Polyamine-fas interactions: Inhibition of polyamine biosynthesis in MRL-lpr/lpr mice is associated with the up-regulation of fas mRNA in thymocytes

MRL-lpr/lpr is a strain of mice that develops spontaneous signs of the auto immune disease, systemic lupus erythematosus (SLE or lupus), The lpr (lymph oproliferation) defect has been identified as an insertion of an early tran sposon (ETn) derived sequence into the fas apoptosis gene. We studied the i n vivo effects of difluoromethlornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme, ornithine decarboxylase (ODC), on the expression of fas in MRL-lpr/lpr mice as well as in congenic MRL-+/+ and a utoimmune NZB/W strains. Using Northern blot hybridization and reverse tran scription polymerase chain reaction (RT-PCR), we found that DFMO treatment resulted in an increase in the expression of fas mRNA in the thymus of MRL- lpr/lpr mice. Using RT-PCR, we further found that the increased expression of fas was associated with the suppression of chimeric ETn/fas mRNA. With f ractionated CD4(+) and CD8(+) T cells, we found a cell-specific effect of D FMO on chimeric ETn/fas expression in CD8+ cells. ETn/fas expression was de tected in CD8(+) T cells from untreated mice, but it was eliminated after D FMO treatment. HPLC analysis of polyamines showed depletion of putrescine a nd partial reduction of spermidine (35%) in DFMO-treated mice compared to c ontrols. These results indicate that DFMO-mediated polyamine depletion is l inked to the regulation of fas and chimeric ETn/fas in MRL-lpr/lpr mice. El evated le, els of polyamines in this strain, as found in earlier studies, m ay be associated with the progression of the autoimmune disease by altering the expression of fas gene or by facilitating the expression of chimeric E Tn/fas. Our data also provide new mechanistic insights into the beneficial effects of DFMO an these mice.