FEEDBACK REGULATION OF POLYAMINE SYNTHESIS AND TRANSPORT

多胺，亚精胺和精胺，以及它们的二胺前体， 腐胺存在于所有哺乳动物细胞中，是细胞生长所必需的 增长和活力。 哺乳动物细胞通过以下途径获得必需的多胺： 生物合成，或如果可用的话，通过从其环境中摄取。 在 在正常细胞中，多胺的细胞内水平被仔细地 管理，而癌细胞和病毒转化细胞经常 表现出这些化合物的异常升高 因为如此 相关性，有强烈的当前利益的发展， 用作抗肿瘤剂的多胺合成抑制剂，甚至 抗癌剂。 癌细胞也被注意到 外源性多胺比正常细胞更容易。 调查人员正在 试图利用这一属性来促进选择性的 潜在细胞毒性多胺类似物掺入肿瘤 细胞 到目前为止，这两种方法都证明有些令人失望， 很大程度上是因为我们不了解正常的控制机制 被细胞用来维持多胺水平。 由于这些原因， 该项目的长期目标是阐明，并可能 控制，哺乳动物细胞调节细胞的复杂机制。 细胞内的多胺水平是正常生理所必需的。 生物化学和分子技术，以及一些仓鼠和大鼠 细胞系，将用于研究三个不同方面的 多胺维持：a）关键生物合成酶的合成， 鸟氨酸脱羧酶; B）该酶的周转;和c）活性 多胺运输 所有这三个过程都受到 多胺水平的改变。 最近，一种变异的大鼠细胞系被 发现同时缺乏所有这些 多胺反馈反应。 这一观察表明， 这三种药物都有一种基本的亚精胺敏感反应 不同的细胞过程，这种共享的中间体或反应是 在变异细胞系中缺乏。 在调查中， 变异细胞中缺乏多胺反馈机制 将确定线路，从而在 反馈控制的鸟氨酸脱羧酶的稳定性，其中的东西 是已知的，那些鸟氨酸脱羧酶合成和多胺 运输，对此知之甚少。 这三个考试 维持细胞多胺水平的不同控制点 将产生一个多胺稳态的全面了解， 正常和癌症哺乳动物细胞，并将指导未来的努力， 通过操纵细胞多胺来改变异常生长。

The polyamines, spermidine and spermine, and their diamine precursor, putrescine, are found in all mammalian cells and are essential for cell growth and viability. Mammalian cells obtain the requisite polyamines by biosynthesis or, if available, by uptake from their environment. In normal cells, intracellular levels of the polyamines are carefully managed, whereas cancer cells and virally transformed cells frequently exhibit abnormal elevations of these compounds. Because of this correlation, there is intense current interest in the development of inhibitors of polyamine synthesis for use as anti-neoplastic, and even anti-carcinogenic, agents. Cancer cells also are noted to incorporate exogenous polyamines more readily than normal cells. Investigators are attempting to exploit this attribute to facilitate the selective incorporation of potentially cytotoxic polyamine analogs into tumor cells. Both these approaches have proven somewhat disappointing so far, in large part because we do not understand the normal control mechanisms utilized by a cell in maintaining polyamine levels. For these reasons, the long-term goal of this project is to elucidate, and potentially to control, the complex of mechanisms whereby mammalian cells regulate the intracellular polyamines levels that are essential for normal physiology. Biochemical and molecular techniques, as well as several hamster and rat cell lines, will be used to investigate three different aspects of polyamine maintenance: a) synthesis of the critical biosynthetic enzyme, ornithine decarboxylase; b) turnover of this enzyme; and c) active polyamine transport. All three processes are sensitively regulated by alterations in polyamine levels. Recently, a variant rat cell line was discovered that is simultaneously deficient in all of these polyamine-feedback responses. This observation suggests that some aspect of an essential spermidine-sensitive reaction is common to these three different cell processes, and this shared intermediate or reaction is deficient in the variant cell line. In the proposed investigation, the mechanism of polyamine feedback that is deficient in the variant cell line will be determined, thereby establishing a common link between the feedback control of ornithine decarboxylase stability, of which something is known, and those of ornithine decarboxylase synthesis and polyamine transport, about which very little is known. This examination of three different control points in the maintenance of cellular polyamine levels will yield a comprehensive understanding of polyamine homeostasis in normal and cancerous mammalian cells, and will guide future efforts to alter abnormal growth by manipulating cellular polyamines.