Metallothionein Isoform 3 and Renal Cadmium Toxicity

描述(申请人提供)：金属硫蛋白基因家族(MT-3)的亚型3于1992年首次被发现和分离，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MT家族的10个成员中是独一无二的，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，因为有证据表明，相当数量的MT-3mRNA和蛋白在人类肾脏的近端小管和其他上皮细胞中表达。在随后使用近端小管来源的细胞培养的研究中，申请人已经证明MT-3的基础表达参与维持近端小管的载体主动运输。其他研究表明，MT-3的基础表达参与了近端小管暴露于环境污染物镉所致的毒性。特异性目标1有三个目标，旨在确定MT-3在近曲小管向量主动转运中的作用。第一个目的是证明MT-3在近端小管细胞之间紧密连接的建立中起作用的假设，以及连接的紧密程度受MT-3基因表达水平的调节。第二个目标是证明MT-3独特的N-末端区域而不是C-末端区域是负责载体主动运输重建的表位的假设。最后一个目标是验证MT-3过度表达导致apoMT水平升高的假设。特异性目标2有三个目标，旨在确定MT-3在Cd+2诱导的肾毒性中的作用。一是验证近曲小管细胞中MT-3的基础水平通过一种成分参与紧密连接的形成和第二种成分与CD+2的结合和隔离而参与Cd+2抵抗的假说。第二种是验证MT-3基础表达参与细胞抵抗Cd+2诱导的细胞死亡的假说。第三个是验证MT-3的表达和对Cd+2的暴露改变了需要锌的转录因子的表达的假设。这项拟议研究的长期目标是确定近端小管MT-3表达在正常内稳态条件下和暴露于镉时的功能和调节作用。

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.