Naturally Occurring Eccentric Cleavage Products of Provitamin A β-Carotene Function as Antagonists of Retinoic Acid Receptors
Naturally Occurring Eccentric Cleavage Products of Provitamin A β-Carotene Function as Antagonists of Retinoic Acid Receptors
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DOI：
10.1074/jbc.m111.325142
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发表时间：
2012-05-04
影响因子：
4.8
通讯作者：
Harrison, Earl H.
中科院分区：
文献类型：
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作者：
Eroglu, Abdulkerim;Hruszkewycz, Damian P.;Harrison, Earl H.
β-胡萝卜素是维生素原A的主要膳食来源。由β-胡萝卜素加氧酶1催化的β-胡萝卜素的中心裂解产生两个分子的视黄醇。随后的氧化产生全反式视黄酸（ATRA），其作为核转录因子家族视黄酸受体（RAR）的配体发挥作用。β-胡萝卜素在非中心双键处的偏心裂解由其他酶催化，并且也可以非酶促地发生。这些反应的产物是β-脱胡萝卜素醛和β-脱胡萝卜素酮，它们在哺乳动物中的生物学功能尚不清楚。我们使用报告基因分析表明，没有β-脱辅基类胡萝卜素显着激活RAR。然而，重要的是，β-apo-14 '-胡萝卜素醛、β-apo-14'-胡萝卜素酸和β-apo-13-胡萝卜素酮拮抗ATRA诱导的RAR反式激活。竞争性放射性配体结合试验表明，这些推定的RAR拮抗剂竞争直接与视黄酸高亲和力结合纯化的受体。分子模拟研究证实，β-载脂蛋白-13-胡萝卜素酮可以直接与类维生素A受体的配体结合位点相互作用。β-载脂蛋白-13-胡萝卜素酮和β-载脂蛋白-14 '-类胡萝卜素抑制Hep G2细胞中ATRA诱导的类维生素A应答基因的表达。最后，我们开发了LC/MS方法，发现人血浆中存在3-5 nM的β-apo-13-胡萝卜素酮。这些发现表明，β-脱辅基类胡萝卜素的功能作为天然存在的类维生素A拮抗剂。这些代谢物对类维生素A信号传导的拮抗作用可能对膳食β-胡萝卜素作为维生素A原和作为心血管疾病和癌症风险调节剂的活性有影响。
beta-Carotene is the major dietary source of provitamin A. Central cleavage of beta-carotene catalyzed by beta-carotene oxygenase 1 yields two molecules of retinaldehyde. Subsequent oxidation produces all-trans-retinoic acid (ATRA), which functions as a ligand for a family of nuclear transcription factors, the retinoic acid receptors (RARs). Eccentric cleavage of beta-carotene at non-central double bonds is catalyzed by other enzymes and can also occur non-enzymatically. The products of these reactions are beta-apocarotenals and beta-apocarotenones, whose biological functions in mammals are unknown. We used reporter gene assays to show that none of the beta-apocarotenoids significantly activated RARs. Importantly, however, beta-apo-14'-carotenal, beta-apo-14'-carotenoic acid, and beta-apo-13-carotenone antagonized ATRA-induced transactivation of RARs. Competitive radioligand binding assays demonstrated that these putative RAR antagonists compete directly with retinoic acid for high affinity binding to purified receptors. Molecular modeling studies confirmed that beta-apo-13-carotenone can interact directly with the ligand binding site of the retinoid receptors. beta-Apo-13-carotenone and the beta-apo-14'-carotenoids inhibited ATRA-induced expression of retinoid responsive genes in Hep G2 cells. Finally, we developed an LC/MS method and found 3-5 nM beta-apo-13-carotenone was present in human plasma. These findings suggest that beta-apocarotenoids function as naturally occurring retinoid antagonists. The antagonism of retinoid signaling by these metabolites may have implications for the activities of dietary beta-carotene as a provitamin A and as a modulator of risk for cardiovascular disease and cancer.