JNK modulates the effect of caspases and NF-kappaB in the TNF-alpha-induced down-regulation of Na+/K+ATPase in HepG2 cells.
An inhibition of the Na(+)/K(+)ATPase was previously shown to accompany and potentiate apoptosis in different experimental models. Since TNF-alpha is known to be a pro and anti-apoptotic cytokine, this work was undertaken to study the effect of TNF-alpha on the Na(+)/K(+)ATPase in HepG2 cells and to determine the signaling pathway involved. Cells were incubated for 1 h with TNF-alpha in presence and absence of PDTC, SP600125 and FK009, respective inhibitors of NF-KB, c-JNK, and caspases. The activity of the pump was assayed by measuring the ouabain-inhibitable release of inorganic phosphate, and changes in its expression were monitored by western blot analysis. TNF-alpha decreased significantly the activity and protein expression of the Na(+)/K(+)ATPase. NF-kappaB and caspases were found to be the main effectors of the cytokine, mediating respectively down-regulation and up-regulation of the pump. Their activity was however modulated at 1 h by c-JNK, which stimulated the caspases and inhibited NF-kappaB, resulting in a net inhibition of the ATPase, and probably favoring the apoptotic pathway.
Kassardjian
Ari
A
Department of Biology, Faculty of Arts & Sciences, American University of Beirut, Beirut, Lebanon.
Kreydiyyeh
Sawsan Ibrahim
SI
D000818:Animals; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*
D004791:Enzyme Inhibitors; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D048031:JNK Mitogen-Activated Protein Kinases; D020169:Caspases; D000254:Sodium-Potassium-Exchanging ATPase