Molecular cloning,expression,and chromosomal localization of a human tubulointerstitial nephritis antigen

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Tubulointerstitial nephritis antigen (TIN-ag) is an extracellular matrix base ment protein which was originally identified as a target antigen involved in anti-tubular basement membrane (TBM) antibody-mediated interstitial nephritis(TIN). Further investigations elucidated that TIN-ag plays a role in renal tubulogenesis and that TIN-ag is defected in hereditary tubulointerstitial disorder such as juvenile nephronophthisis. We previously isolated and characterized 54 dKa glycoprotein as TIN-ag. cDNA encoding rabbit and mouse TIN-ag has recently been identified. In the present study, the cDNA of the human honologue of TIN-ag was cloned and its nucleotid sequence was determined (accession No.AB022277, the DDBJ nucleotide sequence database). Deduced amino acid sequence (476aa) exhibited the presence of a signal peptide (1-18aa), cysteine residues termed follistatinmodule, six potential glycosylation sites, and an ATP/GTP-binding site. Homology search revealed 〜 85% homology with both rabbit and mouse TIN-ag, and also some (〜40%) similarity with C. elegans. Human TIN-ag contained a sequence similar to several classes of extracelular matrix molecules in amino terminal region and to cathepsin family of cysteine proteinases in the carboxyl terminal region. Northern blot analysis revealed exclusive expression of this molecule in human adult and fetal kidney tissues. Using a monoclonal antibody recognizing human TIN-ag, protein expression (〜50 kDa) was identified in cultured COS-1 cells transfected with human TIN-ag cDNA. The human TIN-ag was mapped to chromosome 6p11. 2-12 by fluorescence in situ hybridization. These results may privide further evidence for understanding TIN-ag molecule and clues for gene analysis of juvenile nephronophthisis.