Molecular cloning and expression of a novel human trans-Golgi network glycoprotein, TGN51, that contains multiple tyrosine-containing motifs

Previously, it has been shown that glycoproteins with similar to 130-kDa molecular mass react with antisera from patients with renal vasculitis (Kain, R., Matsui, K.,, Exner, Wi., Binder, S.,, Schaffner, G.;,, Sommer, E., M., and Kerjaschki, D., (1995) J., Exp, Med, 181, 585-597), To search for a molecule that reacts with the antibodies, we screened a lambda gt11 human placental cDNA library, Two of the isolated clones were found to encode a putative counterpart of the rodent trans-Golgi network (TGN) glycoprotein 38, hTGN46, which has the tyrosine containing motif YQRL shared by mouse and rat TGN38. Moreover, reverse transcription-polymerase chain reaction analysis of hTGN46 transcripts and genomic analysis of a cDNA deposited as an expressed sequence tag in dbEST Data Base revealed that additional cDNAs exist that are produced by alternate usage of 3'-splice sites of intron III, Alternative splicing results in frame shifts and leads to novel larger translation products with one (for hTGN48) or two (for hTGN51) additional tyrosine-containing motifs, hTGN51 expressed in Chinese hamster ovary cells were localized to the trans-Golgi network, overlapping with beta-1,4-galactosyltransferase even after mutating the tyrosine-containing motif common to hTGN46. In contrast, mutated hTGN48 and hTGN46 are no longer retrieved to the TGN, These results strongly suggest that hTGN51 may have a unique function compared with hTGN46 or hTGN48 in shuttling between the cell surface and the TGN.