NF-kappaB activation by camptothecin. A linkage between nuclear DNA damage and cytoplasmic signaling events.
Activation of the transcription factor NF-kappaB by extracellular signals involves its release from the inhibitor protein IkappaBalpha in the cytoplasm and subsequent nuclear translocation. NF-kappaB can also be activated by the anticancer agent camptothecin (CPT), which inhibits DNA topoisomerase (Topo) I activity and causes DNA double-strand breaks during DNA replication to induce S phase-dependent cytotoxicity. Here we show that CPT activates NF-kappaB by a mechanism that is dependent on initial nuclear DNA damage followed by cytoplasmic signaling events. NF-kappaB activation by CPT is dramatically diminished in cytoplasts and in CEM/C2 cells expressing a mutant Topo I protein that fails to bind CPT. This response is intensified in S phase cell populations and is prevented by the DNA polymerase inhibitor aphidicolin. In addition, CPT activation of NF-kappaB involves degradation of cytoplasmic IkappaBalpha by the ubiquitin-proteasome pathway in a manner that depends on the IkappaB kinase complex. Finally, inhibition of NF-kappaB activation augments CPT-induced apoptosis. These findings elucidate the progression of signaling events that initiates in the nucleus with CPT-Topo I interaction and continues in the cytoplasm resulting in degradation of IkappaBalpha and nuclear translocation of NF-kappaB to attenuate the apoptotic response.
Huang
T T
TT
Program in Molecular and Cellular Pharmacology, Madison, Wisconsin 53792, USA.
Wuerzberger-Davis
S M
SM
Seufzer
B J
BJ
Shumway
S D
SD
Kurama
T
T
Boothman
D A
DA
Miyamoto
S
S
D017209:Apoptosis; D001483:Base Sequence; D002166:Camptothecin / Q000494:pharmacology*; D002467:Cell Nucleus / Q000187:drug effects* / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects* / Q000378:metabolism; D004249:DNA Damage; D017931:DNA Primers; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D016196:S Phase / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*; D019772:Topotecan / Q000494:pharmacology; D014452:Ubiquitins / Q000378:metabolism
D017931:DNA Primers; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D014452:Ubiquitins; D000072000:NF-KappaB Inhibitor alpha; D019772:Topotecan; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D002166:Camptothecin