Curiel D T, Holmes M D, Okayama H, Brantly M L, Vogelmeier C, Travis W D, Stier L E, Perks W H, Crystal R G
Pulmonary Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland.
J Biol Chem. 1989 Aug 15;264(23):13938-45.
Alpha 1-Antitrypsin (alpha 1AT) deficiency is characterized by reduced serum levels of alpha 1AT and a risk for the development of emphysema and liver disease. However, whereas there is an increased risk for emphysema associated with at least 10 alpha 1AT deficiency and null alleles, the hepatic disease is observed only in a subset of these alleles, suggesting that it is not the reduced serum levels of alpha 1AT per se which cause the liver disease. The present study characterizes the alpha 1AT deficiency allele Mmalton, an allele that like the common Z deficiency mutation (Glu342----Lys) is associated with both alpha 1AT deficiency and hepatic disease. Capitalizing on the identification of the homozygous inheritance of the rare Mmalton alpha 1AT deficiency allele, it was demonstrated that although caused by a very different mutation, the Mmalton allele shares with the Z allele the association of liver disease with the same type of abnormalities of alpha 1AT biosynthesis. Cloning of the Mmalton gene and sequence analysis demonstrated that it differs from the normal alpha 1AT M2 allele by deletion of the entire codon (TTC) for residue Phe52. Liver biopsy of the Mmalton homozygote revealed inflammation, mild fibrosis, and intrahepatocyte accumulation of alpha 1AT. Evaluation of de novo alpha 1AT biosynthesis in alpha 1AT-synthesizing cells of this individual demonstrated normal levels of alpha 1AT mRNA transcripts but abnormal intracellular accumulation of newly synthesized alpha 1AT at the level of the rough endoplasmic reticulum with consequent reduced alpha 1AT secretion. Finally, retroviral gene transfer of a normal alpha 1AT cDNA and an alpha 1AT cDNA with the Mmalton Phe52 deletion into murine cells demonstrated that the Mmalton cells reproduced the abnormal accumulation of newly synthesized alpha 1AT, thus directly demonstrating that the deletion mutation is responsible for the intracellular accumulation of the newly synthesized alpha 1AT. Thus, not only is the liver disease associated with alpha 1AT deficiency restricted to a subset of alpha 1AT deficiency alleles, it appears to be restricted to those alleles associated with intracellular accumulation of newly synthesized alpha 1AT, suggesting that it is the abnormal intrahepatocyte alpha 1AT accumulation which incites the liver injury.
α1 -抗胰蛋白酶（α1AT）缺乏症的特征是血清α1AT水平降低，以及患肺气肿和肝病的风险增加。然而，虽然与至少10种α1AT缺乏症和无效等位基因相关的肺气肿风险增加，但肝病仅在这些等位基因的一个子集中观察到，这表明并非血清α1AT水平本身降低导致了肝病。本研究对α1AT缺乏症等位基因Mmalton进行了特征描述，该等位基因与常见的Z缺乏突变（Glu342→Lys）一样，与α1AT缺乏症和肝病都有关联。利用对罕见的Mmaltonα1AT缺乏症等位基因纯合遗传的鉴定，证明尽管由非常不同的突变引起，但Mmalton等位基因与Z等位基因一样，肝病与α1AT生物合成的相同类型异常相关。Mmalton基因的克隆和序列分析表明，它与正常的α1AT M2等位基因不同，缺失了编码苯丙氨酸（Phe）52残基的整个密码子（TTC）。Mmalton纯合子的肝活检显示有炎症、轻度纤维化以及α1AT在肝细胞内积聚。对该个体α1AT合成细胞中从头合成α1AT的评估表明，α1AT mRNA转录本水平正常，但新合成的α1AT在粗面内质网水平出现异常的细胞内积聚，从而导致α1AT分泌减少。最后，将正常的α1AT cDNA和带有Mmalton苯丙氨酸52缺失的α1AT cDNA通过逆转录病毒基因转移到小鼠细胞中，结果表明Mmalton细胞再现了新合成的α1AT的异常积聚，从而直接证明缺失突变是新合成的α1AT细胞内积聚的原因。因此，不仅与α1AT缺乏症相关的肝病局限于α1AT缺乏症等位基因的一个子集，似乎还局限于那些与新合成的α1AT细胞内积聚相关的等位基因，这表明是肝细胞内α1AT的异常积聚引发了肝损伤。
