PDF(Pubmed)
Abstract：
Indoleamine-2, 3-dioxygenase (IDO1) and Tryptophan-2, 3-dioxygenase (TDO) catalyze the conversion of L-tryptophan to N-formyl-kynurenine and thus play primary roles in metabolism, inflammation, and tumor immune surveillance. Because their activities depend on their heme contents, which vary in biological settings and go up or down in a dynamic manner, we studied how their heme levels may be impacted by nitric oxide (NO) in mammalian cells. We utilized cells expressing TDO or IDO1 either naturally or via transfection and determined their activities, heme contents, and expression levels as a function of NO exposure. We found NO has a bimodal effect: a narrow range of low NO exposure promoted cells to allocate heme into the heme-free TDO and IDO1 populations and consequently boosted their heme contents and activities 4- to 6-fold, while beyond this range the NO exposure transitioned to have a negative impact on their heme contents and activities. NO did not alter dioxygenase protein expression levels, and its bimodal impact was observed when NO was released by a chemical donor or was generated naturally by immune-stimulated macrophage cells. NO-driven heme allocations to IDO1 and TDO required participation of a GAPDH-heme complex and for IDO1 required chaperone Hsp90 activity. Thus, cells can up- or downregulate their IDO1 and TDO activities through a bimodal control of heme allocation by NO. This mechanism has important biomedical implications and helps explain why the IDO1 and TDO activities in animals go up and down in response to immune stimulation.
摘要：
吲哚胺-2，3-双加氧酶（IDO1）和色氨酸-2，3-双加氧酶（TDO）催化L-色氨酸转化为N-甲酰-犬尿氨酸，因此在代谢中起主要作用，炎症,和肿瘤免疫监视。因为它们的活动取决于血红素含量，它们在生物学环境中有所不同，并以动态的方式上升或下降，我们研究了哺乳动物细胞中血红素水平如何受到一氧化氮（NO）的影响。我们利用天然或通过转染表达TDO或IDO1的细胞，并确定其活性，血红素含量,和表达水平作为NO暴露的函数。我们发现NO具有双峰效应：狭窄范围的低NO暴露促进细胞将血红素分配到无血红素的TDO和IDO1群体中，从而提高其血红素含量和活性4至6倍，尽管超出此范围，但NO暴露会对其血红素含量和活性产生负面影响。NO没有改变双加氧酶蛋白表达水平，当NO由化学供体释放或由免疫刺激的巨噬细胞自然产生时，观察到其双峰影响。NO驱动的血红素分配给IDO1和TDO需要GAPDH-血红素复合物的参与，而IDO1则需要伴侣Hsp90活性。因此，细胞可以通过NO对血红素分配的双峰控制来上调或下调其IDO1和TDO活性。这种机制具有重要的生物医学意义，并有助于解释为什么动物中的IDO1和TDO活性随着免疫刺激而上升和下降。
