Different mechanisms involved in apoptosis following exposure to benzo[a]pyrene in F258 and Hepa1c1c7 cells.
The present study compares and elucidates possible mechanisms why B[a]P induces different cell signals and triggers apparently different apoptotic pathways in two rather similar cell lines (hepatic epithelial cells of rodents). The rate and maximal capacity of metabolic activation, as measured by the formation of B[a]P-tetrols and B[a]P-DNA adducts, was much higher in mouse hepatoma Hepa1c1c7 cells than in rat liver epithelial F258 cells due to a higher induced level of cyp1a1. B[a]P increased intracellular pH in both cell lines, but this change modulated the apoptotic process only in F258 cells. In Hepa1c1c7 cells reactive oxygen species (ROS) production appeared to be a consequence of toxicity, unlike F258 cells in which it was an initial event. The increased mitochondrial membrane potential found in F258 cells was not observed in Hepa1c1c7 cells. Surprisingly, F258 cells cultured at low cell density were somewhat more sensitive to low (50nM) B[a]P concentrations than Hepa1c1c7 cells. This could be explained partly by metabolic differences at low B[a]P concentrations. In contrast to the Hepa1c1c7 model, no activation of cell survival signals including p-Akt, p-ERK1/2 and no clear inactivation of pro-apoptotic Bad was observed in the F258 model following exposure to B[a]P. Another important difference between the two cell lines was related to the role of Bax and cytochrome c. In Hepa1c1c7 cells, B[a]P exposure resulted in a "classical" translocation of Bax to the mitochondria and release of cytochrome c, whereas in F258 cells no intracellular translocation of these two proteins was seen. These results suggest that the rate of metabolism of B[a]P and type of reactive metabolites formed influence the resulting balance of pro-apoptotic and anti-apoptotic cell signaling, and hence the mechanisms involved in cell death and the chances of more permanent genetic damage.
Holme
Jørn A
JA
Division of Environmental Medicine, Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, N-0403 Oslo, Norway. jorn.holme@fhi.no
Gorria
Morgane
M
Arlt
Volker M
VM
Ovrebø
Steinar
S
Solhaug
Anita
A
Tekpli
Xavier
X
Landvik
Nina E
NE
Huc
Laurence
L
Fardel
Olivier
O
Lagadic-Gossmann
Dominique
D
D000818:Animals; D017209:Apoptosis; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D001564:Benzo(a)pyrene / Q000633:toxicity*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D065633:Cytochrome P-450 CYP1B1; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D001564:Benzo(a)pyrene; D001189:Aryl Hydrocarbon Hydroxylases; C585498:Cyp1b1 protein, mouse; C585499:Cyp1b1 protein, rat; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases