因缺失突变体均导致外胚层增殖缺乏和早期胚胎致死。然而，我们发现PSF1也参与M期的染色体分离，这与最近的观点一致，即低等生物中与DNA复制相关的基因同源物在哺乳动物细胞中也调节除DNA复制之外的细胞事件。在这里，我们分析了SLD5除DNA复制之外的功能，发现它在DNA损伤和修复中具有活性。SLD5表达的减弱在正常细胞和癌细胞中均导致明显的DNA损伤，表明它可防止DNA损伤。SLD5的减弱会延迟正常细胞而非癌细胞中的DNA修复反应和细胞周期恢复。这些发现表明，SLD5可能代表一种作用于肿瘤基质细胞水平而非癌细胞本身的治疗靶点分子，因为肿瘤微环境的发育可能会因抑制肿瘤内正常细胞类型中的其表达而延迟或中断。
