Sensitization by interleukin-6 of rat hepatocytes to tumor necrosis factor alpha-induced apoptosis.
OBJECTIVE
Tumor necrosis factor (TNF) elicits hepatocyte apoptosis in toxic liver injury and is also central in hepatocyte proliferation after partial hepatectomy. In both circumstances interleukin (IL)-6 levels are also elevated. In mouse liver IL-6 attenuated Fas receptor-mediated apoptosis indicating its interference with pro-apoptotic signal chains. It was, therefore, the aim to examine the modulation by IL-6 of TNFalpha-induced apoptosis in rat hepatocytes.


METHODS
Primary rat hepatocytes were treated with IL-6 prior to induction of apoptosis with TNFalpha/actinomycin D or anti-Fas antibody M-20. Apoptosis was detected by determination of caspase-3 activation and bisbenzimide staining of condensed nuclei. Expression of TNFalpha receptors was analyzed by semi-quantitative polymerase chain reaction and ligand binding studies with [125I]-TNFalpha.


RESULTS
IL-6 treatment doubled TNFalpha/actinomycin D-induced caspase-3 activity and significantly enhanced chromatin condensation. By contrast IL-6 inhibited Fas-induced increase in caspase-3 activity by 45% and significantly reduced chromatin condensation. IL-6 increased the mRNA level of TNF-R1 1.35-fold and augmented cell surface binding of [125I]-TNFalpha 3-fold. The latter and TNFalpha-mediated caspase activation was attenuated by prostaglandin E(2).


CONCLUSIONS
IL-6 - in contrast to its anti-apoptotic modulation of the Fas-induced pathway - exerted a pro-apoptotic effect on the TNFalpha/actinomycin D-induced apoptosis by increasing the number of TNF-R on hepatocytes.
Böer
Ulrike
U
Institut für Ernährungswissenschaft, Universität Potsdam, Abt. Biochemie der Ernährung, Arthur-Scheunert-Allee 114-116, D-14558, Bergholz-Rehbrücke, Germany.
Fennekohl
Alexandra
A
Püschel
Gerhard P
GP
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002843:Chromatin / Q000187:drug effects / Q000502:physiology; D003609:Dactinomycin / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D004357:Drug Synergism; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D015850:Interleukin-6 / Q000494:pharmacology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D002843:Chromatin; D015850:Interleukin-6; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D015232:Dinoprostone