SS-A/Ro antigens are major autoantibody targets in patients with Sjogren's syndrome, systemic lupus erythematosus, neonatal lupus with congenital heart block, and subacute cutaneous lupus erythematosus. Human SS-A/Ro autoimmune sera that are positive in double immunodiffusion tests often recognize 2 antigenic components of 52 and 60 kD that do not show immunological cross reactivity. Recent data on human cDNAs from our laboratory showed that the 52-kD protein shared extensive homology with a subfamily of zinc finger proteins and the 60-kD protein was a member of a RNA-binding protein family. In addition, our results showed that there were at least 2 different isoforms in MOLT4 cells encoding for 2 full-length 60-kD SS-A/Ro proteins differing only at the C-terminal residues. Additional cDNA clones selected for the 60-kD component represented new mRNAs variants that might also be products of alternative mRNA splicing. A cDNA of the 52-kD SS-A/Ro protein representing an alternatively spliced form was also detected.
The specific aims are: 1. Analysis of the gene structures of human SS-A/Ro autoantigens. This includes the mapping of the exon-intron junctions, promotor elements, and defining the different transcription start sites that may result in alternative initiations and alternative mRNA splicing observed in the cDNA clones. 2. Analysis of mRNA and protein expression of SS-A/Ro in different human cell lines. This includes an examination of the changes in cellular expression and distribution of these various SS-A/Ro proteins as a result of UV-irradiation and 17beta-estradiol treatment. The realization of these aims is enhanced by the availability of specific antibodies including 5 murine monoclonal antibodies to the 60-kD SS-A/Ro protein, rabbit polyclonal antibodies raised by immunization with recombinant proteins and specific for' the 52-kD and 60-kD SS-A/Ro proteins, and rabbit anti-C-terminal peptide antibodies that are specific to each of the 2 isoforms of 60-kD SS-A/Ro. The rationale for the specific aims is to elucidate the basis for the heterogeneity of SS-A/Ro. Studies of the molecular heterogeneity of the SS-A/Ro antigens and their cellular expression may give important insights into the function of SS-A/Ro.
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