SHMT1 and SHMT2 are functionally redundant in nuclear de novo thymidylate biosynthesis.
SHMT1 and SHMT2 are functionally redundant in nuclear de novo thymidylate biosynthesis.
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DOI：
10.1371/journal.pone.0005839
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发表时间：
2009-06-09
期刊：
影响因子：
3.7
通讯作者：
Stover PJ
中科院分区：
文献类型：
--
作者：
Anderson DD;Stover PJ
在哺乳动物中构成从头胸苷酸合成途径的三种酶，细胞质丝氨酸羟甲基转移酶（SHMT 1）、胸苷酸合成酶（TYMS）和二氢叶酸还原酶（DHFR）在S期期间经历类小泛素化和核输入。在这项研究中，我们证明了纯化的完整小鼠肝细胞核在NADPH和丝氨酸的存在下将dUMP转化为dTMP。无论是核提取物，也不完整的细胞核暴露于氨甲基膦酸盐，SHMT抑制剂，表现出胸苷酸合成活性。从Shmt 1 −/−小鼠肝脏分离的细胞核保留了从野生型小鼠分离的细胞核所表现出的25%的胸苷酸合成活性。这种残余活性是由于存在由Shmt 2编码的SHMT的胞质/核同工酶。Shmt 2被证明编码两种转录本，一种编码专门定位于线粒体的蛋白质（SHMT 2），另一种转录本缺乏外显子1，编码在S期定位于细胞质和细胞核的蛋白质（SHMT 2 α）。Shmt 2编码SHMT胞质同工酶的能力可能解释了Shmt 1 −/−小鼠的生存能力，并提供了允许人类SHMT 1 L474 F多态性扩展的冗余，该多态性损害了SHMT 1类小泛素化和核转位。
The three enzymes that constitute the de novo thymidylate synthesis pathway in mammals, cytoplasmic serine hydroxymethyltransferase (SHMT1), thymidylate synthase (TYMS) and dihydrofolate reductase (DHFR) undergo sumoylation and nuclear import during S-phase. In this study, we demonstrate that purified intact mouse liver nuclei convert dUMP to dTMP in the presence of NADPH and serine. Neither nuclear extracts nor intact nuclei exposed to aminomethylphosphonate, a SHMT inhibitor, exhibit thymidylate synthesis activity. Nuclei isolated from Shmt1−/− mouse livers retained 25% of thymidylate synthesis activity exhibited by nuclei isolated from wild type mice. This residual activity was due to the presence of a cytoplasmic/nuclear isozyme of SHMT encoded by Shmt2. Shmt2 is shown to encode two transcripts, one which encodes a protein that localizes exclusively to the mitochondria (SHMT2), and a second transcript that lacks exon 1 and encodes a protein that localizes to the cytoplasm and nucleus during S-phase (SHMT2α). The ability of Shmt2 to encode a cytoplasmic isozyme of SHMT may account for the viability of Shmt1−/− mice and provide redundancy that permitted the expansion of the human SHMT1 L474F polymorphism that impairs SHMT1 sumoylation and nuclear translocation.