Induction of oxidative stress by okadaic acid is required for activation of transcription factor NF-kappa B.
The widely used phosphatase 1 and 2A inhibitor okadaic acid is one of the many stimuli activating transcription factor NF-kappa B in cultured cells. Phosphorylation of I kappa B-alpha, one of NF-kappa B's inhibitory subunits, is a prerequisite for I kappa B degradation and the subsequent liberation of transcriptionally active NF-kappa B. This observation suggested that the phosphorylation status of I kappa B is influenced by an okadaic acid-sensitive phosphatase. In this study, we provide evidence that the effect of okadaic acid on NF-kappa B activation is indirect and dependent on the production of reactive oxygen intermediates rather than the inhibition of an I kappa B-alpha phosphatase. Okadaic acid was found to be a strong inducer of cellular H2O2 and superoxide production in two distinct cell lines. The structurally unrelated phosphatase inhibitor calyculin A also induced oxidative stress. The delayed onset of reactive oxygen production in response to okadaic acid correlated with the delayed activation of NF-kappa B. Moreover, NF-kappa B induction was optimal at the same okadaic acid concentration that caused optimal H2O2 production. Both reactive oxygen intermediates production and NF-kappa B activation were inhibited by the antioxidant pyrrolidine dithiocarbamate and 8-(diethylamino)octyl-3,4,5-trimethyoxybenzoate, a Ca2+ chelator. Future experiments using phosphatase inhibitors in intact cells must consider that the compounds can act as strong inducers of oxidative stress, which provides one explanation for their tumor-promoting activity.
Schmidt
K N
KN
Institute of Biochemistry, Albert-Ludwigs-University, Freiburg, Germany.
Traenckner
E B
EB
Meier
B
B
Baeuerle
P A
PA
D000975:Antioxidants / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004988:Ethers, Cyclic / Q000008:administration & dosage / Q000494:pharmacology*; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D011759:Pyrrolidines / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D013859:Thiocarbamates / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects
D000975:Antioxidants; D002121:Calcium Channel Blockers; D004988:Ethers, Cyclic; D016328:NF-kappa B; D011759:Pyrrolidines; D017382:Reactive Oxygen Species; D013859:Thiocarbamates; D019319:Okadaic Acid; C020972:pyrrolidine dithiocarbamic acid; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D006861:Hydrogen Peroxide; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1