Molecular basis of Japanese variants of pyrimidine 5′-nucleotidase deficiency
Molecular basis of Japanese variants of pyrimidine 5′-nucleotidase deficiency
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DOI：
10.1111/j.1365-2141.2004.05029.x
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发表时间：
2004-07-01
影响因子：
6.5
通讯作者：
Fujii, H
中科院分区：
文献类型：
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作者：
Kanno, H;Takizawa, T;Fujii, H
嘧啶5 '-核苷酸酶（P5 N-I）的I型亚型在红系成熟过程中嘧啶单核苷酸的催化中具有重要作用。已经鉴定了两种P5 N-I mRNA的选择性剪接形式，我们在网织红细胞中发现了另一种选择性剪接形式，其中包括额外的87-bp序列。该序列位于外显子2的下游6.2 kb和外显子3序列的上游2.7 kb;因此，P5 N-I基因编码11个外显子，其跨度约为48 kb。我们在9个P5 N-I缺陷症家系中发现了5个新的突变：2个错义突变（425 C，721 C），1个剪接突变（339 C），1个1-bp插入（251-insA-252）和1个9-bp缺失（del 192-200）。所有患者均为每种突变的纯合子。具有721 C（G241 R）的突变体P5 N-I对胞苷一磷酸具有较低的亲和力，表明Gly 241对底物结合是重要的。单倍型分析表明，721 C，已确定在5个无关的家庭，是一个创始人突变。然后在Cos-7中表达突变体P5 N。P5 N与425 C（L142 P）的降解明显快于野生型对照，蛋白酶体抑制剂恢复L142 P的稳定性。这些数据表明，L142 P增加了对泛素-蛋白酶体途径降解的敏感性。
The type-I isoform of pyrimidine 5'-nucleotidase (P5N-I) has an important role in the catabolism of pyrimidine mononucleotides during erythroid maturation. Two alternatively spliced forms of P5N-I mRNA have been identified, and we found another alternatively spliced form in reticulocytes, which included an additional 87-bp sequence. The sequence is located 6.2-kb downstream of the exon 2 and 2.7-kb upstream of the exon 3 sequence; consequently, the P5N-I gene encodes 11 exons, which span approximately 48 kb. We identified five novel mutations in nine families with P5N-I deficiency: two missense mutations (425C, 721C), one splice mutation (339C), one 1-bp insertion (251-insA-252) and one 9-bp deletion (del 192-200). All patients were homozygous for each mutation. The mutant P5N-I with 721C (G241R) had lower affinity for cytidine monophosphate, suggesting that Gly241 is important for substrate binding. Haplotype analysis showed that 721C, which had been identified in five unrelated families, was a founder mutation. The mutant P5N was then expressed in Cos-7. The degradation of P5N with 425C (L142P) was significantly faster than a wild-type control, and proteasome inhibitors restored the stability of L142P. These data suggest that L142P increases susceptibility to the degradation by the ubiquitin-proteasome pathway.