Institute of Molecular Oncology, Göttingen Center of Molecular Biosciences (GZMB), University Medical Center Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
Department of Molecular Structural Biology, Institute of Microbiology & Genetics, GZMB, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
Cell Rep. 2022 May 31;39(9):110879. doi: 10.1016/j.celrep.2022.110879.
The MDM2 oncoprotein antagonizes the tumor suppressor p53 by physical interaction and ubiquitination. However, it also sustains the progression of DNA replication forks, even in the absence of functional p53. Here, we show that MDM2 binds, inhibits, ubiquitinates, and destabilizes poly(ADP-ribose) polymerase 1 (PARP1). When cellular MDM2 levels are increased, this leads to accelerated progression of DNA replication forks, much like pharmacological inhibition of PARP1. Conversely, overexpressed PARP1 restores normal fork progression despite elevated MDM2. Strikingly, MDM2 profoundly reduces the frequency of fork reversal, revealed as four-way junctions through electron microscopy. Depletion of RECQ1 or the primase/polymerase (PRIMPOL) reverses the MDM2-mediated acceleration of the nascent DNA elongation rate. MDM2 also increases the occurrence of micronuclei, and it exacerbates camptothecin-induced cell death. In conclusion, high MDM2 levels phenocopy PARP inhibition in modulation of fork restart, representing a potential vulnerability of cancer cells.
MDM2 癌蛋白通过物理相互作用和泛素化拮抗肿瘤抑制因子 p53。然而，即使在功能性 p53 缺失的情况下，它也能维持 DNA 复制叉的进展。在这里，我们表明 MDM2 结合、抑制、泛素化和破坏多聚（ADP-核糖）聚合酶 1（PARP1）。当细胞内 MDM2 水平增加时，这会导致 DNA 复制叉的加速进展，类似于 PARP1 的药理学抑制。相反，过表达的 PARP1 尽管 MDM2 水平升高，但仍能恢复正常的叉进展。引人注目的是，MDM2 大大降低了叉反转的频率，通过电子显微镜显示为四叉结。RECQ1 或引发酶/聚合酶（PRIMPOL）的耗竭可逆转 MDM2 介导的新生 DNA 延伸速率的加速。MDM2 还增加了微核的发生频率，并加剧了喜树碱诱导的细胞死亡。总之，高 MDM2 水平在调节叉重新启动方面模拟了 PARP 抑制，代表了癌细胞的潜在脆弱性。
