Chromium(VI) down-regulates heavy metal-induced metallothionein gene transcription by modifying transactivation potential of the key transcription factor, metal-responsive transcription factor 1
Chromium(VI) down-regulates heavy metal-induced metallothionein gene transcription by modifying transactivation potential of the key transcription factor, metal-responsive transcription factor 1
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DOI：
10.1074/jbc.m302887200
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发表时间：
2003-07-11
影响因子：
4.8
通讯作者：
Jacob, ST
中科院分区：
文献类型：
--
作者：
Majumder, S;Ghoshal, K;Jacob, ST
重金属如锌和镉对金属硫蛋白-I和金属硫蛋白-II(MT-I和MT-II)基因的强烈诱导需要特定的转录因子金属反应转录因子1(MTF1)。铬(VI)是一种主要的环境致癌物，它不仅不能激活这些基因，而且还能抑制锌或镉对这些基因的诱导。重金属诱导的另一个MTF1靶基因锌转运蛋白1(ZNT-1)的表达也被Cr6+下调。相比之下，两个不依赖MTF1的CD2+诱导基因--血红素加氧酶1(HO-1)和HSP-70对Cr6+不敏感。Cr6+也不影响看家基因的表达，如GAPDH或β-肌动蛋白。MT基因的关键反式激活因子MTF1高表达的稳定细胞株对Cr6+的抑制作用表现出不同程度的抗性，表明MTF1是铬毒害的靶标。细胞经Cr6+处理后，MTF1与金属反应元件的基础结合和诱导结合不受影响。瞬时转染研究表明，Cr6+显著降低了MTF1反式激活MT-I启动子的能力。由Gal-4DNA结合区和MTF1的一个或多个反式激活结构域组成的融合蛋白，即酸性结构域、富含脯氨酸结构域和富含丝氨酸-苏氨酸结构域，对Gal-4驱动的荧光素酶基因有不同程度的激活作用，但都对Cr6+敏感。未表达MTF1的细胞在加入含Cr6+的锌或镉后易发生凋亡，而高表达MTF1的细胞则明显延迟了开始凋亡的时间。
The robust induction of metallothionein-I and II (MT-I and MT-II) genes by several heavy metals such as zinc and cadmium requires the specific transcription factor metal-responsive transcription factor 1 (MTF1). Chromium (VI), a major environmental carcinogen, not only failed to activate these genes but also inhibited their induction by Zn2+ or Cd2+. The heavy metal-induced expression of another MTF1 target gene, zinc transporter 1 (ZnT-1), was also down-regulated by Cr6+. By contrast, the expression of two MTF1-independent Cd2+-inducible genes, heme oxygenase 1 (HO-1) and HSP-70, was not sensitive to Cr6+. Cr6+ did not also affect the expression of housekeeping genes such as GAPDH or beta-actin. Stable cell lines overexpressing variable levels of MTF1, the key transactivator of the MT genes, demonstrated differential resistance toward the inhibitory effect of Cr6+, indicating MTF1 as a target of chromium toxicity. The basal and inducible binding of MTF1 to metal response elements was not affected by treatment of cells with Cr6+. Transient transfection studies showed that the ability of MTF1 to transactivate the MT-I promoter was significantly compromised by Cr6+. The fusion protein consisting of a Gal-4 DNA binding domain and one or more of the three transactivation domains of MTF1, namely the acidic domain, proline-rich domain, and serine-threonine rich domain, activated the GAL-4-driven luciferase gene to different degrees, but all were sensitive to Cr6+. MTF1 null cells were prone to apoptosis after exposure to Zn2+ or Cd2+ that was augmented in presence Cr6+, whereas the onset of apoptosis was significantly delayed in cells overexpressing MTF1.