抗凝血酶基因T98I和A404T突变导致抗凝血酶缺陷症的分子机制研究

目的研究抗凝血酶（AT）基因T98I和A404T突变致AT缺陷症的分子机制。方法构建AT野生型和突变体表达质粒（ATwt、ATT98I、ATA404T）并瞬时转染至COS-7细胞或CHO细胞,进行体外表达试验、脉冲-追踪试验和细胞免疫荧光染色;用荧光实时PCR（RT—PCR）检测转染细胞ATmRNA表达量的改变;蛋白降解抑制实验检测突变蛋白在细胞内的降解途径。结果ATT98I未从转染细胞内分泌且在细胞内逐渐降解,ATA404T仅部分从细胞内分泌、大部分未分泌并在细胞内逐渐降解。RT—PCR显示,与野生型ATmRNA相比,突变体ATmRNA不降低。脉冲-追踪试验发现,这两种AT突变体分泌障碍,未在细胞内聚集而是降解。蛋白降解抑制实验显示,突变体ATT98I通过蛋白体酶途径进行细胞内降解。转染细胞荧光染色显示,转染ATT98I质粒的CHO细胞内荧光强度明显减弱、无明显核周聚集,而转染ATA404T质粒的CHO细胞内荧光减弱且弥散分布于胞质、核周有轻度聚集。结论分泌障碍和细胞内降解是AT基因T98I和A404T突变导致AT缺陷症的分子病理机制。

Molecular mechanisms of antithrombin deficiency caused by T98I and A404T mutation

OBJECTIVE: To study the molecular mechanisms of antithrombin (AT) deficiency caused by AT gene mutations T98I and A404T. METHODS: Wild-type and mutant AT cDNA expression plasmids (ATwt, AT T98I and AT A404T) were constructed and transfected into the monkey fibroblast of the line COS-7 or Chinese hamster ovary (CHO) cells. NH4Cl. ALLN and brefeldin A were added. ELISA was used to detect the AT: Ag. Pulse-chase experiment and immunofluorescence assay were used to detect the radioactivity of the 35S-labeled AT. Fluorescence real-time PCR was used to detect the expression of AT mRNA, protein degradation inhibition was used to elucidate the mutant T98I degradation pathway inside the cells. RESULTS: AT T98I was not secreted from the cells and was gradually degraded inside the cells. There was partial secretion of AT A404T, but most of the molecule was not secreted but was degraded intracellularly. Fluorescence real-time PCR indicated that the mutant AT mRNA was transcribed at a similar or even higher level as that of wild-type (wt). Pulse-chase labeling studies suggested both AT variants did not accumulate, but degraded intracellularly. Protein degradation inhibition experiment showed that mutant AT T98I was degraded intracellularly through the proteasome pathway. Immunohistochemical staining of the transfected cells revealed that CHO cells expressing the AT T98I mutant were stained diffusely without perinuclear enhancement and cells expressing AT A404T mutant mainly in the whole cytoplasm with weaker perinuclear enhancement. CONCLUSION: Impaired secretion of the mutant AT molecules, due to intracellular degradation, is the molecular mechanism of AT deficiency caused by T98I and A404T mutation.