ZINC IS AN ESSENTIAL COFACTOR FOR RECOGNITION OF THE DNA-BINDING DOMAIN OF POLY(ADP-RIBOSE) POLYMERASE BY ANTIBODIES IN AUTOIMMUNE RHEUMATIC AND BOWEL DISEASES

Objective. To characterize autoantibody response to poly(ADP-ribose) p olymerase (PARP) and to assess the significance of autoantibodies to t he 2 zinc fingers of this enzyme in patients with autoimmune rheumatic and bowel diseases, Methods. The specificity of antienzyme autoantibo dies was established by dot immunoassay with recombinant human PARP an d by enzyme-linked immunosorbent assay using the recombinant N-termina l fragment containing the DNA binding domain of PARP, the recombinant C-terminal catalytic domain (40-kd fragment), a peptide containing the nuclear localization signal (NLS) of PARP, 2 synthetic peptides land mutated peptides) corresponding to zinc-finger motifs F1 and F2 that a re present in the DNA binding domain, zinc fingers from other self ant igens (e.g., peptides from Ro60, Ro52, and U1C proteins), and poly(ADP -ribose), Sera from patients with autoimmune rheumatic and bowel disea ses were tested, as were affinity-purified antibodies. Histocompatibil ity typing of systemic lupus erythematosus (SLE) patients was performe d by serology. Results, Antibodies from the patient sera reacted only weakly with the recombinant N- and C-terminal domains and with the NLS peptide. In contrast, the 2 synthetic peptides corresponding to zinc- finger motifs Fl and F2 represented immunodominant targets for IgG ant ibodies from patients with SLE, mixed connective tissue disease (MCTD) , Crohn's disease, and ulcerative colitis. The sera from patients with SLE and MCTD showed much weaker reactivity with mutant peptides Fl an d F2, which contain mutations at the cysteine residues involved in zin c coordination. F1/F2 antibodies did not cross-react with zinc fingers from other self proteins, No correlation was found between the presen ce of F1/F2 autoantibodies In SLE sera and the presence of other autoa ntibodies typical of this disease (e.g., anti-double-stranded DNA and poly[ADP-ribose] antibodies). The presence of F2 antibodies in the ser um of SLE patients was negatively associated with HLA-DR6. Conclusion. An autoimmune response to PARP is potentially important because this enzyme is involved in DNA repair and is rapidly cleaved during the ''e xecution phase'' of apoptosis, The high prevalence in certain autoimmu ne rheumatic and bon el diseases of antibodies to F1 and F2, which are directly involved in this process, is further evidence implicating in volvement of the DNA repair system in chronic inflammatory diseases.