Cyclooxygenase-2 suppresses hypoxia-induced apoptosis via a combination of direct and indirect inhibition of p53 activity in a human prostate cancer cell line
Cyclooxygenase-2 suppresses hypoxia-induced apoptosis via a combination of direct and indirect inhibition of p53 activity in a human prostate cancer cell line
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DOI：
10.1074/jbc.m406577200
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发表时间：
2005-02-04
影响因子：
4.8
通讯作者：
Levine, AC
中科院分区：
文献类型：
--
作者：
Liu, XH;Kirschenbaum, A;Levine, AC
虽然p53失活突变已在大多数人类癌症中被描述，但它们在前列腺癌中的作用是有争议的，因为突变是罕见的，特别是在早期病变中。p53被缺氧和其他应激物激活，主要由Mdm 2蛋白调节。环氧合酶（考克斯）-2是一种诱导型酶，催化花生四烯酸转化为花生四烯酸和其他类花生酸，也可被缺氧诱导。考克斯-2和产生的异黄酮增加肿瘤细胞增殖、抗凋亡和血管生成。以前的报道表明p53和考克斯-2之间存在复杂的相互关系。为了阐明考克斯-2对p53在缺氧反应中的作用，我们将考克斯-2基因转染p53阳性、考克斯-2阴性的人前列腺癌细胞系MDA-PCa-2b。在常氧和低氧条件下比较考克斯-2（+）和考克斯-2（-）细胞中功能性p53和Mdm 2的表达。我们的研究结果表明，缺氧增加考克斯-2蛋白水平和p53转录活性在这些细胞。考克斯-2的强制表达增加了肿瘤细胞的生存力，减少了对缺氧的细胞凋亡。考克斯-2（+）细胞在常氧或缺氧条件下Mdm 2磷酸化水平均增加。过表达考克斯-2可抑制缺氧诱导的p53磷酸化，促进p53与Mdm 2蛋白的结合。此外，考克斯-2表达细胞表现出减少缺氧诱导的p53蛋白的核积聚。最后，强制表达的考克斯-2抑制基础和缺氧诱导的p53转录活性，这种效果是模仿加入PGE，野生型细胞。这些结果表明，考克斯-2通过直接作用和间接调节Mdm 2活性在抑制缺氧诱导的p53活性中起作用。这些数据表明，即使在野生型p53存在下，考克斯-2阳性前列腺癌细胞也可能具有受损的p53功能，并且这些细胞中的p53活性可以通过抑制考克斯-2活性而恢复。
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 PGE, 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.