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Br J Haematol. 1997 Dec;99(3):481-9.

Induction of nitric oxide synthase is involved in the mechanism of Fas-mediated apoptosis in haemopoietic cells.

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1
Division of Haematology, Federico II University Medical School, Naples, Italy.

Abstract

Induction of nitric oxide synthase (iNOS) and production of the toxic metabolite nitric oxide (NO) is one of the interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) regulated effector mechanisms that can lead to apoptosis of haemopoietic progenitor cells. Fas-receptor (Fas-R) expression can be stimulated by IFN-gamma and TNF-alpha. Transactivation of iNOS, and possibly Fas-R promoters, by interferon regulatory factor-1 expressed in response to IFN-gamma may be a part of the iNOS transduction pathway. We investigated whether the effects of Fas-R triggering in haemopoietic cells were mediated by NO. On Western blotting, we observed that Fas-receptor agonist, monoclonal antibody CH11. enhanced expression of iNOS. As shown by the reverse transcription polymerase chain reaction. CH11 also induced iNOS mRNA expression in purified CD34+ cells. To determine whether NO was involved in Fas-mediated apoptosis we inhibited iNOS-catalysed production of NO using anti-sense (AS) oligodeoxynucleotides (ODN) directed against iNOS mRNA. After culture of haemopoietic cells in the presence of AS-ODN, iNOS expression decreased and was no longer enhanced by Fas. This effect was associated with the prevention of Fas-mediated apoptosis, as determined by a DNA fragmentation and terminal deoxynucleotidyl transferase staining. In colony assays, specific AS-oligonucleotides prevented FAS-mediated inhibition of colony formation by total bone marrow and CD34+ progenitor cells. Our data suggest that the inhibitory effects of Fas, including induction of apoptosis, are mediated by effector mechanisms that may be similar to those described for IFN-gamma and TNF-alpha.

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