Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA.
J Biol Chem. 2012 Mar 2;287(10):7051-62. doi: 10.1074/jbc.M111.333120. Epub 2012 Jan 10.
The de novo thymidylate biosynthetic pathway in mammalian cells translocates to the nucleus for DNA replication and repair and consists of the enzymes serine hydroxymethyltransferase 1 and 2α (SHMT1 and SHMT2α), thymidylate synthase, and dihydrofolate reductase. In this study, we demonstrate that this pathway forms a multienzyme complex that is associated with the nuclear lamina. SHMT1 or SHMT2α is required for co-localization of dihydrofolate reductase, SHMT, and thymidylate synthase to the nuclear lamina, indicating that SHMT serves as scaffold protein that is essential for complex formation. The metabolic complex is enriched at sites of DNA replication initiation and associated with proliferating cell nuclear antigen and other components of the DNA replication machinery. These data provide a mechanism for previous studies demonstrating that SHMT expression is rate-limiting for de novo thymidylate synthesis and indicate that de novo thymidylate biosynthesis occurs at replication forks.
哺乳动物细胞中的从头胸苷酸生物合成途径为了进行 DNA 复制和修复而转移到细胞核中，该途径由丝氨酸羟甲基转移酶 1 和 2α（SHMT1 和 SHMT2α）、胸苷酸合成酶和二氢叶酸还原酶组成。在这项研究中，我们证明该途径形成了一个与核层粘连蛋白相关的多酶复合物。SHMT1 或 SHMT2α 对于二氢叶酸还原酶、SHMT 和胸苷酸合成酶共定位到核层粘连蛋白是必需的，表明 SHMT 作为支架蛋白对于复合物的形成是必不可少的。代谢复合物在 DNA 复制起始位点富集，并与增殖细胞核抗原和其他 DNA 复制机制的成分相关。这些数据为先前的研究提供了一种机制，表明 SHMT 表达是从头胸苷酸合成的限速步骤，并表明从头胸苷酸生物合成发生在复制叉上。
