Bachmann M, Tröster H, Bartsch H, Grölz D
Institut für Physiologische Chemie, Johannes Gutenberg Universität Mainz, Mainz, Germany.
J Autoimmun. 1996 Dec;9(6):747-56. doi: 10.1006/jaut.1996.0097.
A hot spot region was identified in the exon 7 of the nuclear autoantigen La (SS-B). Two La cDNAs were identified which contained a frame shift mutation in the hot spot region. One La cDNA was isolated from a cDNA library made from peripheral blood lymphocytes of an autoimmune patient with primary Sjögren's Syndrome, the other La cDNA was isolated from a human liver cDNA library. The patient's La cDNA had a deletion and the liver La cDNA had an insert of an (A)-residue at the same position. Inserts of 4, 16 and 24 more or less homogeneous (A)-residues were found at the same site in the three La retropseudogenes. The hot spot region located in one of the major autoepitope regions of the La antigen. Both frame shift mutations resulted in premature stop codons. In case of the human liver La cDNA, the premature stop codon located a single amino acid downstream of the frame shift mutation, while it located eleven amino acids downstream of the frame shift mutation in the patient's La cDNA. In consequence, only the sequence of the La peptide encoded by the patient's La cDNA markedly differed from the corresponding La peptide sequence. Translation of the patient's mutant La mRNA in transfected mouse cells resulted in a C-terminally truncated La peptide. Due to the lack of the nuclear location signal it remained in the cytoplasm. The modified La peptide shared homology with (i) La protein itself and (ii) a series of DNA binding proteins including other autoantigens and viral proteins such as topoisomerase I, RNA dependent RNA polymerase of influenza virus and reverse transcriptase. The self-homology region includes the amino acids which the La protein shares with B1 Laminin. It represents a putative neo-epitope that could be involved in triggering of the autoimmune response.
在核自身抗原La（SS - B）的第7外显子中鉴定出一个热点区域。鉴定出两个La cDNA，它们在热点区域含有移码突变。一个La cDNA是从一名患有原发性干燥综合征的自身免疫患者外周血淋巴细胞构建的cDNA文库中分离得到的，另一个La cDNA是从人肝脏cDNA文库中分离得到的。患者的La cDNA有一个缺失，而肝脏La cDNA在相同位置有一个（A）残基的插入。在三个La反转录假基因的相同位点发现了4、16和24个或多或少均一的（A）残基插入。热点区域位于La抗原的主要自身表位区域之一。两个移码突变均导致提前终止密码子。就人肝脏La cDNA而言，提前终止密码子位于移码突变下游一个氨基酸处，而在患者的La cDNA中，它位于移码突变下游11个氨基酸处。因此，只有患者的La cDNA编码的La肽序列与相应的La肽序列明显不同。将患者的突变La mRNA在转染的小鼠细胞中进行翻译，产生了一个C末端截短的La肽。由于缺乏核定位信号，它留在了细胞质中。修饰后的La肽与（i）La蛋白本身以及（ii）一系列DNA结合蛋白具有同源性，这些蛋白包括其他自身抗原和病毒蛋白，如拓扑异构酶I、流感病毒的RNA依赖性RNA聚合酶和逆转录酶。自身同源区域包括La蛋白与B1层粘连蛋白共有的氨基酸。它代表了一个可能参与触发自身免疫反应的假定新表位。
