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 approximately 130-kDa molecular mass react with antisera from patients with renal vasculitis (Kain, R., Matsui, K., Exner, M., 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 lambdagt11 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.