Jackson M W, Lindstrom M S, Berberich S J
Department of Oncology-Pathology, Cancer Center Karolinska, Karolinska Institutet and Hospital, S-171 76 Stockholm, Sweden.
J Biol Chem. 2001 Jul 6;276(27):25336-41. doi: 10.1074/jbc.M010685200. Epub 2001 Apr 10.
Regulation of p53 involves a complex network of protein interactions. The primary regulator of p53 protein stability is the Mdm2 protein. ARF and MdmX are two proteins that have recently been shown to inhibit Mdm2-mediated degradation of p53 via distinct associations with Mdm2. We demonstrate here that ARF is capable of interacting with MdmX and in a manner similar to its association with Mdm2, sequestering MdmX within the nucleolus. The sequestration of MdmX by ARF results in an increase in p53 transactivation. In addition, the redistribution of MdmX by ARF requires that a nucleolar localization signal be present on MdmX. Although expression of either MdmX or ARF leads to Mdm2 stabilization, coexpression of both MdmX and ARF results in a decrease in Mdm2 protein levels. Similarly, increasing ARF protein levels in the presence of constant MdmX and Mdm2 leads to a dose-dependent decrease in Mdm2 levels. Under these conditions, ARF can synergistically reverse the ability of Mdm2 and MdmX to inhibit p53-dependent transactivation. Finally, the association and redistribution of MdmX by ARF has no effect on the protein stability of either ARF or MdmX. Taken together, these results demonstrate that the interaction between MdmX and ARF represents a novel pathway for regulating Mdm2 protein levels. Additionally, both MdmX and Mdm2, either individually or together, are capable of antagonizing the effects of the ARF tumor suppressor on p53 activity.
p53的调控涉及一个复杂的蛋白质相互作用网络。p53蛋白稳定性的主要调节因子是Mdm2蛋白。ARF和MdmX是最近被证明通过与Mdm2的不同结合来抑制Mdm2介导的p53降解的两种蛋白质。我们在此证明，ARF能够与MdmX相互作用，并且以类似于其与Mdm2结合的方式，将MdmX隔离在核仁内。ARF对MdmX的隔离导致p53反式激活增加。此外，ARF对MdmX的重新分布要求MdmX上存在核仁定位信号。尽管MdmX或ARF的表达都会导致Mdm2稳定，但MdmX和ARF的共表达会导致Mdm2蛋白水平降低。同样，在MdmX和Mdm2恒定的情况下增加ARF蛋白水平会导致Mdm2水平呈剂量依赖性降低。在这些条件下，ARF可以协同逆转Mdm2和MdmX抑制p53依赖性反式激活的能力。最后，ARF对MdmX的结合和重新分布对ARF或MdmX的蛋白质稳定性没有影响。综上所述，这些结果表明MdmX和ARF之间的相互作用代表了一种调节Mdm2蛋白水平的新途径。此外，MdmX和Mdm2单独或共同都能够拮抗ARF肿瘤抑制因子对p53活性的影响。
