Identification of a second transmembrane protein tyrosine phosphatase, IA-2beta, as an autoantigen in insulin-dependent diabetes mellitus: precursor of the 37-kDa tryptic fragment.

Abstract

A novel cDNA, IA-2p, was isolated from a mouse neonatal brain library. The predicted protein sequence revealed an extracellular domain, a transmembrane region, and an intracellular domain. The intracellular domain is 376 amino acids long and 74% identical to the intracellular domain of IA-2, a major autoantigen in insulin-dependent diabetes mellitus (IDDM). A partial sequence of the extracellular domain of IA-2p8 indicates that it differs substantially (only 26% identical) from that of IA-2. Both molecules are expressed in islets and brain tissue. Forty-six percent (23 of 50) of the IDDM sera but none of the sera from normal controls (0 of 50) immunoprecipitated the intracellular domain of IA-2,3. Competitive inhibition experiments showed that IDDM sera have autoantibodies that recognize both common and distinct determinants on IA-2 and IA-213. Many IDDM sera are known to immunoprecipitate 37-kDa and 40-kDa tryptic fragments from islet cells, but the identity of the precursor protein(s) has remained elusive. The current study shows that treatment of recombinant IA-2p and IA-2 with trypsin yields a 37-kDa fragment and a 40-kDa fragment, respectively, and that these fragments can be immunoprecipitated with diabetic sera. Absorption of diabetic sera with unlabeled recombinant IA-2 or IA-2f8, prior to incubation with radiolabeled 37-kDa and 40-kDa tryptic fragments derived from insulinoma or glucagonoma cells, blocks the immunoprecipitation of both of these radiolabeled tryptic fragments. We conclude that IA-2,8 and IA-2 are the precursors of the 37-kDa and 40-kDa islet cell autoantigens, respectively, and that both IA-2 and IA-2p8 are major autoantigens in IDDM.

IA-2-autoantibodies complement GAD 65 -autoantibodies in new-onset IDDM patients and help predict impending diabetes in their siblings

“…Interestingly, this individual was negative for IAA and GAD 65 -Ab, but was strongly ICA positive suggesting that other autoantibodies besides GAD 65 -Ab, IA-2-Ab or IAA must also contribute to ICA. In this respect, the IA-2b PTP-ase may represent an additional relevant islet cell autoantigen [1].…”

“…Interestingly, this individual was negative for IAA and GAD 65 -Ab, but was strongly ICA positive suggesting that other autoantibodies besides GAD 65 -Ab, IA-2-Ab or IAA must also contribute to ICA. In this respect, the IA-2b PTP-ase may represent an additional relevant islet cell autoantigen [1].In conclusion, IA-2-Ab are IDDM markers with a high diagnostic specificity, which complement GAD 65 -Ab and help predict impending IDDM in siblings of patients. In combination with other molecular autoantibody assays such as IAA and GAD 65 -Ab, IA-2-Ab may replace ICA testing for IDDM prediction in the future.…”

“…Two structurally related transmembrane PTPases, IA-2 (homologous to ICA512) and IA-2b, have recently been characterized as autoantigens in insulin-dependent diabetes mellitus (IDDM) [1]; they represent the precursor forms of the previously described 37/40 kDa tryptic fragments of islet cell membrane proteins which are recognized by circulating immunoglobulins from IDDM patients [1][2][3].…”

“…During the past few years, molecular cloning has identified a family of intracellular and transmembrane proteins with protein tyrosine phosphatase (PTPase)-activity which are believed to play a role in intracellular and intercellular signal transduction [1]. Two structurally related transmembrane PTPases, IA-2 (homologous to ICA512) and IA-2b, have recently been characterized as autoantigens in insulin-dependent diabetes mellitus (IDDM) [1]; they represent the precursor forms of the previously described 37/40 kDa tryptic fragments of islet cell membrane proteins which are recognized by circulating immunoglobulins from IDDM patients [1][2][3].…”

Anti-pancreatic autoimmunity and Graves' disease: study of a cohort of 600 Caucasian patients

“…Antibodies to glutamic acid decarboxylase (GAD)/64 kDa protein have also been detected in diabetic and non-diabetic endocrine patients (7)(8)(9)(10). More recently, the predictive value of 37/40 kDa antibodies, identified as IA2 and phogrin proteins (11)(12)(13)(14)(15), has been reported in nondiabetic patients with organ-specific autoimmune disease (16). Very few of these studies previously published on anti-pancreatic immunity in Caucasian endocrine patients, were homogeneous with regard to the initial disease and the intensity of extra-pancreatic autoimmunity at the time of sampling and studied the whole range of humoral markers available.…”