title: Molecular cloning of phogrin, a protein-tyrosine phosphatase homologue localized to insulin secretory granule membranes.
abstract: An insulin granule membrane protein-tyrosine phosphatase (PTP) homologue, phogrin, was cloned by expression screening of a rat insulinoma cDNA library. The 3723-base pair cDNA encoded a transmembrane glycoprotein of 1004 amino acids (Mr 111876) that underwent post-translational proteolysis to 60-64-kDa products after a 30-min delay. The kinetics of proteolytic conversion (t1/2 = 45 min) and turnover (t1/2 = 12 h) were consistent with sorting and conversion in a late compartment of the secretory pathway. Studies on the native beta-cell protein suggested that the COOH-terminal PTP domain was on the cytosolic face of the secretory granule. The lumenal segment was comprised of a protease-resistant globular domain of around 25 kDa. Its localization and topology is thus consistent with a transmembrane receptor function related to granule biogenesis, exocytosis, or subsequent membrane recovery, and it should prove to be a useful cell biological marker for the granule membrane. High expression of the mRNA (5.4 kilobases) and protein was evident in islets, pancreatic alpha- and beta-cell tumor lines, brain cells, and other cells of neuroendocrine lineage. It is closely related to the diabetic autoantigen ICA512 (IA-2) (42% identity overall; 80% in the 260-amino acid PTP domain) and thus a potential target of autoimmunity in diabetes mellitus.
authors.affiliation: Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QR, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Wasmeier
authors.forename: J C
authors.initials: JC
authors.lastname: Hutton
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens; D001483:Base Sequence; D002451:Cell Compartmentation; D003001:Cloning, Molecular; D003594:Cytoplasmic Granules / Q000201:enzymology*; D018076:DNA, Complementary / Q000235:genetics; D007340:Insulinoma; D007425:Intracellular Membranes / Q000201:enzymology*; D007515:Islets of Langerhans / Q000201:enzymology*; D008562:Membrane Glycoproteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics*; D017027:Protein Tyrosine Phosphatases / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
chemical_list: D001324:Autoantigens; D018076:DNA, Complementary; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C516862:PTPRN protein, human; C102889:PTPRN2 protein, human; D017027:Protein Tyrosine Phosphatases; C516864:Ptprn protein, rat; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8