Molecular Cloning and Identification of a Receptor-Type Protein Tyrosine Phosphatase, IA-2, from Human Insulinoma

Abstract

A novel 3.6-kb cDNA, IA-2, with a 2,937-bp open reading frame was isolated from a human insulinoma subtraction library (ISL-153). The predicted amino acid sequence and in vitro-translated product of IA-2 cDNA revealed a 979-amino-acid protein with a pI value of 7.09 and a molecular mass of 105,847 daltons. The protein sequence is consistent with a signal peptide, an extracellular domain, a transmembrane region, and an intracellular domain. The extracellular domain contains an unusual cysteine-rich region following the signal peptide. The intracellular cytoplasmic domain of IA-2 possesses highly conserved regions similar to the catalytic domains found in members of the protein tyrosine phosphatase (PTP) family. Northern blot analysis showed that IA-2 mRNA was expressed in five of five freshly isolated human insulinomas, rat and mouse insulinoma cell lines, and enriched normal mouse islets. It also was found in normal human brain, pituitary, pancreas, and brain tumor cell lines, but not in a variety of other normal or tumor tissues. Based on the sequence and expression data, it appears that IA-2 is a new member of the receptor-type PTP family that is expressed in islet and brain tissues.

Peptide mapping and characterisation of glycation patterns of the glima 38 antigen recognised by autoantibodies in Type I diabetic patients

“…It is synthesised as a M r 105 000 core protein, which undergoes glycation resulting in a mobility corresponding to M r 120 000 on SDS-gels [6,8,31]. The carbohydrate moiety in glima 38 does not, however, seem to contribute to the autoreactive epitopes in the molecule [7].…”

Regulation of the diabetes-associated autoantigen IA-2 in INS-1 pancreatic beta-cells.

“…Recently, one member of the receptortype protein tyrosine phosphatase (PTP) family, designated as IA-2 or ICA512, has been identified as a major diabetes-specific autoantigen (1)(2)(3). Autoantibodies to IA-2 were observed in 50-70% of newly diagnosed patients with type 1 diabetes (4,5) and in 49-64% of prediabetic subjects at high risk for rapid development of the disease (6)(7)(8).…”

“…In the pancreatic ␤-cells, IA-2 is localized in the membrane of insulin secretory vesicles, suggesting that it may be important for maturation or trafficking of insulin granules (12). IA-2 is characterized by an intracytoplasmic domain containing 1 PTP motif, 1 transmembrane region, and an extracytoplasmic part directed to the luminal site of the insulin granula that harbor the receptor-like domain (1,12). Thus far, no enzymatic activity has been detected using common PTP substrates, and no ligand has been identified interacting with the receptor-like domain of IA-2 (13).…”

The GABA network and the pathogenesis of IDDM

“…Risk is also conferred by various non-MHC background genes [13]. As judged from IDDM-specific serum autoantibodies [14], the major autoantigens of the beta cell include glutamic acid decarboxylase (GAD) [15,16], insulin [17], and a molecule called islet cell antigen 512 [18,19] or IA-2 [20], which is probably a protein tyrosine phosphatase corresponding to the 37/40 kDa autoantigen [21,22]. Overall, anti-GAD is the most frequent autoimmune reactivity in IDDM [15,23], and, together with anti-ICA512, accounts for most of the islet cell antibodies (ICA) demonstrable by immunofluorescence [19].…”