Chen Delin, Li Muyang, Luo Jianyuan, Gu Wei
Institute for Cancer Genetics, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA.
J Biol Chem. 2003 Apr 18;278(16):13595-8. doi: 10.1074/jbc.C200694200. Epub 2003 Feb 26.
The p53 tumor suppressor is maintained at low levels in normal cells by Mdm2-mediated degradation and strongly stabilized in response to various types of stress including hypoxia. Although hypoxia-inducible factor 1 alpha (HIF-1 alpha) has been implicated to be involved in p53 stabilization, the precise mechanism by which HIF-1 alpha regulates p53-mediated function remains unknown. Here, we found that HIF-1 alpha directly binds Mdm2 both in vitro and in vivo; in contrast, p53 fails to directly interact with HIF-1 alpha in vitro. Interestingly, Mdm2 expression can significantly enhance the in vivo association between p53 and HIF-1 alpha, indicating that Mdm2 may act as a bridge and mediate the indirect interaction between HIF-1 alpha and p53 in cells. Furthermore, HIF-1 alpha protects p53 degradation mediated by Mdm2, and leads to activation of p53-mediated transcription in cells. To elucidate the mechanism of HIF-1 alpha-mediated effect, we also found that HIF-1 alpha can significantly suppress Mdm2-mediated p53 ubiquitination in vitro and blocks Mdm2-mediated nuclear export of p53. These results have significant implications regarding the molecular mechanism by which p53 is activated by HIF-1 alpha in response to hypoxia.
p53肿瘤抑制因子在正常细胞中通过Mdm2介导的降解维持在低水平，并在包括缺氧在内的各种应激反应中强烈稳定。尽管缺氧诱导因子1α（HIF-1α）被认为参与p53的稳定，但HIF-1α调节p53介导功能的精确机制仍不清楚。在这里，我们发现HIF-1α在体外和体内都直接与Mdm2结合；相反，p53在体外不能直接与HIF-1α相互作用。有趣的是，Mdm2的表达可以显著增强p53与HIF-1α在体内的结合，表明Mdm2可能作为桥梁介导细胞中HIF-1α与p53之间的间接相互作用。此外，HIF-1α保护p53免受Mdm2介导的降解，并导致细胞中p53介导的转录激活。为了阐明HIF-1α介导作用的机制，我们还发现HIF-1α在体外可以显著抑制Mdm2介导的p53泛素化，并阻止Mdm2介导的p53核输出。这些结果对于缺氧时HIF-1α激活p53的分子机制具有重要意义。
