Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Mutat Res. 2010 Nov 28;703(1):43-50. doi: 10.1016/j.mrgentox.2010.06.009. Epub 2010 Jun 22.
Inosine triphosphate pyrophosphatase (ITPA protein) (EC 3.6.1.19) hydrolyzes deaminated purine nucleoside triphosphates, such as ITP and dITP, to their corresponding purine nucleoside monophosphate and pyrophosphate. In mammals, this enzyme is encoded by the Itpa gene. Using the Itpa gene-disrupted mouse as a model, we have elucidated the biological significance of the ITPA protein and its substrates, ITP and dITP. Itpa(-/-) mice exhibited peri- or post-natal lethality dependent on the genetic background. The heart of the Itpa(-/-) mouse was found to be structurally and functionally abnormal. Significantly higher levels of deoxyinosine and inosine were detected in nuclear DNA and RNA prepared from Itpa(-/-) embryos compared to wild type embryos. In addition, an accumulation of ITP was observed in the erythrocytes of Itpa(-/-) mice. We found that Itpa(-/-) primary mouse embryonic fibroblasts (MEFs), which have no detectable ability to generate IMP from ITP in whole cell extracts, exhibited a prolonged population-doubling time, increased chromosome abnormalities and accumulation of single-strand breaks in their nuclear DNA, in comparison to primary MEFs prepared from wild type embryos. These results revealed that (1) ITP and dITP are spontaneously produced in vivo and (2) accumulation of ITP and dITP is responsible for the harmful effects observed in the Itpa(-/-) mouse. In addition to its effect as the precursor nucleotide for RNA transcription, ITP has the potential to influence the activity of ATP/GTP-binding proteins. The biological significance of ITP and dITP in the nucleotide pool remains to be elucidated.
肌苷三磷酸磷酸酶（ITPA 蛋白）（EC 3.6.1.19）水解脱氨基嘌呤核苷三磷酸，如 ITP 和 dITP，生成相应的嘌呤核苷一磷酸和焦磷酸。在哺乳动物中，这种酶由 Itpa 基因编码。我们使用 Itpa 基因敲除小鼠作为模型，阐明了 ITPA 蛋白及其底物 ITP 和 dITP 的生物学意义。Itpa(-/-) 小鼠表现出围产期或出生后致死性，依赖于遗传背景。Itpa(-/-) 小鼠的心脏被发现结构和功能异常。与野生型胚胎相比，从 Itpa(-/-) 胚胎中提取的核 DNA 和 RNA 中检测到脱氧肌苷和肌苷的水平显著升高。此外，在 Itpa(-/-) 小鼠的红细胞中观察到 ITP 的积累。我们发现，Itpa(-/-) 原代小鼠胚胎成纤维细胞（MEFs）在全细胞提取物中没有检测到从 ITP 生成 IMP 的能力，与从野生型胚胎中制备的原代 MEFs 相比，其群体倍增时间延长，染色体异常增加，核 DNA 中单链断裂积累。这些结果表明：(1)ITP 和 dITP 在体内自发产生；(2)ITP 和 dITP 的积累是导致 Itpa(-/-) 小鼠观察到的有害影响的原因。除了作为 RNA 转录前体核苷酸的作用外，ITP 还有可能影响 ATP/GTP 结合蛋白的活性。核苷酸池中的 ITP 和 dITP 的生物学意义仍有待阐明。
