Devlin Hong-Lin, Mack Phillip C, Burich Rebekah A, Gumerlock Paul H, Kung Hsing-Jien, Mudryj Maria, deVere White Ralph W
Department of Internal Medicine, University of California, Davis, School of Medicine, 4860 Y Street, Suite 3500, Sacramento, CA 95817, USA.
Mol Cancer Res. 2008 May;6(5):808-18. doi: 10.1158/1541-7786.MCR-07-2027.
p53R2 is a p53-inducible ribonucleotide reductase that contributes to DNA repair by supplying deoxynucleotide triphosphate pools in response to DNA damage. In this study, we found that p53R2 was overexpressed in prostate tumor cell lines compared with immortalized prostatic epithelial cells and that the protein was induced upon DNA damage. We investigated the effects of p53R2 silencing on DNA damage in LNCaP cells (wild-type p53). Silencing p53R2 potentiated the apoptotic effects of ionizing radiation and doxorubicin treatment as shown by increased sub-G(1) content and decreased colony formation. This sensitizing effect was specific to DNA-damaging agents. Comet assay and gamma-H2AX phosphorylation status showed that the decreased p53R2 levels inhibited DNA repair. Silencing p53R2 also reduced the levels of p21(WAF1/CIP1) at the posttranscriptional level, suggesting links between the p53-dependent DNA repair and cell cycle arrest pathways. Using LNCaP sublines stably expressing dominant-negative mutant p53, we found that the sensitizing effect of p53R2 silencing is mediated by p53-dependent apoptosis pathways. In the LNCaP sublines (R273H, R248W, and G245S) that have defects in inducing p53-dependent apoptosis, p53R2 silencing did not potentiate DNA damage-induced apoptosis, whereas p53R2 silencing was effective in a LNCaP subline (P151S) which retains the ability to induce p53-dependent apoptosis. This study shows that p53R2 is a potential therapeutic target that could be used to enhance the effectiveness of ionizing radiation or DNA-damaging chemotherapy in a subset of patients with prostate cancer.
p53R2是一种p53诱导型核糖核苷酸还原酶，通过在DNA损伤时提供三磷酸脱氧核苷酸库来促进DNA修复。在本研究中，我们发现与永生化前列腺上皮细胞相比，p53R2在前列腺肿瘤细胞系中过表达，且该蛋白在DNA损伤时被诱导。我们研究了p53R2沉默对LNCaP细胞（野生型p53）DNA损伤的影响。如亚G1期含量增加和集落形成减少所示，沉默p53R2增强了电离辐射和阿霉素处理的凋亡效应。这种增敏效应是DNA损伤剂特有的。彗星试验和γ-H2AX磷酸化状态表明，p53R2水平降低会抑制DNA修复。沉默p53R2还在转录后水平降低了p21（WAF1/CIP1）的水平，提示p53依赖的DNA修复和细胞周期阻滞途径之间存在联系。使用稳定表达显性负性突变型p53的LNCaP亚系，我们发现p53R2沉默的增敏效应是由p53依赖的凋亡途径介导的。在诱导p53依赖凋亡存在缺陷的LNCaP亚系（R273H、R248W和G245S）中，p53R2沉默并未增强DNA损伤诱导的凋亡，而p53R2沉默在保留诱导p53依赖凋亡能力的LNCaP亚系（P151S）中是有效的。本研究表明，p53R2是一个潜在的治疗靶点，可用于提高一部分前列腺癌患者电离辐射或DNA损伤化疗的疗效。
