Clinical Brain Disorders Branch, Genes, Cognition, and Psychosis Program, NIMH, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 2011 Oct 7;286(40):34752-60. doi: 10.1074/jbc.M111.262790. Epub 2011 Aug 16.
Catechol-O-methyltransferase (COMT) is a key enzyme for inactivation and metabolism of catechols, including dopamine, norepinephrine, caffeine, and estrogens. It plays an important role in cognition, arousal, pain sensitivity, and stress reactivity in humans and in animal models. The human COMT gene is associated with a diverse spectrum of human behaviors and diseases from cognition and psychiatric disorders to chronic pain and cancer. There are two major forms of COMT proteins, membrane-bound (MB) COMT and soluble (S) COMT. MB-COMT is the main form in the brain. The cellular distribution of MB-COMT in cortical neurons remains unclear and the orientation of MB-COMT on the cellular membrane is controversial. In this study, we demonstrate that MB-COMT is located in the cell body and in axons and dendrites of rat cortical neurons. Analyses of MB-COMT orientation with computer simulation, flow cytometry and a cell surface enzyme assay reveal that the C-terminal catalytic domain of MB-COMT is in the extracellular space, which suggests that MB-COMT can inactivate synaptic and extrasynaptic dopamine on the surface of presynaptic and postsynaptic neurons. Finally, we show that the COMT inhibitor tolcapone induces cell death via the mechanism of apoptosis, and its cytotoxicity is dependent on dosage and correlated with COMT Val/Met genotypes in human lymphoblastoid cells. These results suggest that MB-COMT specific inhibitors can be developed and that tolcapone may be less hazardous at low doses and in specific genetic backgrounds.
儿茶酚-O-甲基转移酶（COMT）是儿茶酚类物质（包括多巴胺、去甲肾上腺素、咖啡因和雌激素）失活和代谢的关键酶。它在人类和动物模型的认知、觉醒、疼痛敏感性和应激反应中起着重要作用。人类 COMT 基因与从认知和精神障碍到慢性疼痛和癌症等各种人类行为和疾病有关。COMT 蛋白有两种主要形式，即膜结合（MB）COMT 和可溶性（S）COMT。MB-COMT 是大脑中的主要形式。MB-COMT 在皮质神经元中的细胞分布尚不清楚，其在细胞膜上的取向也存在争议。在这项研究中，我们证明 MB-COMT 位于大鼠皮质神经元的细胞体和轴突及树突中。通过计算机模拟、流式细胞术和细胞表面酶测定分析 MB-COMT 取向表明，MB-COMT 的 C 端催化结构域位于细胞外空间，这表明 MB-COMT 可以在突触前和突触后神经元表面失活突触和细胞外多巴胺。最后，我们发现 COMT 抑制剂托卡朋通过细胞凋亡机制诱导细胞死亡，其细胞毒性取决于剂量，并与人淋巴母细胞系中的 COMT Val/Met 基因型相关。这些结果表明，可以开发针对 MB-COMT 的特异性抑制剂，并且托卡朋在低剂量和特定遗传背景下可能危害较小。
