Activation of NF-kappa B by phosphatase inhibitors involves the phosphorylation of I kappa B alpha at phosphatase 2A-sensitive sites.
Activation of NF-kappa B by various cellular stimuli involves the phosphorylation and subsequent degradation of its inhibitor, I kappa B alpha, although the underlying mechanism remains unclear. In the present study, the role of serine/threonine phosphatases in the regulation of I kappa B alpha phosphorylation was investigated. Our studies demonstrate that incubation of human T cells with low concentrations (approximately 1-5 nM) of calyculin A or okadaic acid, potent inhibitors of protein phosphatase type 1 (PP-1) and type 2A (PP-2A), induces the phosphorylation of I kappa B alpha even in the absence of any cellular stimulus. This action of the phosphatase inhibitors, which is associated with the activation of the RelA.p50 NF-kappa B heterodimer, is not affected by agents that block the induction of I kappa B alpha phosphorylation by tumor necrosis factor alpha (TNF-alpha). Furthermore, the phosphorylated I kappa B alpha from calyculin A-treated cells, but not that from TNF-alpha-stimulated cells, is sensitive to PP-2A in vitro, suggesting the existence of fundamental differences in the phosphorylation of I kappa B alpha induced by the two different NF-kappa B inducers. However, induction of I kappa B alpha phosphorylation by both TNF-alpha and the phosphatase inhibitors is associated with the subsequent degradation of I kappa B alpha. We further demonstrate that TNF-alpha- and calyculin A-induced I kappa B alpha degradation exhibits similar but not identical sensitivities to a proteasome inhibitor. Together, these results suggest that phosphorylation of I kappa B alpha, mediated through both the TNF-alpha-inducible and the PP-2A-opposing kinases, may serve to target I kappa B alpha for proteasome-mediated degradation.
Sun
S C
SC
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey Medical Center 17033, USA.
Maggirwar
S B
SB
Harhaj
E
E
D003546:Cysteine Endopeptidases / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D006801:Humans; D020672:I-kappa B Proteins; D007976:Leupeptins / Q000494:pharmacology; D008387:Marine Toxins; D009097:Multienzyme Complexes / Q000187:drug effects; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D019319:Okadaic Acid; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D054648:Protein Phosphatase 2; D011499:Protein Processing, Post-Translational; D015398:Signal Transduction; D013601:T-Lymphocytes; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D020672:I-kappa B Proteins; D007976:Leupeptins; D008387:Marine Toxins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D010080:Oxazoles; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D019319:Okadaic Acid; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde