Goseki-Sone M, Orimo H, Iimura T, Miyazaki H, Oda K, Shibata H, Yanagishita M, Takagi Y, Watanabe H, Shimada T, Oida S
Department of Food and Nutrition, Japan Women's University, Tokyo, Japan.
J Bone Miner Res. 1998 Dec;13(12):1827-34. doi: 10.1359/jbmr.1998.13.12.1827.
Hypophosphatasia (HOPS) is an inherited disorder characterized by defects in skeletal mineralization due to the deficiency of tissue-nonspecific alkaline phosphatase (TNSALP). To date, various mutations in the TNSALP gene have been identified. Especially, a deletion of T at position 1735 (1735T-del) located in exon 12 has been detected in three genetically unrelated Japanese patients, which seems to be one of the hot spots among the causative mutations in Japanese HOPS patients. 1735T-del causes a frame shift downstream from codon 503 (Leu), and consequently the normal termination codon at 508 is eliminated. Since a new inframe termination codon appears at codon 588 in the mutant DNA, the resultant protein is expected to have 80 additional amino acids. Expression of the mutant TNSALP gene using COS-1 cells demonstrated that the protein translated from the mutant 1735T-del had undetectable ALP activity, and its molecule size was larger than normal, as expected. Interestingly, an immunoprecipitation study of patients' sera using antibody against TNSALP revealed an abnormal protein which corresponded in size to the mutated TNSALP expressed by COS-1 cells, suggesting that the abnormal TNSALP is made by HOPS patients. The detection of TNSALP in cells transfected with 1735T-del using an immunofluorescent method exhibited only a faint signal on the cell surface, but an intense intracellular fluorescence after permeabilization.
低磷酸酯酶症（HOPS）是一种遗传性疾病，其特征是由于组织非特异性碱性磷酸酶（TNSALP）缺乏导致骨骼矿化缺陷。迄今为止，已在TNSALP基因中鉴定出各种突变。特别是，在三名无亲缘关系的日本患者中检测到位于外显子12的第1735位（1735T-del）的T缺失，这似乎是日本HOPS患者致病突变中的热点之一。1735T-del导致从密码子503（Leu）下游发生移码，因此消除了508位的正常终止密码子。由于在突变DNA的密码子588处出现了一个新的框内终止密码子，预计所得蛋白质将多80个氨基酸。使用COS-1细胞表达突变的TNSALP基因表明，从突变体1735T-del翻译的蛋白质具有不可检测的碱性磷酸酶（ALP）活性，并且其分子大小比正常的大，正如预期的那样。有趣的是，使用抗TNSALP抗体对患者血清进行免疫沉淀研究发现了一种异常蛋白质，其大小与COS-1细胞表达的突变TNSALP相对应，这表明异常的TNSALP是由HOPS患者产生的。使用免疫荧光方法在转染了1735T-del的细胞中检测TNSALP，结果显示在细胞表面仅出现微弱信号，但在透化后细胞内有强烈荧光。
