title: Granulocyte macrophage colony-stimulating factor signaling and proteasome inhibition delay neutrophil apoptosis by increasing the stability of Mcl-1.
abstract: Human neutrophils normally have a very short half-life and die by apoptosis. Cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) can delay this apoptosis via increases in the cellular levels of Mcl-1, an anti-apoptotic protein of the Bcl-2 family with a rapid turnover rate. Here we have shown that inhibition of the proteasome (a) decreases the rate of Mcl-1 turnover within neutrophils and (b) significantly delays apoptosis. This led us to determine whether GM-CSF could enhance neutrophil survival by altering the rate of Mcl-1 turnover. Addition of GM-CSF to neutrophils enhanced Mcl-1 stability and delayed apoptosis by signaling pathways requiring PI3K/Akt and p44/42 Erk/Mek, because inhibitors of these pathways completely abrogated the GM-CSF-mediated effect on both Mcl-1 stability and apoptosis delay. Conversely, induction of Mcl-1 hyperphosphorylation by the phosphatase inhibitor, okadaic acid, significantly accelerated both Mcl-1 turnover and apoptosis. Neither the calpain inhibitor, carbobenzoxy-valinyl-phenylalaninal, nor the pan caspase inhibitor, benzyloxycarbonyl-VAD-fluoromethylketone, had any effect on Mcl-1 stability under these conditions. These observations indicate that profound changes in the rate of neutrophil apoptosis following cytokine signaling occur via dynamic changes in the rate of Mcl-1 turnover via the proteasome.
authors.affiliation: School of Biological Sciences, Biosciences Building and Department of Medicine, University of Liverpool, Liverpool L69 7ZB, United Kingdom.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Derouet
authors.forename: Luke
authors.initials: L
authors.lastname: Thomas
authors.forename: Andrew
authors.initials: A
authors.lastname: Cross
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Moots
authors.forename: Steven W
authors.initials: SW
authors.lastname: Edwards
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002154:Calpain / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism*; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D015398:Signal Transduction
chemical_list: D002154:Calpain; D020169:Caspases; D003513:Cycloheximide; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D007976:Leupeptins; D020928:Mitogen-Activated Protein Kinases; D009097:Multienzyme Complexes; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010744:Phosphoric Monoester Hydrolases; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; C494918:AKT1 protein, human; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde