Petris Michael J, Smith Kathryn, Lee Jaekwon, Thiele Dennis J
Department of Nutritional Sciences, University of Missouri, Columbia, Missouri 65211, USA.
J Biol Chem. 2003 Mar 14;278(11):9639-46. doi: 10.1074/jbc.M209455200. Epub 2002 Dec 25.
Copper uptake at the plasma membrane and subsequent delivery to copper-dependent enzymes is essential for many cellular processes, including mitochondrial oxidative phosphorylation, free radical detoxification, pigmentation, neurotransmitter synthesis, and iron metabolism. However, intracellular levels of this nutrient must be controlled because it is potentially toxic in excess concentrations. The hCtr1 protein functions in high affinity copper uptake at the plasma membrane of human cells. In this study, we demonstrate that levels of the hCtr1 protein at the plasma membrane of HEK293 cells were reduced when cells were exposed to elevated copper. This decrease in surface hCtr1 levels was associated with an increased rate of endocytosis, and low micromolar concentrations of copper were sufficient to stimulate this process. Inhibitors of clathrin-dependent endocytosis prevented the trafficking of hCtr1 from the plasma membrane, and newly internalized hCtr1 and transferrin were co-localized. Significantly, elevated copper concentrations also resulted in the degradation of the hCtr1 protein. Our findings suggest that hCtr1-mediated copper uptake into mammalian cells is regulated by a post-translational mechanism involving copper-stimulated endocytosis and degradation of the transporter.
铜在质膜上的摄取以及随后向铜依赖性酶的传递对于许多细胞过程至关重要，包括线粒体氧化磷酸化、自由基解毒、色素沉着、神经递质合成和铁代谢。然而，这种营养素的细胞内水平必须受到控制，因为其浓度过高时具有潜在毒性。hCtr1蛋白在人类细胞质膜上的高亲和力铜摄取中发挥作用。在本研究中，我们证明当细胞暴露于升高的铜时，HEK293细胞质膜上的hCtr1蛋白水平降低。表面hCtr1水平的这种降低与内吞作用速率增加有关，低微摩尔浓度的铜就足以刺激这一过程。网格蛋白依赖性内吞作用的抑制剂阻止了hCtr1从质膜的运输，并且新内化的hCtr1和转铁蛋白共定位。值得注意的是，升高的铜浓度还导致hCtr1蛋白的降解。我们的研究结果表明，hCtr1介导的铜摄取进入哺乳动物细胞受一种翻译后机制调节，该机制涉及铜刺激的内吞作用和转运蛋白的降解。
