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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) polymerase (PARP) and to assess the significance of autoantibodies to the 2 zinc fingers of this enzyme in patients with autoimmune rheumatic and bowel diseases.


METHODS
The specificity of antienzyme autoantibodies was established by dot immunoassay with recombinant human PARP and by enzyme-linked immunosorbent assay using the recombinant N-terminal 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 (and mutated peptides) corresponding to zinc-finger motifs F1 and F2 that are present in the DNA binding domain, zinc fingers from other self antigens (e.g., peptides from Ro60, Ro52, and U1C proteins), and poly(ADP-ribose). Sera from patients with autoimmune rheumatic and bowel diseases were tested, as were affinity-purified antibodies. Histocompatibility typing of systemic lupus erythematosus (SLE) patients was performed 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 F1 and F2 represented immunodominant targets for IgG antibodies 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 F1 and F2, which contain mutations at the cysteine residues involved in zinc coordination. F1/F2 antibodies did not cross-react with zinc fingers from other self proteins. No correlation was found between the presence of F1/F2 autoantibodies in SLE sera and the presence of other autoantibodies typical of this disease (e.g., anti-double-stranded DNA and poly[ADP-ribose] antibodies). The presence of F2 antibodies in the serum 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 "execution phase" of apoptosis. The high prevalence in certain autoimmune rheumatic and bowel diseases of antibodies to F1 and F2, which are directly involved in this process, is further evidence implicating involvement of the DNA repair system in chronic inflammatory diseases.