Silica induces nuclear factor-kappa B activation through tyrosine phosphorylation of I kappa B-alpha in RAW264.7 macrophages.
It was previously reported that protein tyrosine kinase (PTK) but not protein kinase C or A plays an important role in silica-induced activation of NF-kappa B in macrophages. The question is raised whether PTK stimulation and NF-kappa B activation in silica-stimulated macrophages are directly connected through tyrosine phosphorylation of I kappa B-alpha. Results indicate that stimulation of macrophages with silica led to NF-kappaB activation through tyrosine phosphorylation without serine phosphorylation. Specific inhibitors of protein tyrosine kinase, such as genistein and tyrophostin AG126, prevented tyrosine phosphorylation of I kappa B-alpha in response to silica. I kappa B-alpha protein levels remained relatively unchanged for up to 60 min after silica stimulation. Moreover, inhibition of proteasome proteolytic activity did not affect NF-kappa B activation by silica. Antioxidants, such as superoxide dismutase (SOD), N-acetylcysteine (NAC), and pyrrolidine dithiocarbamate (PDTC), blocked tyrosine phosphorylation of I kappa B-alpha induced by silica, suggesting reactive oxygen species (ROS) may be important regulatory molecules in NF-kappa B activation through tyrosine phosphorylation of I kappa B-alpha. The results suggest that tyrosine phosphorylation of I kappa B-alpha represents a proteasome proteolytic activity-independent mechanism for NF-kappa B activation that directly couples NF-kappa B to cellular tyrosine kinase in silica-stimulated macrophages. This proposed mechanism of NF-kappa B activation induced by silica could be used as a target for development of antiinflammatory and antifibrosis drugs.
Kang
J L
JL
Department of Physiology, College of Medicine, Ewha Woman's University, Seoul, #158-056, Korea. jihee@mm.ewha.ac.kr
Pack
I S
IS
Hong
S M
SM
Lee
H S
HS
Castranova
V
V
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D020672:I-kappa B Proteins / Q000378:metabolism*; D008262:Macrophage Activation / Q000187:drug effects* / Q000502:physiology; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D012822:Silicon Dioxide / Q000633:toxicity*; D013482:Superoxide Dismutase / Q000494:pharmacology; D013859:Thiocarbamates / Q000494:pharmacology; D020032:Tyrphostins / Q000494:pharmacology
D004791:Enzyme Inhibitors; D020672:I-kappa B Proteins; D016328:NF-kappa B; D011759:Pyrrolidines; D017382:Reactive Oxygen Species; D013859:Thiocarbamates; D020032:Tyrphostins; C069028:AG 127; C020972:pyrrolidine dithiocarbamic acid; D012822:Silicon Dioxide; D019833:Genistein; D013482:Superoxide Dismutase; D017027:Protein Tyrosine Phosphatases; D000111:Acetylcysteine