NF-kappaB protects rat ARL-6 hepatocellular carcinoma cells against hydrogen peroxide-induced apoptosis.
OBJECTIVE
Refractoriness of some tumours to apoptosis has been related to over-expression of NF-kappaB, while NF-kappaB inhibition can promote apoptosis in several cell types. We compared NF-kappaB activation profiles between normal rat hepatocytes and ARL-6 rat hepatocellular carcinoma (HCC) cells exposed to hydrogen peroxide (H2O2), and examined whether NF-kappaB activation could explain the observed resistance to apoptosis of ARL-6 cells. We then infected ARL-6 cells with recombinant adenovirus containing mutant (non-degradable) IkBa (Adv-mIkappaBalpha), and examined whether this rendered ARL-6 cells more sensitive to oxidative stress-induced apoptosis.


METHODS
Cultured primary rat hepatocytes and ARL-6 cells were treated with graded doses of H2O2. To block NF-kappaB, ARL-6 cells were incubated with Adv-mIkappaBalpha for 24 h. Cytotoxicity, NF-kappaB activation, cell proliferation, and apoptosis were determined.


RESULTS
H2O2 induced more apoptosis in primary hepatocytes than ARL-6 cells, and the relative resistance of ARL-6 cells to H2O2-induced apoptosis was associated with more pronounced NF-kappaB activity. In ARL-6 cells, nuclear translocation of NF-kappaB took place within 2 h of administering H2O2 and remained prominent at 36 h. Adv-mIkappaBalpha sensitized ARL-6 cells to H2O2-induced apoptosis, but cell proliferation was minimally suppressed.


CONCLUSIONS
Compared with normal hepatocytes, ARL-6 cells are refractory to apoptosis after exposure to H2O2, and this is associated with NF-kappaB activation. Conversely, NF-kappaB inhibition sensitises ARL-6 cells to H2O2-induced apoptosis. Sustained NF-kappaB activation in these HCC cells may protect them against apoptosis produced by oxidative stress.
Qiao
Liang
L
Storr Liver Unit, Westmead Millennium Institute, University of Sydney at Westmead Hospital, Westmead, NSW214-5, Australia.
Yu
Jun
J
Dent
Paul
P
Farrell
Geoffrey
G
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D019610:Cytoprotection; D004305:Dose-Response Relationship, Drug; D022781:Hepatocytes / Q000187:drug effects* / Q000648:ultrastructure; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000473:pathology*; D008297:Male; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D016328:NF-kappa B; D016877:Oxidants; D006861:Hydrogen Peroxide