Macrophages require constitutive NF-kappaB activation to maintain A1 expression and mitochondrial homeostasis.
NF-kappaB is a critical mediator of macrophage inflammatory responses, but its role in regulating macrophage survival has yet to be elucidated. Here, we demonstrate that constitutive NF-kappaB activation is essential for macrophage survival. Blocking the constitutive activation of NF-kappaB with pyrrolidine dithiocarbamate or expression of IkappaBalpha induced apoptosis in macrophagelike RAW 264.7 cells and primary human macrophages. This apoptosis was independent of additional death-inducing stimuli, including Fas ligation. Suppression of NF-kappaB activation induced a time-dependent loss of mitochondrial transmembrane potential (DeltaPsi(m)) and DNA fragmentation. Examination of initiator caspases revealed the cleavage of caspase 9 but not caspase 8 or the effector caspase 3. Addition of a general caspase inhibitor, z-VAD. fmk, or a specific caspase 9 inhibitor reduced DNA fragmentation but had no effect on DeltaPsi(m) collapse, indicating this event was caspase independent. To determine the pathway leading to mitochondrial dysfunction, analysis of Bcl-2 family members established that only A1 mRNA levels were reduced prior to DeltaPsi(m) loss and that ectopic expression of A1 protected against cell death following inactivation of NF-kappaB. These data suggest that inhibition of NF-kappaB in macrophages initiates caspase 3-independent apoptosis through reduced A1 expression and mitochondrial dysfunction. Thus, constitutive NF-kappaB activation preserves macrophage viability by maintaining A1 expression and mitochondrial homeostasis.
Pagliari
L J
LJ
Division of Rheumatology, Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60611, USA.
Perlman
H
H
Liu
H
H
Pope
R M
RM
D017209:Apoptosis; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004789:Enzyme Activation; D018398:Homeodomain Proteins; D006706:Homeostasis; D006801:Humans; D020672:I-kappa B Proteins; D007425:Intracellular Membranes / Q000502:physiology; D008264:Macrophages / Q000502:physiology*; D015778:Minor Histocompatibility Antigens; D008928:Mitochondria / Q000502:physiology*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D018892:Proton-Motive Force; D011759:Pyrrolidines / Q000494:pharmacology; D051818:Replication Protein C; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013859:Thiocarbamates / Q000494:pharmacology
C096816:BCL2-related protein A1; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D020672:I-kappa B Proteins; C096063:MATA1 protein, S cerevisiae; D015778:Minor Histocompatibility Antigens; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D011759:Pyrrolidines; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D013859:Thiocarbamates; D000072000:NF-KappaB Inhibitor alpha; C020972:pyrrolidine dithiocarbamic acid; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D051818:Replication Protein C