FEEDBACK REGULATION OF POLYAMINE SYNTHESIS AND TRANSPORT

所述多胺、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，是细胞所必需的 成长和生存能力。哺乳动物细胞通过以下途径获得必需的多胺 生物合成，或者，如果可能，通过从他们的环境中吸收。在……里面 正常细胞中，细胞内多胺的水平是小心的 管理，而癌细胞和病毒转化的细胞经常 显示出这些化合物的异常海拔。正因为如此 与此相关的是，目前人们对发展 多胺合成的抑制剂，用于抗肿瘤，甚至 抗癌、抗癌剂。癌细胞也被认为包含了 外源性多胺比正常细胞更容易产生。调查人员正在 试图利用这一属性来促进选择性的 潜在的细胞毒性多胺类似物在肿瘤中的掺入 细胞。到目前为止，这两种方法都被证明有些令人失望， 很大程度上是因为我们不了解正常的控制机制 细胞用来维持多胺水平。出于这些原因， 这个项目的长期目标是阐明，并可能 控制，哺乳动物细胞调节的复杂机制 细胞内多胺水平是正常生理所必需的。 生化和分子技术，以及几种仓鼠和大鼠 细胞系，将被用来研究三个不同方面的 多胺维持：a)合成关键的生物合成酶， 鸟氨酸脱羧酶；b)该酶的周转；c)活性 多胺运输。所有这三个过程都受到 多胺水平的变化。最近，一种变异的大鼠细胞系 发现同时在所有这些方面都有缺陷 多胺-反馈反应。这一观察结果表明，在某些方面 一种基本的亚精胺敏感反应是这三种反应的共同点 不同的细胞过程，这种共享的中间体或反应是 缺乏变异的细胞系。在拟议的调查中， 变异细胞中缺失的多胺反馈机制 线路将被确定，从而在 鸟氨酸脱羧酶稳定性的反馈控制 已知，以及鸟氨酸脱羧酶的合成和多胺的合成 交通运输，人们对此知之甚少。这次考试有三个 维持细胞多胺水平的不同控制点 将产生对多胺动态平衡的全面理解 正常和癌变的哺乳动物细胞，并将指导未来的努力 通过操纵细胞型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.