Induction of Bim limits cytokine-mediated prolonged survival of neutrophils.
Under inflammatory conditions, neutrophil apoptosis is delayed due to survival-factor exposure, a mechanism that prevents the resolution of inflammation. One important proinflammatory cytokine involved in the regulation of neutrophil survival/activation is granulocyte-macrophage colony-stimulating factor (GM-CSF). Although GM-CSF mediates antiapoptotic effects in neutrophils, it does not prevent apoptosis, and the survival effect is both time dependent and limited. Here, we identified the proapoptotic Bcl-2 family member Bim as an important lifespan limiting molecule in neutrophils, particularly under conditions of survival factor exposure. Strikingly, GM-CSF induced Bim expression in both human and mouse neutrophils that was blocked by pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K). Increased Bim expression was also seen in human immature bone marrow neutrophils as well as in blood neutrophils from septic shock patients; both cell populations are known to be exposed to GM-CSF under in vivo conditions. The functional role of Bim was investigated using Bim-deficient mouse neutrophils in the presence and absence of the survival cytokines interleukin (IL)-3 and GM-CSF. Lack of Bim expression resulted in a much higher efficacy of the survival cytokines to block neutrophil apoptosis. Taken together, these data demonstrate a functional role for Bim in the regulation of neutrophil apoptosis and suggest that GM-CSF and other neutrophil hematopoietins initiate a proapoptotic counterregulation that involves upregulation of Bim.
Andina
N
N
Institute of Pharmacology, University of Bern, Bern CH-3010, Switzerland.
Conus
S
S
Schneider
E M
EM
Fey
M F
MF
Simon
H U
HU
D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D002478:Cells, Cultured; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D007377:Interleukin-3 / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009504:Neutrophils / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011994:Recombinant Proteins; D018805:Sepsis / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D007377:Interleukin-3; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D016179:Granulocyte Colony-Stimulating Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases