LIPOCORTINS (ANNEXINS) AND METAL-INDUCED MUTAGENESIS

描述：（改编自申请人的摘要）：重金属，如 Cr 2+、Ni 2+、Pb 2+、Cd 2+是环境毒物，被认为是 致癌物质。积累的证据表明，这些金属，在低 浓度，刺激培养细胞的DNA复制，而它们 同时抑制由另一种试剂引起的DNA损伤的修复过程。 因此，各种基因如癌基因和抑制基因的突变， 可能会形成，从而导致癌症。然而， 重金属的致突变作用仍然知之甚少。这种突变大多数 可能是由于复制机制的修改， 促进容易出错的DNA合成，绕过受损的碱基， 未鉴定的蛋白质，在重金属存在下，（a）结合 损伤的DNA，（B）解开损伤的DNA和/或（c）刺激易错DNA 用于跨损伤DNA合成的聚合酶。PT的实验室最近 发现纯化的脂皮质素I异源四聚体，一种核蛋白， 能够结合各种重金属，与 复制蛋白A（RP-A），单链DNA结合蛋白（SSB） 对DNA代谢的多个方面至关重要，包括修复， 重组和复制。我们假设脂皮质素I（和相关的 II）异源四聚体通过替换RP-A改变复制机制， 重金属的影响。使用纯化的脂皮质素异源四聚体和 具有化学修饰的易错DNA聚合酶（Pol）a、B或TI 多核苷酸作为受损的DNA模板，我们将执行以下操作 具体目的：（1）研究脂皮质素与受损DNA的结合， 重金属的存在，（2）检查受损DNA的解旋， 脂皮质素在重金属的存在下，和（3）研究刺激 存在下脂皮质素对跨损伤DNA合成的Pol a、B和n 重金属我们提出的研究将提供进一步的见解， 了解致癌的分子机制，遗传 不稳定和病理性疾病与形成 重金属引起的突变

DESCRIPTION: (Adapted from the Applicant's Abstract): Heavy metals such as Cr2+, Ni2+ Pb2+ and Cd2+ are environmental toxicants, and are regarded as carcinogens. Accumulated evidences have suggested that these metals, at low concentrations, stimulate DNA replication of cultured cells, while they simultaneously inhibit repair processes of DNA damage caused by another agent. Consequently, mutations of various genes such as oncogenes and suppressor genes could be formed, thereby causing cancer. However, the molecular mechanism of mutagenesis by heavy metals remains poorly understood. Such mutations are most likely to be resulted from modification of the replication machinery to facilitate error-prone DNA synthesis bypassing the damaged bases by an unidentified protein(s) that, in the presence of heavy metals, (a) binds to damaged DNA, (b) unwinds damaged DNA and/or (c) stimulates error-prone DNA polymerases for translesion DNA synthesis. The PT's laboratory has recently discovered that purified lipocortin I heterotetramer, a nuclear protein which is capable of binding various heavy metals, shares some common features with replication protein A (RP-A), a single strand DNA binding protein (SSB) essential for multiple aspects of DNA metabolism including repair, recombination and replication. We hypothesized that lipocortin I (and related II) heterotetramer alters the replicative machinery by replacing RP-A under the influence of heavy metals. Employing purified lipocortin heterotetramers and error-prone DNA polymerase (Pol) a, B or TI with chemically modified polynucleotides as damaged DNA templates, we will perform the following specific aims: (1) to investigate binding of lipocortins to damaged DNA in the presence of heavy metals, (2) to examine unwinding of damaged DNA by lipocortins in the presence of heavy metals, and (3) to study stimulation of Pol a, B and n by lipocortins for translesion DNA synthesis in the presence of heavy metals. Our proposed research will provide further insights to understanding of the molecular mechanisms of carcinogenesis, genetic instability and pathological diseases associated with the formation of mutations by heavy metals.