Martínez-Campa C, Alonso-González C, Mediavilla M D, Cos S, González A, Ramos S, Sánchez-Barceló E J
Department of Physiology and Pharmacology, School of Medicine, University of Cantabria, Santander, Spain.
J Pineal Res. 2006 May;40(4):291-6. doi: 10.1111/j.1600-079X.2006.00315.x.
Cadmium (Cd) is a heavy metal affecting human health both through environmental and occupational exposure. There is evidence that Cd accumulates in several organs and is carcinogenic to humans. In vivo, Cd mimics the effect of estrogens in the uterus and mammary gland. In estrogen-responsive breast cancer cell lines, Cd stimulates proliferation and can also activate the estrogen receptor independent of estradiol. The ability of this metalloestrogen to increase gene expression in MCF7 cells is blocked by anti-estrogens suggesting that the activity of these compounds is mediated by ER alpha. The aims of this work were to test whether melatonin inhibits Cd-induced proliferation in MCF7 cells, and also to study whether melatonin specifically inhibits Cd-induced ER alpha transactivation. We show that melatonin prevents the Cd-induced growth of synchronized MCF7 breast cancer cells. In transient transfection experiments, we prove that both ER alpha- and ER beta-mediated transcription are stimulated by Cd. Melatonin is a specific inhibitor of Cd-induced ER alpha-mediated transcription in both estrogen response elements (ERE)- and AP1-containing promoters, whereas ER beta-mediated transcription is not inhibited by the pineal indole. Moreover, the mutant ER alpha-(K302G, K303G), unable to bind calmodulin, is activated by Cd but becomes insensitive to melatonin treatment. These results proved that melatonin inhibits MCF7 cell growth induced by Cd and abolishes the stimulatory effect of the heavy metal in cells expressing ER alpha at both ERE-luc and AP1-luc sites. We can infer from these experiments that melatonin regulates Cd-induced transcription in both ERE- and AP1 pathways. These results also reinforce the hypothesis of the anti-estrogenic properties of melatonin as a valuable tool in breast cancer therapies.
镉（Cd）是一种重金属，可通过环境暴露和职业暴露影响人类健康。有证据表明，镉会在多个器官中蓄积，对人类具有致癌性。在体内，镉会模拟雌激素在子宫和乳腺中的作用。在雌激素反应性乳腺癌细胞系中，镉会刺激细胞增殖，并且还能独立于雌二醇激活雌激素受体。这种金属雌激素在MCF7细胞中增加基因表达的能力会被抗雌激素阻断，这表明这些化合物的活性是由雌激素受体α介导的。这项工作的目的是测试褪黑素是否能抑制镉诱导的MCF7细胞增殖，同时研究褪黑素是否能特异性抑制镉诱导的雌激素受体α反式激活。我们发现褪黑素可阻止镉诱导的同步化MCF7乳腺癌细胞生长。在瞬时转染实验中，我们证明雌激素受体α和雌激素受体β介导的转录均受到镉的刺激。褪黑素是镉诱导的雌激素受体α介导的转录在含雌激素反应元件（ERE）和含AP1的启动子中的特异性抑制剂，而松果体吲哚不会抑制雌激素受体β介导的转录。此外，无法结合钙调蛋白的突变型雌激素受体α（K302G、K303G）会被镉激活，但对褪黑素处理变得不敏感。这些结果证明，褪黑素可抑制镉诱导的MCF7细胞生长，并消除重金属在ERE - 荧光素酶和AP1 - 荧光素酶位点表达雌激素受体α的细胞中的刺激作用。我们可以从这些实验中推断，褪黑素在ERE和AP1途径中均调节镉诱导的转录。这些结果也强化了褪黑素具有抗雌激素特性这一假说，使其成为乳腺癌治疗中的一种有价值的工具。
