Department of Metabolic and Endocrine Diseases, University Medical Center (UMC) Utrecht, The Netherlands.
Hepatology. 2010 Jan;51(1):286-96. doi: 10.1002/hep.23268.
Deficiency in P-type ATP8B1 is a severe and clinically highly variable hereditary disorder that is primarily characterized by intrahepatic cholestasis. It presents either as a progressive (progressive familial intrahepatic cholestasis type 1 [PFIC1]) or intermittent (benign recurrent intrahepatic cholestasis type 1 [BRIC1]) disease. ATP8B1 deficiency is caused by autosomal recessive mutations in the gene encoding ATP8B1, a putative aminophospholipid-translocating P-type adenosine triphosphatase. The exact pathogenesis of the disease is elusive, and no effective pharmacological therapy is currently available. Here, the molecular consequences of six distinct ATP8B1 missense mutations (p.L127P, p.G308V, p.D454G, p.D554N, p.I661T, and p.G1040R) and one nonsense mutation (p.R1164X) associated with PFIC1 and/or BRIC1 were systematically characterized. Except for the p.L127P mutation, all mutations resulted in markedly reduced ATP8B1 protein expression, whereas messenger RNA expression was unaffected. Five of seven mutations resulted in (partial) retention of ATP8B1 in the endoplasmic reticulum. Reduced protein expression was partially restored by culturing the cells at 30 degrees C and by treatment with proteasomal inhibitors, indicating protein misfolding and subsequent proteosomal degradation. Protein misfolding was corroborated by predicting the consequences of most mutations onto a homology model of ATP8B1. Treatment with 4-phenylbutyrate, a clinically approved pharmacological chaperone, partially restored defects in expression and localization of ATP8B1 substitutions G308V, D454G, D554N, and in particular I661T, which is the most frequently identified mutation in BRIC1.
A surprisingly large proportion of ATP8B1 mutations resulted in aberrant folding and decreased expression at the plasma membrane. These effects were partially restored by treatment with 4-phenylbutyrate. We propose that treatment with pharmacological chaperones may represent an effective therapeutic strategy to ameliorate the recurrent attacks of cholestasis in patients with intermittent (BRIC1) disease.
P 型 ATP8B1 的缺乏是一种严重且临床上高度可变的遗传性疾病，主要表现为肝内胆汁淤积。它表现为进行性（进行性家族性肝内胆汁淤积症 1 型 [PFIC1]）或间歇性（良性复发性肝内胆汁淤积症 1 型 [BRIC1]）疾病。ATP8B1 缺乏症是由编码 ATP8B1 的基因的常染色体隐性突变引起的，ATP8B1 是一种假定的氨基磷脂转运 P 型三磷酸腺苷酶。疾病的确切发病机制尚不清楚，目前尚无有效的药物治疗方法。在这里，我们系统地描述了与 PFIC1 和/或 BRIC1 相关的六种不同 ATP8B1 错义突变（p.L127P、p.G308V、p.D454G、p.D554N、p.I661T 和 p.G1040R）和一个无义突变（p.R1164X）的分子后果。除了 p.L127P 突变外，所有突变都导致 ATP8B1 蛋白表达明显减少，而信使 RNA 表达不受影响。七种突变中的五种导致 ATP8B1 在内质网中（部分）滞留。在 30°C 培养细胞和用蛋白酶体抑制剂处理可以部分恢复蛋白质表达，表明蛋白质错误折叠和随后的蛋白酶体降解。通过预测大多数突变对 ATP8B1 同源模型的后果，证实了蛋白质错误折叠。用临床批准的药理学伴侣 4-苯基丁酸治疗可部分恢复 G308V、D454G、D554N 和特别是 I661T 等 ATP8B1 取代物的表达和定位缺陷，这些突变是 BRIC1 中最常发现的突变。
相当大比例的 ATP8B1 突变导致在质膜上的异常折叠和表达减少。这些影响部分通过用 4-苯基丁酸治疗得到恢复。我们提出，用药理学伴侣治疗可能是改善间歇性（BRIC1）疾病患者复发性胆汁淤积发作的有效治疗策略。
