Liu Xin-Hua, Kirschenbaum Alexander, Yu Kang, Yao Shen, Levine Alice C
Department of Medicine, Division of Endocrinology and Metabolism, and Urology, Mount Sinai School of Medicine, New York, New York 10029, USA.
J Biol Chem. 2005 Feb 4;280(5):3817-23. doi: 10.1074/jbc.M406577200. Epub 2004 Nov 18.
Although p53-inactivating mutations have been described in the majority of human cancers, their role in prostate cancer is controversial as mutations are uncommon, particularly in early lesions. p53 is activated by hypoxia and other stressors and is primarily regulated by the Mdm2 protein. Cyclooxygenase (COX)-2, an inducible enzyme that catalyzes the conversion of arachidonic acid to prostaglandins and other eicosanoids, is also induced by hypoxia. COX-2 and resultant prostaglandins increase tumor cell proliferation, resistance to apoptosis, and angiogenesis. Previous reports indicate a complex, reciprocal relationship between p53 and COX-2. To elucidate the effects of COX-2 on p53 in response to hypoxia, we transfected the COX-2 gene into the p53-positive, COX-2-negative MDA-PCa-2b human prostate cancer cell line. The expression of functional p53 and Mdm2 was compared in COX-2+ versus COX-2- cells under normoxic and hypoxic conditions. Our results demonstrated that hypoxia increases both COX-2 protein levels and p53 transcriptional activity in these cells. Forced expression of COX-2 increased tumor cell viability and decreased apoptosis in response to hypoxia. COX-2+ cells had increased Mdm2 phosphorylation in either normoxic or hypoxic conditions. Overexpression of COX-2 abrogated hypoxia-induced p53 phosphorylation and promoted the binding of p53 to Mdm2 protein in hypoxic cells. In addition, COX-2-expressing cells exhibited decreased hypoxia-induced nuclear accumulation of p53 protein. Finally, forced expression of COX-2 suppressed both basal and hypoxia-induced p53 transcriptional activity, and this effect was mimicked by the addition of PGE2 to wild-type cells. These results demonstrated a role for COX-2 in the suppression of hypoxia-induced p53 activity via both direct effects and indirect modulation of Mdm2 activity. These data imply that COX-2-positive prostate cancer cells can have impaired p53 function even in the presence of wild-type p53 and that p53 activity can be restored in these cells via inhibition of COX-2 activity.
虽然在大多数人类癌症中都发现了使p53失活的突变，但它们在前列腺癌中的作用仍存在争议，因为突变并不常见，尤其是在早期病变中。p53可被缺氧及其他应激源激活，且主要受Mdm2蛋白调控。环氧化酶（COX）-2是一种诱导性酶，可催化花生四烯酸转化为前列腺素和其他类二十烷酸，它也可被缺氧诱导。COX-2及由此产生的前列腺素会增加肿瘤细胞增殖、抗凋亡能力及血管生成。先前的报道表明p53与COX-2之间存在复杂的相互关系。为了阐明COX-2在缺氧条件下对p53的影响，我们将COX-2基因转染到p53阳性、COX-2阴性的MDA-PCa-2b人前列腺癌细胞系中。在常氧和缺氧条件下，比较了COX-2阳性细胞与COX-2阴性细胞中功能性p53和Mdm2的表达。我们的结果表明，缺氧会增加这些细胞中COX-2蛋白水平和p53转录活性。COX-2的强制表达增加了肿瘤细胞活力，并降低了缺氧诱导的细胞凋亡。在常氧或缺氧条件下，COX-2阳性细胞的Mdm2磷酸化增加。COX-2的过表达消除了缺氧诱导的p53磷酸化，并促进了缺氧细胞中p53与Mdm2蛋白的结合。此外，表达COX-2的细胞表现出缺氧诱导的p53蛋白核积累减少。最后，COX-2的强制表达抑制了基础和缺氧诱导的p53转录活性，并且向野生型细胞中添加前列腺素E2可模拟这种效应。这些结果证明了COX-2在通过直接作用和间接调节Mdm2活性来抑制缺氧诱导的p53活性中所起的作用。这些数据表明，COX-2阳性的前列腺癌细胞即使在存在野生型p53的情况下也可能存在p53功能受损，并且通过抑制COX-2活性可恢复这些细胞中的p53活性。
