5-Fluorouracil suppression of NF-KappaB is mediated by the inhibition of IKappab kinase activity in human salivary gland cancer cells.
We have recently shown that 5-Fluorouracil (5-FU) suppresses the transcription factor NF-kappaB in human salivary gland cancer cells (cl-1) by mediating upregulation of IkappaB-alpha expression. However, the precise mechanism involved in this action has not yet been elucidated. IkappaB kinases (IKK-alpha and IKK-beta) are the key components of the IKK complex that mediates activation of NF-kappaB in response to external stimuli such as cytokines. In addition, NF-kappaB-inducing kinase (NIK) and mitogen-activated protein kinase kinase kinase 1 (MEKK-1), both of which are the upstream kinases for the IKKs, interact with and activate the IKKs. Thus, we investigated the molecular mechanisms involved in the suppression of NF-kappaB by 5-FU. Although 5-FU did not affect the expression levels of IKKs, NIK, or MEKK-1, IKK activity in cl-1 cells was suppressed at both 6 h and 12 h after treatment with 2 microgram/ml 5-FU. Moreover, when cells were treated with various concentrations of 5-FU for 12 h, the concentration of 2 microgram/ml efficiently inhibited the IKK activity as compared to 1, 5, or 10 microgram/ml. The expression of Fas-associated death domain-like interleukin 1-converting enzyme-inhibitory protein (FLIP), which acts as an inhibitor of an initiator caspase (caspase-8), was down-regulated by 5-FU treatment in cl-1 cells. Apoptosis, as evidenced by cleavage of poly(ADP-ribose) polymerase through the action of an executioner caspase (caspase-3), was also clearly observed. Thus, these results suggest that 5-FU induction of apoptosis in cl-1 cells may be mediated by suppression of NF-kappaB via inhibition of IKK activity.
Second Department of Oral and Maxillofacial Surgery, Tokushima University School of Dentistry, Tokushima, Japan. azumasa@dent.tokushima-u.ac.jp
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Azuma
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Yamashita
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Aota
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Tamatani
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Sato
D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D006868:Hydrolysis; D051550:I-kappa B Kinase; D048728:MAP Kinase Kinase Kinase 1; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012468:Salivary Gland Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D000097782:NF-kappaB-Inducing Kinase
D005472:Fluorouracil; D051550:I-kappa B Kinase; D048728:MAP Kinase Kinase Kinase 1; D016328:NF-kappa B; D011065:Poly(ADP-ribose) Polymerases; D017346:Protein Serine-Threonine Kinases; D000097782:NF-kappaB-Inducing Kinase; C496559:CHUK protein, human; C496560:IKBKB protein, human; C496565:IKBKE protein, human; C482576:MAP3K1 protein, human