Yu Ping, Li Zhengsheng, Zhang Ling, Tagle Danilo A, Cai Tao
Protein-nucleic acid interactions section, Structure Biophysics Laboratory, NCI-Frederick, Frederick, MD 21702, USA.
Gene. 2006 Jan 3;365:111-8. doi: 10.1016/j.gene.2005.09.034. Epub 2006 Jan 10.
Kynurenine aminotransferase (KAT) is an enzyme responsible for synthesis of kynurenic acid (KYNA), a well established neuroprotective and anticonvulsant agent, involved in synaptic transmission and implicated in the pathophysiology of schizophrenia, Huntington's disease and other neurological disorders. We have shown previously that kat2-/- mice had lower hippocampal KYNA levels and were more hyperactive than wild-type mice. However, these abnormalities occur early and are transitory coinciding with restoration of KYNA levels, suggesting that compensatory changes or ontogenetic expression of another unknown homolog may account for the normalization of KYNA levels in the adult kat2-/- mice brain. Here, we report the isolation of a novel KAT molecule, kat3, from mouse and human brain cDNA libraries. The encoded 454 amino acids of human KAT III share 64.8% similarity to that of KAT I and 30.1% to KAT II. Northern blot analysis demonstrated that kat3 mRNA is widely expressed but with higher expression levels in liver, kidney, heart, and neuroendocrine tissues. RT-PCR and Northern analysis showed that kat3 expression starts as early as postnatal day (PND) 7 and peaks in adult. The mRNA level of kat3 and kat1 when measured together is significantly higher at PND 60 in kat2-/- mice than those of wild-type mice indicating possible co-regulation of expression levels. RNA-interference (RNAi) directed towards transcripts for either R03A10.4 or F28H6.3 in Caenorhabditis elegans which are kat1 and kat3 orthologs, respectively, did not result in any gross abnormalities. Our results show that upregulation of kat3 and kat1 may be responsible for the phenotypic rescue on kat2-/- mice.
犬尿氨酸转氨酶（KAT）是一种负责合成犬尿喹啉酸（KYNA）的酶，犬尿喹啉酸是一种公认的具有神经保护作用和抗惊厥作用的物质，参与突触传递，并与精神分裂症、亨廷顿舞蹈症及其他神经疾病的病理生理学有关。我们之前已经表明，kat2基因敲除小鼠的海马体中KYNA水平较低，且比野生型小鼠更加多动。然而，这些异常情况出现得较早且是暂时的，与KYNA水平的恢复同时发生，这表明代偿性变化或另一种未知同源物的个体发生表达可能是成年kat2基因敲除小鼠大脑中KYNA水平正常化的原因。在此，我们报告了从小鼠和人类大脑cDNA文库中分离出一种新型KAT分子——kat3。人类KAT III编码的454个氨基酸与KAT I的相似性为64.8%，与KAT II的相似性为30.1%。Northern印迹分析表明，kat3 mRNA广泛表达，但在肝脏、肾脏、心脏和神经内分泌组织中表达水平较高。RT-PCR和Northern分析表明，kat3的表达最早在出生后第7天开始，并在成年时达到峰值。在出生后第60天，同时测量kat3和kat1的mRNA水平时，kat2基因敲除小鼠中的水平显著高于野生型小鼠，表明表达水平可能存在共同调节。分别针对秀丽隐杆线虫中kat1和kat3的直系同源物R03A10.4或F28H6.3的转录本进行RNA干扰（RNAi），并未导致任何明显异常。我们的结果表明，kat3和kat1的上调可能是kat2基因敲除小鼠表型拯救的原因。
