REGULATION OF CARBAMYL PHOSPH SYNTHETASES BY MAP KINASE

从头合成核苷酸的调节对于关键的细胞内构建单元的组装至关重要，如核酸聚合物DNA和RNA。最终，细胞增殖的速度由这些分子的合成速度决定；因此，这些途径被作为治疗控制异常细胞生长的靶点(癌症化疗)。然而，正常生长信号控制核苷酸合成的机制还不是很清楚。相比之下，最近在识别有助于细胞生长调节的生长因子激活的信号通路方面取得了相当大的进展。其中一个途径被称为丝裂原激活的蛋白激酶(MAP)级联，由蛋白激酶组成，通过可逆的磷酸化来调节细胞信号。MAPK通路被认为在决定细胞增殖速度中起着核心作用，并被多种促生长信号激活。虽然这一途径的基本成分已知，但这些调控的许多靶点尚未阐明。我们最近发现了MAP激酶信号与尿苷核苷酸生物合成中一种关键酶(CAD)的控制之间存在联系的证据。CAD由三种酶组成：氨基甲酰磷酸合成酶(CPS II)、天冬氨酸转氨甲基酶和二氢丙酸酶。CAD催化细胞内尿苷核苷酸合成的限速步骤，在生长速度加快的细胞(即肿瘤细胞)中，该酶的活性增加。因此，这一建议的直接目标是在生化水平上研究MAP激酶参与调节CAD活性以及这一调节对尿苷核苷酸生物合成的影响。这项研究的长期目标是更好地了解促进生长信号对核苷酸生物合成的调控。最终，随着生长因子激活的激酶信号通路的有效和选择性抑制剂的设计，调节核苷酸代谢和细胞生长的新策略可能会实现。

The regulation of de novo nucleotide synthesis is critical to the assembly of key intracellular building blocks such as the nucleic acid polymers DNA and RNA. Ultimately the rate of cell proliferation is determined by the rate of synthesis of these molecules; consequently these pathways have been targeted for therapeutic control of aberrant cell growth (cancer chemotherapy). However, the mechanisms by which normal growth signals control nucleotide synthesis are not well understood. In contrast, considerable progress has recently been achieved in the identification of growth factor-activated signaling pathways that contribute to cellular growth regulation. One such pathway is known as the mitogen-activated protein kinase (MAP kinase) cascade and is composed of protein kinases that regulate cellular signaling by reversible phosphorylation. The MAPK pathway is believed to play a central role in the determination of the rate of cellular proliferation and is activated by a multitude of growth promoting signals. Although the basic components of this pathway are known, many of the targets these regulations have yet to be elucidated. We recently found evidence for a link between MAP kinase signaling and the control of a key enzyme in uridine nucleotide biosynthesis known as CAD. CAD is composed of three enzymes carbamyl phosphate synthetase (CPS II), aspartate transcarbamylase and dihydrooratase. CAD catalyzes the rate- limiting step in uridine nucleotide synthesis in cells and the activity of this enzyme is increased in cells with increased growth rates (i.e. tumor cells). Therefore, the immediate objective of this proposal is to investigate at a biochemical level the involvement of MAP kinase in regulating CAD activity and the consequences of this regulation on de novo uridine nucleotide biosynthesis. The long-term goal of this study is to gain a greater understanding of the regulation of nucleotide biosynthesis by growth promoting signals. Eventually with the design of potent and selective inhibitors of growth factor-activated kinase signaling pathways, novel strategies for the regulation of nucleotide metabolism and cell growth may be achieved.