The point mutation of polymeric immunoglobulin receptor and IgA nephropathy

比较健康人和IgA肾病（IgAN）患者外周血样本的基因组DNA序列发现，在IgA肾病患者中，在多聚免疫球蛋白受体（pIgR）DNA中检测到高分DNA突变。该突变主要发生在580位氨基酸处，导致丙氨酸被缬氨酸取代。本研究的目的是比较野生型和突变型pIgR（A580 V）分子的生化特性，并阐明这种突变与IgAN的相关性。将两种cDNA引入哺乳动物表达载体中并用于转染。通过代谢标记或表面生物素化方法标记两种转染子。标记后，估计培养基中释放的游离分泌组分（fSC ; pIgR的细胞外部分）的量。然而，野生型和突变型之间没有观察到差异。已知在位置606和607的谷氨酸在几种动物物种之间是保守的，并且被认为是pIgR的细胞外部分的切割位点。通过用定点诱变将这两个残基取代为丙氨酸残基，我们检查了这些变化对fSC释放的影响。结果，未观察到变化。这些结果表明pIgR的酶切可能是差异的。控制在上皮细胞和成纤维细胞之间。

Comparison of the genomic DNA sequences of the peripheral blood samples taken from healthy individuals and IgA-nephropathy (IgAN) patients has revealed that, in IgAN-patients, high-score DNA mutation was detected in polymeric immunoglobulin receptor (pIgR) DNA. The mutation was frequently detected at the position of 580 aa and resulted in the substitution of alanine to valine residue. The aim of this study was to compare the biochemical properties of wild type and mutant pIgR (A580V) molecules and to elucidate the correlation of this mutation to IgAN. Both cDNA was introduced into mammalian expression vector and used for transfection. Both transfectants were labeled by metabolic labeling or surface biotinylation methods. After labeling, the amount of free secretory component (fSC ; the extracellular part of pIgR) released in the culture medium was estimated. However, no differences were observed between wt and mutant. The glutamic acid in the positions 606 and 607 were known to be conserved between several animal species and thought to be a cleaving site of the exrtracellular portion of pIgR. By substituting these two residues to alanine residue with site-directed mutagenesis, we examined the influence of these changes on the release of fSC. As results, no changes were observed. These results suggested that enzymatic cleavage of pIgR might be differentially. controlled between epithelial and fibroblastic cells.