@article{7a59cfd6d05540dea231c47f6694d092,
title = "Polyamine-fas interactions: Inhibition of polyamine biosynthesis in MRL-lpr/lpr mice is associated with the up-regulation of fas mRNA in thymocytes",
abstract = "MRL-lpr/lpr is a strain of mice that develops spontaneous signs of the autoimmune disease, systemic lupus erythematosus (SLE or lupus). The lpr (lymphoproliferation) defect has been identified as an insertion of an early transposon (ETn) derived sequence into the fas apoptosis gene. We studied the in vitro effects of difluoromethylornithine (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 autoimmune NZB/W strains. Using Northern blot hybridization and reverse transcription 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 fractionated CD4+ and CD8+ T cells, we found a cell-specific effect of DFMO on chimeric ETn/fas expression in CD8+ cells. ETn/fas expression was detected in CD8+ T cells from untreated mice, but it was eliminated after DEMO treatment. HPLC analysis of polyamines showed depletion of putrescine and partial reduction of spermidine (35%) in DFMO-treated mice compared to controls. These results indicate that DFMO-mediated polyamine depletion is linked to the regulation of fas and chimeric ETn/fas in MRL-lpr/lpr mice. Elevated levels of polyamines in this strain, as found in earlier studies, may be associated with the progression of the autoimmune disease by altering the expression of fas gene or by facilitating the expression of chimeric ETn/fas. Our data also provide new mechanistic insights into the beneficial effects of DFMO on these mice.",
keywords = "Difluolomethylornithine, ETn, Fas, MRL-lpr/lpr mice, Polyamines",
author = "Hsu, {Hui Chen} and Thresia Thomas and Sigal, {Leonard H.} and Thomas, {T. J.}",
note = "Funding Information: Several previous studies have shown that polyamines might interfere with specific gene regulation. For example, polyamine-mediated up-regulation of c-myc and c-fus has been reported at the transcriptional Polyamines have also been shown to suppress the transcription of their own biosynthetic enzymes, ODC and SAMDC, as a feedback ~ o n t r o l . [ ~ *T,hey~ ]may also up-regulate the transcription of their catabolic enzyme, spermidine/spermine acetyl transferase (SSAT).[”] Thomas and Thomas[271 reported that DFMO treatment attenuated the degradation of cydin B1 mRNA. Flescher et ul.[5{\textquoteright}35r2e1p orted that increased level of polyamines down-regulated IL-2 production by interfering with mitogen-induced transmembrane signaling, as well as by inhibiting the expression and the DNA binding activity of transcription factors. Thus, polyamines may also regulate fus transcripts in MRL-lpr/lpr mice through mechanisms independent of their action on ETn. In addition to tissue-and strain-specific differences in fus expression, our data also show cell-specific differences in the regulation offus and ETn in CD4+ and CD8{\textquoteright} subpopulations ofT cells. Previous studies suggested differential expression of fus in T cell subset^.{"}',^',^^^. On the other hand, the integration offus gene leads to cell-specific expression during T cell differentiation.“ {\textquoteleft}I For example, replacement of normal fas gene in MRL-lpr/lpr mice not only increased the expression of fus in double positive and single positive T cells, but also significantly decreased the expansion of double negative T cells and increased the proportion of double positive T cells in thymus.“ Our previous studies[301sh owed that DFMO treatment decreased the abnormal expansion of double negative T cells and increased the percentages of double positive T cells and single positive CD8+ T cells in the thymus of MRL-lpr/lpr mice, substantiating a differential role of polyamines in CD4+/CD8+ T cells of this strain. Thus, cell-specific expression of fus could be manipulated by altering in vivn polyamine levels. In summary, a link between polyamines and the steady-state level of fus and ETnLfbs transcripts was found in the thymus of MRL-lpr/lpr mice. Although the lpr phenotype is due to a mutation of jbs caused by the insertion of ETn, the regulation of these transcripts within the microenvironment of thymus is not clear. Our results suggest a role of polyamines in cell-specific mRNA splicing in the ETnLfbs region. It would be interesting to determine whether the depletion of polyamines using DFMO treatment may enhance the susceptibility to anti- ,fus or activation-induced cell death in MRL-lpr/lpr mice or whether the replenishment of polyamines through exogenous sources would abrogate the effect of DFMO on the expression of ,fhs or Etn/ ,fas in MRL-lpr/lpr mice. Future investigations on these lines may provide new insights into the role of polyamines in murine lupus caused by the,fus gene defect. This work was supported, in part, by grants from the New Jersey Chapter of the Arthritis Foundation and The American Lupus Society.",
year = "1999",
doi = "10.3109/08916939908994750",
language = "English (US)",
volume = "29",
pages = "299--309",
journal = "Autoimmunity",
issn = "0891-6934",
publisher = "Informa Healthcare",
number = "4",
}