IRON REGULATES THE INTRACELLULAR DEGRADATION OF IRON REGULATORY PROTEIN-2 BY THE PROTEASOME
IRON REGULATES THE INTRACELLULAR DEGRADATION OF IRON REGULATORY PROTEIN-2 BY THE PROTEASOME
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DOI：
10.1074/jbc.270.37.21645
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发表时间：
1995-09-15
影响因子：
4.8
通讯作者：
LEIBOLD, EA
中科院分区：
文献类型：
--
作者：
GUO, B;PHILLIPS, JD;LEIBOLD, EA
铁调节蛋白（IRP1 和 IRP2）是 RNA 结合蛋白，可与称为铁反应元件 (IRE) 的特定结构结合，这些结构位于 mRNA 的 5'- 或 3'- 非翻译区，编码参与铁稳态的蛋白质。 IRP1和IRP2 RNA结合活性受铁调节； IRP1 和 IRP2 在铁耗尽的细胞中以高亲和力结合 IRE，而在铁充足的细胞中以低亲和力结合。 IRP1 RNA 结合活性的降低是通过脱辅基蛋白和 4Fe-4S 形式之间的转换而发生的，IRP1 水平没有变化，而 IRP2 RNA 结合活性的降低反映了 IRP2 水平的降低。为了确定铁降低 IRP2 水平的机制，我们研究了铁在大鼠肝癌和人 HeLa 细胞中对 IRP2 的调节。 IRP2 水平的铁依赖性降低并不是由于 IRP2 mRNA 量的减少或 IRP2 合成速率的降低。脉冲追踪实验表明，铁会使 IRP2 的降解率增加 3 倍。 IRP2 降解取决于蛋白质合成，而不是转录，这表明需要不稳定的蛋白质。 IRP2 降解不能被溶酶体抑制剂或钙蛋白酶 II 抑制剂阻止，但可以被阻断蛋白酶体功能的抑制剂阻止。这些数据表明蛋白酶体参与铁介导的 IRP2 蛋白水解。
Iron regulatory proteins (IRP1 and IRP2) are RNA-binding proteins that bind to specific structures, termed iron responsive elements (IREs), that are located in the 5'- or 3'-untranslated regions of mRNAs that encode proteins involved in iron homeostasis. IRP1 and IRP2 RNA binding activities are regulated by iron; IRP1 and IRP2 bind IREs with high affinity in iron-depleted cells and with low affinity in iron-repleted cells. The decrease in IRP1 RNA binding activity occurs by a switch between apoprotein and 4Fe-4S forms, without changes in IRP1 levels, whereas the decrease in IRP2 RNA binding activity reflects a reduction in IRP2 levels. To determine the mechanism by which iron decreases IRP2 levels, we studied IRP2 regulation by iron in rat hepatoma and human HeLa cells. The iron-dependent decrease in IRP2 levels was not due to a decrease in the amount of IRP2 mRNA or to a decrease in the rate of IRP2 synthesis. Pulse chase experiments demonstrated that iron resulted in a 3-fold increase in the degradation rate of IRP2. IRP2 degradation depends on protein synthesis, but not transcription, suggesting a requirement for a labile protein. IRP2 degradation is not prevented by lysosomal inhibitors or calpain II inhibitors, but is prevented by inhibitors that block proteasome function. These data suggest the involvement of the proteasome in iron-mediated IRP2 proteolysis.