Stimulation of iNOS expression and apoptosis resistance in B-cell chronic lymphocytic leukemia (B-CLL) cells through engagement of Toll-like receptor 7 (TLR-7) and NF-kappaB activation.
B-CLL cells are characterized by in vivo resistance to apoptosis due, in part, to the presence of an inducible nitric oxide synthase, iNOS, as the NO released plays anti-apoptotic role, notably by inhibiting caspases. The mechanisms leading to spontaneous expression of iNOS in these cells are presently unknown. The restricted use of some V(H) sub-groups and the sequences of the monoclonal immunoglobulins of the B-cell receptor expressed by the leukemia cells suggested that the latter have encountered specific auto-antigens and/or microbial derived antigens. Their binding to the BCR provides an activation signal resulting in enhanced survival, hence could be involved in the aetiology of the disease. At the interface of innate and cognate immunity, Toll-like receptors, TLR, recognize PAMPs (pathogen-associated molecular patterns) expressed by various bacteria and virus as well as some self-antigens. We thus hypothesized that TLR were involved in the early steps of B-CLL oncogenesis, notably apoptosis resistance through the induction of iNOS expression and the production of NO. Our results show that B-CLL cells express TLR-7 and TLR-9. Incubation of B-CLL cells with TLR-7 agonists effectively resulted in an increased resistance to apoptosis that was reverted with the NOS inhibitor L-NMMA. This resistance was associated with enhanced iNOS expression (protein and mRNA) and NO release, stimulation of NF-kappaB activation, phosphorylation of I kappaB alpha, all these events being suppressed with wedelolactone or Bay 11-7085, two inhibitors of I kappaB alpha phosphorylation. Our present data thus suggest that TLR-7 signaling stimulates apoptosis resistance, notably through an NF-kappaB-dependent activation of the NO pathway.
Hammadi
Amar
A
UMRS 872 INSERM/Université Pierre et Marie Curie/Université Paris Descartes, Equipe 18, Centre de Recherche des Cordeliers, 15 rue de l'Ecole de Médecine, 75270 Paris cedex 06, Paris, France.
Billard
Christian
C
Faussat
Anne-Marie
AM
Kolb
Jean-Pierre
JP
D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis; D005260:Female; D015870:Gene Expression; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D016328:NF-kappa B / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000235:genetics*; D010766:Phosphorylation; D015398:Signal Transduction; D051199:Toll-Like Receptor 7 / Q000378:metabolism*; D051217:Toll-Like Receptor 9 / Q000378:metabolism
D016328:NF-kappa B; C495348:TLR7 protein, human; C495371:TLR9 protein, human; D051199:Toll-Like Receptor 7; D051217:Toll-Like Receptor 9; D009569:Nitric Oxide; C496319:NOS2 protein, human; D052247:Nitric Oxide Synthase Type II