Study of the molecular mechanism in the keratin disease based on the pathological model in epidermolysis bullosa simplex with migratory circinate erythema

我们描述了日本和韩国的两个不相关的家庭，他们的患者患有一种名为EBS的独特类型的单纯大疱性表皮松解症，伴有迁移性环状红斑和角蛋白基因KRT5的新突变；即移码和延迟终止密码子与前面描述的任何亚型不一致。皮肤活检电镜显示基底细胞中角蛋白中间丝数量减少，未见张力丝结块。我们在这两种情况下都发现了一种新的杂合缺失突变（KRT5的1649delG）。这种缺失预计会产生一个突变的K5蛋白，其末端移码41个氨基酸，由于一个延迟的终止密码子，比野生型K5蛋白长35个氨基酸。在免疫组织化学和免疫印迹中，患者皮肤对识别突变型长氨基酸的特异性抗体表现出阳性反应。由于在独立家族中发现了相同的异常细长突变KRT5基因，因此预测的异常细长角蛋白可能导致从未报道过的非典型临床表型。为了进一步研究角蛋白5的功能，我们分析了角蛋白5在转基因小鼠和转染的角质细胞中的表达。转基因小鼠皮肤未表现出任何临床病理症状，但免疫印迹显示表皮中有异常的K5蛋白。在转染的角质细胞分析中，细长的K5与正常的内源性K14共定位，表明突变的K5不会破坏角蛋白丝的组装。

We described two unrelated families in Japan and Korea having patients with an unique type of epidermolysis bullosa simplex named EBS with migratory circinate erythema and a novel mutation in the keratin gene, KRT5 ; i.e., frameshift and delayed stop codon inconsistent with any subtype described before. Electron microscopy of skin biopsies showed a reduction in the number of keratin intermediate filaments in the basal cells without tonofilament clumping. We identified a novel heterozygous deletion mutation (1649delG of KRT5) in both cases. This deletion is predicted to produce a mutant K5 protein with a frameshift of its terminal 41 amino acids, and 35 amino acids longer than the wild type K5 protein due to a delayed termination codon. Patient skin show positive reactivity to specific antibody which recognize the mutant elongated amino acids both in immunohistochemistry and immunoblotting.Since the same abnormal elongated mutant KRT5 gene was found in the independent families, the predicted abnormal elongated keratin protein is likely to lead to an atypical clinical phenotype that has never been reported. Furthermore to investigate the function of elongated keratin 5 protein, keratin 5 expression in transgenic mice and transfected keratinocyte was analyzed. The transgenic mouse did not show any clinicopathological symptom on the skin, although immunoblotting showed the abnormal K5 protein in the epidermis. In the transfected keratinocyte analysis, the elongated K5 colocalized with normal endogeneous K14, suggested that mutant K5 does not disrupt keratin filament assembly.