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.
A novel cDNA, IA-2beta, 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-2beta 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-2beta. Competitive inhibition experiments showed that IDDM sera have autoantibodies that recognize both common and distinct determinants on IA-2 and IA-2beta. 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-2beta 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-2beta, 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-2beta and IA-2 are the precursors of the 37-kDa and 40-kDa islet cell autoantigens, respectively, and that both IA-2 and IA-2beta are major autoantigens in IDDM.
Lu
J
J
Laboratory of Oral Medicine, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 20892-4322, USA.
Li
Q
Q
Xie
H
H
Chen
Z J
ZJ
Borovitskaya
A E
AE
Maclaren
N K
NK
Notkins
A L
AL
Lan
M S
MS
D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000276:immunology*; D001483:Base Sequence; D003001:Cloning, Molecular; D003429:Cross Reactions; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology*; D015870:Gene Expression; D007515:Islets of Langerhans / Q000201:enzymology / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology*; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001324:Autoantigens; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010446:Peptide Fragments; D012333:RNA, Messenger; C516862:PTPRN protein, human; C102889:PTPRN2 protein, human; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; C516863:Ptprn protein, mouse; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8