Interleukin-15 delays human neutrophil apoptosis by intracellular events and not via extracellular factors: role of Mcl-1 and decreased activity of caspase-3 and caspase-8.
Interleukin-15 (IL-15) induces the de novo protein synthesis of intracellular polypeptides and delays neutrophil apoptosis by a mechanism that is still unclear. Herein, we investigated the potential antiapoptotic role of newly synthesized proteins released into the external milieu in IL-15-induced neutrophils. We found that IL-15 induces the de novo synthesis of an approximately 23-kDa protein, representing the predominant protein detected in the milieu, and identified it as IL-1 receptor antagonist (IL-1Ra) by Western blot and immunoprecipitation. We quantified IL-1Ra, IL-1alpha, and IL-1beta concentrations by enzyme-linked immunosorbent assay in intracellular and extracellular fractions from IL-15-induced neutrophils and found that IL-15 does not increase IL-1alpha or IL-1beta production but induces IL-1Ra release. Also, we demonstrated that IL-1Ra does not modulate apoptosis, even at a concentration 250 times greater than that measured in the external milieu. In contrast to granulocyte macrophage-colony stimulating factor, the supernatant harvested from IL-15-induced neutrophils was devoid of antiapoptotic activity. Addition of cycloheximide demonstrates that IL-15 delays apoptosis via de novo synthesis of intracellular proteins and that it increases myeloid cell differentiation factor-1 stability. We demonstrated also that IL-15 decreases the activity of caspase-3 and caspase-8, resulting in an inhibition of vimentin cleavage. Our results indicate that IL-15 can activate an anti-inflammatory loop, based on its ability to induce the synthesis of IL-1Ra by neutrophils. We conclude that IL-15 delays human neutrophil apoptosis by intracellular events and not via extracellular factors.
Bouchard
Amélie
A
INRS-Institut Armand-Frappier, Université du Québec, Pointe-Claire, Canada.
Ratthé
Claude
C
Girard
Denis
D
D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000032:analysis; D019409:Interleukin-15 / Q000494:pharmacology*; D007700:Kinetics; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000502:physiology*; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2; D012795:Sialoglycoproteins / Q000378:metabolism
C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D019409:Interleukin-15; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012795:Sialoglycoproteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases