APOPTOSIS IN RHEUMATOID-ARTHRITIS - P53 OVEREXPRESSION IN RHEUMATOID-ARTHRITIS SYNOVIUM

DNA damage induces p53 tumor suppressor gene expression and protein pr oduction, which in turn facilitates DNA repair or apoptosis. Wild-type p53 protein has a short half-fife, so it is rarely detected in non-ne oplastic tissue. Because DNA fragmentation is abundant in the intimal lining in rheumatoid arthritis (RA) synovial tissue (ST) using in situ end-labeling (Firestein GS, Yeo M, Zvaifler NJ: Apoptosis in rheumato id arthritis synovium. J Clin Invest 1995, 96:1631-1638), we assessed ST p53 expression. Immunohistochemical analysis of fixed RA synovium u sing antibody PAb 1801 showed prominent p53 staining in the cytoplasm and nuclei of intimal fitting cells, Noninflammatory and osteoarthriti s (COA) ST bad significantly less p53 in the lining. These data were c onfirmed by Western blot analysis of ST extracts, with abundant p53 fo und in RA compared with OA. p53 expression in cultured fibroblast-like synoviocytes (FLS) was then examined, Flow cytometry on permeabilized cells showed that RA FLS constitutively express p53 protein, Western blots showed that RA FLS expressed significantly more p53 than either OA FLS or dermal fibroblasts. Immunohistochemistry of FLS cultured in chamber slides localized the p53 to the cytoplasm of most resting FLS, with nuclear staining in only 10.7+/-2.4%. Exposure to hydrogen perox ide for increased nuclear staining to 70.7+/-12.8% after 8 hours (P=0. 003). These data indicate that p53 is overexpressed in RA ST in the in timal lining, which is the primary site of DNA damage, and is constitu tively expressed by FLS.