Metallothionein Isoform 3 and Renal Cadmium Toxicity

描述（由申请人提供）：金属硫蛋白基因家族（MT-3）的同种型3于1992年首次被识别和分离，并被指定为脑特异性家族成员。对神经系统的详细研究表明，MT-3在10个MT家族成员中是独特的，因为它除了具有金属结合能力外，还具有生长抑制活性。申请人是第一个证明MT-3在神经系统外表达的人，当时显示相当数量的MT-3 mRNA和蛋白质在人肾的近端小管和其他上皮细胞中表达。在使用近端小管衍生的细胞培养物的后续研究中，申请人已经表明MT-3的基础表达参与近端小管载体主动转运的维持。其他研究表明，MT-3的基础表达参与介导近端小管暴露于环境污染物镉导致的毒性。具体目标1有三个目标，旨在确定MT-3在近端小管载体主动转运中的作用。第一个目的是证明MT-3在近曲小管细胞之间紧密连接的建立中起作用，并且连接的“紧密性”程度受MT-3基因表达水平调节的假设。第二个目的是证明MT-3的独特的N-末端区域，而不是C-末端区域，是负责重建载体主动转运的表位。最后一个目标是检验MT-3过表达导致apoMT水平升高的假设。具体目标2有三个目标，旨在确定MT-3表达在Cd+2诱导的肾毒性中的作用。第一个是测试的假设，MT-3的基础水平在近端小管细胞有助于通过一个组件分配到紧密连接的形成和第二个组件分配到镉+2的结合和螯合的Cd +2电阻。第二是检验MT-3的基础表达参与细胞对Cd+2诱导的凋亡性细胞死亡的抵抗的假设。第三个是测试的假设，MT-3的表达和暴露于Cd+2改变的Zn+2需要的转录因子的表达。该研究的长期目标是确定MT-3在正常稳态条件下和暴露于镉时近端小管中表达的功能和调节作用。

DESCRIPTION (provided by applicant): Isoform 3 of the metallothionein gene family (MT-3) was first recognized and isolated in 1992 and designated as a brain-specific family member. Detailed studies in the neural system demonstrated that MT-3 was unique among the 10 MT family members in that it possessed, in addition to a metal binding capability, a growth inhibitory activity. The applicant was the first to demonstrate that MT-3 was expressed outside the neural system when it was shown that appreciable amounts of MT-3 mRNA and protein were expressed in the proximal tubule and other epithelial cells of the human kidney. In subsequent studies using proximal tubule-derived cell cultures, the applicant has shown that the basal expression of MT-3 is involved in the maintenance of proximal tubule vectorial active transport. Other studies have shown that basal expression of MT-3 participates in mediating the toxicity resulting from exposure of the proximal tubule to the environmental pollutant, cadmium. Specific aim 1 has three goals designed to define the role of MT-3 in proximal tubule vectorial active transport. The first is to prove the hypothesis that MT-3 functions in the establishment of about tight junctions between proximal tubule cells and that the degree of "tightness" of the junctions is regulated by the level of MT-3 gene expression The second goal is to prove the hypothesis that the unique N-terminal region of MT-3, and not the C-terminal region, is the epitope responsible for the re-establishment of vectorial active transport. The last goal is to test the hypothesis that the overexpression of MT-3 results in elevated levels of apoMT. Specific aim 2 has three goals designed to define the role of MT-3 expression in Cd+2-induced nephrotoxicity. The first is to test the hypothesis that the basal level of MT-3 in the proximal tubule cell contributes to Cd+2 resistance through one component assignable to tight junction formation and a second component assignable to the binding and sequestration of Cd+2. The second is to test the hypothesis that the basal expression of MT-3 participates in the cell's resistance to Cd+2-induced apoptotic cell death. The third is to test the hypothesis that MT-3 expression and exposure to Cd+2 alters the expression of Zn+2-requiring transcription factors. The long term goal of the proposed research is to define the functional and regulatory role of MT-3 expression in the proximal tubule under conditions of normal homeostasis and when exposed to cadmium.