Li X S, Rishi A K, Shao Z M, Dawson M I, Jong L, Shroot B, Reichert U, Ordonez J, Fontana J A
Department of Medicine, University of Maryland Cancer Center, Baltimore 21201, USA.
Cancer Res. 1996 Nov 1;56(21):5055-62.
p21WAF1/CIP1 plays a major role in the induction of G1 arrest following DNA damage. Although p21WAF1/CIP1 expression is regulated by the tumor suppressor p53, induction of p21WAF1/CIP1 expression through p53-independent pathways has been described in numerous cell types. In this report, we describe the mechanism by which the retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) induces p21WAF1/CIP1 in breast carcinoma cells possessing either a wild-type (MCF-7 cells) or mutated (MDA-MB-468 cells) p53. Exposure of MDA-MB-468 cells to this retinoid results in an approximately 10-fold increase in p21WAF1/CIP1 mRNA levels, whereas less than a 2-fold increase in p21WAF1/CIP1 gene transcription was observed as indicated by transient transfection experiments utilizing a p21WAF1/CIP1 promoter firefly luciferase reporter gene construct and nuclear run-off studies. We found similar results in the MCF-7 cells (Z-M. Shao et al., Oncogene, 11: 493-504, 1995). We have now found that while enhancing p21WAF1/CIP1 gene transcription minimally, this retinoid increases p21WAF1/CIP1 mRNA stability by 3-fold in both cell types. We also demonstrate that approximately 1.5 kb of the 3' untranslated region causes enhanced instability of p21WAF1/CIP1 mRNA. The retinoid-dependent increase in p21WAF1/CIP1 mRNA stability is accompanied by an increase in p21WAF1/CIP1 protein expression, as indicated by Western blot experiments utilizing anti-p21WAF1/CIP1 monoclonal antibody. This increase in p21WAF1/CIP1 is subsequently followed by the onset of programmed cell death in both cell types. Thus, CD437 is a novel retinoid which enhances p21WAF1/CIP1 mRNA levels through stabilization of the message regardless of the p53 status of the cell.
p21WAF1/CIP1在DNA损伤后诱导G1期阻滞过程中起主要作用。尽管p21WAF1/CIP1的表达受肿瘤抑制因子p53调控，但在多种细胞类型中已发现通过p53非依赖途径诱导p21WAF1/CIP1表达的情况。在本报告中，我们描述了维甲酸6-[3-(1-金刚烷基)-4-羟基苯基]-2-萘甲酸（CD437）在具有野生型（MCF-7细胞）或突变型（MDA-MB-468细胞）p53的乳腺癌细胞中诱导p21WAF1/CIP1的机制。将MDA-MB-468细胞暴露于这种维甲酸后，p21WAF1/CIP1 mRNA水平增加约10倍，而利用p21WAF1/CIP1启动子萤火虫荧光素酶报告基因构建体和细胞核转录实验表明，p21WAF1/CIP1基因转录增加不到2倍。我们在MCF-7细胞中也得到了类似结果（Z-M.邵等人，《癌基因》，11: 493 - 504，1995）。我们现在发现，这种维甲酸虽然对p21WAF1/CIP1基因转录的增强作用极小，但在两种细胞类型中都使p21WAF1/CIP1 mRNA稳定性提高了3倍。我们还证明，3'非翻译区约1.5 kb的片段会导致p21WAF1/CIP1 mRNA稳定性增强。如利用抗p21WAF1/CIP1单克隆抗体进行的蛋白质印迹实验所示，维甲酸依赖性地增加p21WAF1/CIP1 mRNA稳定性伴随着p21WAF1/CIP1蛋白表达增加。p21WAF1/CIP1的这种增加随后在两种细胞类型中都引发程序性细胞死亡。因此，CD437是一种新型维甲酸，无论细胞的p53状态如何，它都通过稳定信使RNA来提高p21WAF1/CIP1 mRNA水平。
