GAMMA INTERFERON REGULATION OF VITAMIN D ACTION

伽玛干扰素对维生素 D 作用的调节

• 批准号: 6375110
• 负责人: ADRIANA Silvia DUSSO
• 金额: $ 14.77万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-30 至 2003-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6375110
• 关键词: 1,25 dihydroxycholecalciferol; enzyme activity; enzyme mechanism; gene induction /repression; gene targeting; genetic transcription; interferon gamma; laboratory mouse; oxygenases; protein protein interaction; steroid hormone metabolism; tissue /cell culture; transcription factor; vitamin D receptors

1,25-dihydroxyvitamin D [1,25D], the hormonal form of vitamin D is a potent regulator of calcium homeostasis. To maintain normal serum calcium, 1,25D tightly controls its own serum levels by suppressing renal and extrarenal 1alpha-hydroxylases and by inducing 24-hydroxylase. In sarcoidosis and tuberculosis, the capacity of 1,25D to regulate its synthesis and degradation is lost. This phenomenon can be reproduced in vitro by exposing normal human macrophages to gamma-interferon (gamma-IFN). Gamma- IFN markedly enhances 1,25(OH)2D3 production but antagonizes 1,25D regulation of 1alpha- and 24-hydroxylases. Clearly, gamma- IFN impairs 1,25D control of its own synthesis and catabolism. To clarify the mechanisms mediating gamma-IFN inhibition of 1,25D action, we utilized the human monocytic cell line THP-1. THP-1 cells mimic human macrophages in 1,25D synthesis and in the regulation of 1alpha- and 24-hydroxylases in response to 1,25D and gamma-IFN. We focused on 1,25D induction of 24-hydroxylase. In THP-1 cells and normal monocytes, gamma-IFN impairs 1,25D induction of 24-hydroxylase mRNA. Gamma-IFN does not affect either the binding of 1,25D to the vitamin D receptor (VDR) or the stability of the 24-hydroxylase mRNA suggesting that gamma- IFN may directly impair 1,25D-induction of 24-hydroxylase gene transcription. Most responses to gamma-IFN require Stat1 activation. Gamma-IFN binding to its receptor activates Janus kinases to tyrosine phosphorylate Stat1. Stat1 then homodimerizes and translocates to the nucleus where it interacts directly with a gamma-IFN activation sequence and with the nuclear co-activators CBP/p300 to regulate transcription. Recent studies, however, demonstrate gamma-IFN transcriptional activation through Stat1 independent pathways. To induce 24- hydroxylase expression, 1,25 binds to cytosolic VDR, which translocates to the nucleus and heterodimerizes with the retinoid X receptor (RXR). VDR/RXR interactions with both vitamin D responsive elements (VDREs) in the human 24-hydroxylase promoter and nuclear receptor co-activators enhance gene transcription. In THP-1 cells, gamma-IFN impairs VDR/RXR binding to both VDREs through interactions of active Stat1 with the VDR/RXR, and reduces 1,25D-transcriptional activity at the VDRE. We hypothesize, therefore, that gamma-IFN activation of Stat1 (or a Stat1 like protein) antagonizes 1,25D induction of 24-hydroxylase through both interactions with the VDR/RXR that impair VDRE binding and competition with the VDR/RXR for essential nuclear coactivators. Also, gamma-IFN antagonism on 1,25D transcriptional activity causes abnormal 1,25D homeostasis in inflammatory processes. To test these hypotheses, we propose to examine: (1) The contribution of JAK-Stat1 and/or Stat1- independent pathways to the inhibitory effects of gamma-IFN on 1,25D induction of 24-hydroxylase gene transcription; (2) gamma- IFN antagonism on protein-protein and protein-DNA interactions of VDR/RXR critical in 1,25D transcriptional activity; (3) gamma- IFN/1,25D antagonism on 1alpha-hydroxylase expression.

1,25-二羟基维生素D [1,25d]，维生素D的激素形式是钙稳态的有效调节剂。 为了维持正常的血清钙，1,25D通过抑制肾脏和外1α-羟基酶和诱导24-羟化酶来严格控制自己的血清水平。 在结节症和结核病中，调节其合成和降解的1,25D的能力消失了。 可以通过将正常的人类巨噬细胞暴露于伽马 - 互化（伽马-IFN）的情况下在体外重现这种现象。 γ-IFN显着增强了1,25（OH）2d3的产生，但对1,25d的1α-和24-羟基酶进行了拮抗。 显然，伽马ifn会损害1,25D对其自身合成和分解代谢的控制。为了阐明介导γ-IFN抑制1,25D作用的机制，我们利用了人类单核细胞系THP-1。 THP-1细胞模仿1,25D合成中的人类巨噬细胞，以及对1,25D和γ-IFN的1α-和24-羟化酶的调节。 我们专注于1,25D诱导24-羟化酶。在THP-1细胞和正常的单核细胞中，γ-IFN损害了1,25d诱导24-羟化酶mRNA。 γ-IFN不会影响1,25D与维生素D受体（VDR）的结合，也不会影响24-羟化酶mRNA的稳定性，这表明γ-IFN可能直接损害1,25D诱导24-羟化酶基因转录的1,25D诱导。 对γ-IFN的大多数响应都需要STAT1激活。 γ-IFN与其受体结合激活Janus激酶与酪氨酸磷酸化STAT1。 STAT1然后均二聚并易位到核直接与γ-IFN激活序列相互作用，并与核共激活器CBP/p300相互作用以调节转录。 然而，最近的研究表明，通过STAT1独立途径，γ-IFN转录激活。 为了诱导24-羟化酶表达，1,25与胞质VDR结合，胞质VDR易位到细胞核并与类视钉X受体（RXR）异二聚体。 VDR/RXR与人24-羟化酶启动子和核受体共激活剂中维生素D反应元件（VDR）的相互作用增强了基因转录。在THP-1细胞中，γ-IFN通过活性STAT1与VDR/RXR的相互作用而损害了VDR/RXR与这两种VDR的结合，并减少了VDRE处的1,25D转录活性。 因此，我们假设STAT1的γ-IFN激活（或类似STAT1的蛋白质）通过与VDR/RXR的两种相互作用来拮抗24-羟化酶的1,25D诱导VDR/RXR，从而损害了VDRE的结合，并损害了VDR的结合，并且与基本核共振剂的VDR/RXR竞争。 此外，对1,25D转录活性的γ-IFN拮抗作用在炎症过程中导致1,25d稳态异常。 为了检验这些假设，我们建议检查：（1）JAK-STAT1和/或STAT1-独立途径对γ-IFN抑制作用对1,25D诱导24-羟化酶基因转录的抑制作用的贡献； （2）在1,25D转录活性中，VDR/RXR的蛋白质 - 蛋白质和蛋白-DNA相互作用的γ-IFN拮抗作用； （3）对1alpha-羟化酶表达的γ-IFN/1,25D拮抗作用。