Activation of both nuclear factor of activated T cells and inhibitor of nuclear factor-kappa B kinase beta-subunit-/nuclear factor-kappa B is critical for cyclooxygenase-2 induction by benzo[a]pyrene in human bronchial epithelial cells.
The carcinogenic effect of benzo[a]pyrene (B[a]P), presenting mainly in cigarette smoke and air pollution, has been well demonstrated both in vitro and in vivo. However, it is still not well understood how B[a]P facilitates pulmonary carcinogenesis. To explore this, we investigated the effect of B[a]P on the induction of cyclooxygenase-2 (COX-2), a critical enzyme implicated in inflammation and cancer development, as well as upstream signaling pathways leading to its expression in human bronchial epithelial cells (Beas-2B). We found that exposure of Beas-2B to B[a]P caused significant COX-2 induction at both the transcriptional and protein levels. B[a]P also switched on the nuclear factor of activated T cells (NFAT) and nuclear factor kappaB (NF-kappaB) signaling pathways. B[a]P-induced COX-2 expression was significantly blocked by inhibition of the NFAT pathway, and impairment of the NF-kappaB signaling pathway by ectopic expression of an inhibitor of nuclear factor-kappaB kinase beta-subunit (IKKbeta) kinase inactive mutant (IKKbeta-KM) also dramatically inhibited COX-2 induction. The IKKbeta/NF-kappaB-dependent COX-2 induction was further confirmed in mouse embryonic fibroblasts with IKKbeta deficiency (IKKbeta(-/-)) and in those that expressed reconstituted IKKbeta. However, activation of the NFAT and NF-kappaB signaling pathways by B[a]P were independent of each other, as blocking one signaling pathway didn't interrupt the activation of the other one. Mutation of either NFAT or NF-kappaB binding sites significantly blocked COX-2 promoter induction by B[a]P. Taken together, these data indicate that exposure of Beas-2B to B[a]P can upregulate COX-2 expression by increasing its transcription, which requires activation of both the NFAT and NF-kappaB signaling pathways.
Ding
Jin
J
Nelson Institute of Environmental Medicine, New York University School of Medicine, 57 Old Forge Road, Tuxedo, NY 10987, USA.
Wu
Kangjian
K
Zhang
Dongyun
D
Luo
Wenjing
W
Li
Jingxia
J
Ouyang
Weiming
W
Song
Lun
L
Huang
Chuanshu
C
D000595:Amino Acid Sequence; D001564:Benzo(a)pyrene / Q000494:pharmacology*; D001980:Bronchi / Q000166:cytology*; D002461:Cell Line, Transformed; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism* / Q000502:physiology; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism* / Q000502:physiology; D050778:NFATC Transcription Factors / Q000378:metabolism* / Q000502:physiology; D021122:Protein Subunits / Q000378:metabolism / Q000502:physiology; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D016328:NF-kappa B; D050778:NFATC Transcription Factors; D021122:Protein Subunits; D001564:Benzo(a)pyrene; D051546:Cyclooxygenase 2; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse