REGULATION OF CARBAMYL PHOSPH SYNTHETASES BY MAP KINASE

从头核苷酸合成的调节对于关键的细胞内构件如核酸聚合物DNA和RNA的组装是至关重要的。 最终，细胞增殖的速率由这些分子的合成速率决定;因此，这些途径已被靶向用于异常细胞生长的治疗控制（癌症化疗）。 然而，正常生长信号控制核苷酸合成的机制还不清楚。 与此相反，最近已经取得了相当大的进展，在确定的生长因子激活的信号通路，有助于细胞生长调节。 一种这样的途径被称为促分裂原活化蛋白激酶（MAP激酶）级联，并且由通过可逆磷酸化调节细胞信号传导的蛋白激酶组成。 MAPK途径被认为在确定细胞增殖速率中起核心作用，并且被多种生长促进信号激活。 虽然这一途径的基本组成部分是已知的，但这些调节的许多目标尚未阐明。我们最近发现了MAP激酶信号传导和尿苷核苷酸生物合成中的关键酶CAD控制之间存在联系的证据。 CAD由氨甲酰磷酸合成酶（CPS II）、天冬氨酸转氨甲酰酶和二氢乳清酸酶三种酶组成。 CAD催化细胞中尿苷核苷酸合成中的限速步骤，并且该酶的活性在具有增加的生长速率的细胞（即肿瘤细胞）中增加。 因此，本建议的直接目标是在生化水平上研究MAP激酶参与调节CAD活性以及这种调节对从头尿苷核苷酸生物合成的后果。 本研究的长期目标是更好地了解生长促进信号对核苷酸生物合成的调控。 最终，随着生长因子激活激酶信号通路的有效和选择性抑制剂的设计，可能实现用于调节核苷酸代谢和细胞生长的新策略。

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.