Post-transcriptional regulation of inducible nitric oxide in chronic lymphocytic leukemia B cells in pro and antiapoptotic culture conditions

Functional inducible NOS(INOS) may be involved in the prolonged lifespan of chronic lymphocytic leukemia cells (B-CLL), although the exact mechanisms implicated remain elusive as yet. In this work, we have examined INOS expression in normal B lymphocytes and B-CLL in pro and antiapoptotic conditions. Our results demonstrate: 1) The existence of a new splice variant charaterized by a complete deletion of exon 14 (INOS 13-16) which was preferentially detected in normal B lymphocytes and may represent an isoform that could be play a role in the regulation of enzyme activity. 2) The existence of another alternatively spliced INOS mRNA transcript involving a partial deletion of the flavodoxin region (INOS 13-16) was correlated to a decreased B-Cll cell viability. The 9-B-D arabinofuranosyl-2-fluoradenine or fludarabine (F-ara) treatment induced INOS 13-16) and the expression of a 122kDa INOS protein. These results suggest that in B-CLL, a regulation process involving nitric oxide (NO) levels could occur by a post-transcriptional mechanism mediated by soluble factors. Our results also provide an insight into a new complmentary proapoptotic action of F-ara in B-CLL by the induction of particular INOS splice variants, leading to the activation of a caspase-3-dependent apoptotic pathway

Peroxynitrite inhibits T lymphocyte activation and proliferation by promoting impairment of tyrosine phosphorylation and peroxynitrite-driven apoptotic death

Peroxynitrite (ONOO-) is a potent oxidizing and nitrating agent produced by the reaction of nitric oxide with superoxide. It readily nitrates phenolic compounds such as tyrosine residues in proteins, and it has been demonstrated that nitration of tyrosine residues in proteins inhibits their phosphorylation. During immune responses, tyrosine phosphory lation of key substrates by protein tyrosine kinases is the earliest of the intracellular signaling pathways folowing activation through the TCR complex. This work was aimed to evaluate the effects of ONOO- on lymphocyte tyrosine phosphorylation, proliferation, and survival. Additionally, we studied the generation of nitrating species in vivo and in vitro during immune activation. Our results demonstrate that ONOO-, through nitration of tyrosine residues, is able to inhibit activation-induced protein tyrosine phosphorylation in purified lymphocytes and prime them to undergo apoptotic cell death after PHA- or CD3-mediated activation but non upon phorbol ester.mediated stimulation. We also provide evidence indicating that peroxynitrite is produced during in vitro immune activation, mainly by cell of the monocyte/macrophage lineage. Furthermore, immunohistochemical studies demonstrate the in vivo generation of nitrating species in human lymph nodes undergoing mild to strong immune activation. Our results point to a physiological role for ONOO- as a down-modulator of immune responses and also as key mediator in cellular and tissue injury associated with chronic activation of the immune system