ISLET-CELL AUTOANTIGEN 69-KD (ICA69) - MOLECULAR-CLONING AND CHARACTERIZATION OF A NOVEL DIABETES-ASSOCIATED AUTOANTIGEN

We have identified a novel 69-kD peptide autoantigen (ICA69) associate d with insulin-dependent diabetes mellitus (IDDM) by screening a human islet lambdagt11 cDNA expression library with cytoplasmic islet cell antibody positive sera from relatives of IDDM patients who progressed to the overt disease. The deduced open reading frame of the ICA69 cDNA predicts a 483-amino acid protein. ICA69 shows no nucleotide or amino acid sequence relation to any known sequence in GenBank, except for t wo short regions of similarity with BSA. The ICA69 cDNA probe hybridiz es with a 2-kb mRNA in poly(A+ ) RNA from human pancreas, brain, heart , thyroid, and kidney, but not with skeletal muscle, placenta, spleen, or ovary. Expression of ICA69 was also detected in beta cells and cel l lines, as well as in tumoral tissue of islet cell origin. The native ICA69 molecule migrates to 69 kD in SDS-PAGE as detected with specifi c antibodies. Serum samples from relatives of IDDM patients specifical ly reacted with affinity-purified recombinant ICA69 on Western blottin g. The structural gene for ICA69 was designated ICA]. A homologue in t he mouse, designated Ica-1 was mapped to the proximal end of chromosom e 6 (within 6 cM of the Met protooncogene). ICA69 adds a novel autoant igen to the family of identified islet target molecules. and by the ma nner of its identification and characterization large amounts of antig en are available for development of quantitative, convenient predictiv e assays for autoantibodies and analysis of the role of this molecule in diabetes autoimmunity, as well as its physiologic function.