Multiple division cycles and long-term survival of hepatocytes are distinctly regulated by extracellular signal-regulated kinases ERK1 and ERK2.
We investigated the specific role of the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 1 (ERK1)/ERK2 pathway in the regulation of multiple cell cycles and long-term survival of normal hepatocytes. An early and sustained epidermal growth factor (EGF)-dependent MAPK activation greatly improved the potential of cell proliferation. In this condition, almost 100% of the hepatocytes proliferated, and targeting ERK1 or ERK2 via RNA interference revealed the specific involvement of ERK2 in this regulation. However, once their first cell cycle was performed, hepatocytes failed to undergo a second round of replication and stayed blocked in G1 phase. We demonstrated that sustained EGF-dependent activation of the MAPK/ERK kinase (MEK)/ERK pathway was involved in this blockage as specific transient inhibition of the cascade repotentiated hepatocytes to perform a new wave of replication and multiple cell cycles. We identified this mechanism by showing that this blockage was in part supported by ERK2-dependent p21 expression. Moreover, continuous MEK inhibition was associated with a lower apoptotic engagement, leading to an improvement of survival up to 3 weeks. Using RNA interference and ERK1 knockout mice, we extended these results by showing that this improved survival was due to the specific inhibition of ERK1 expression/phosphorylation and did not involve ERK2.


CONCLUSIONS
Our results emphasize that transient MAPK inhibition allows multiple cell cycles in primary cultures of hepatocytes and that ERK2 has a key role in the regulation of S phase entry. Moreover, we revealed a major and distinct role of ERK1 in the regulation of hepatocyte survival. Taken together, our results represent an important advance in understanding long-term survival and cell cycle regulation of hepatocytes.
Frémin
Christophe
C
INSERM U522, UPRES SeRAIC, IFR 140 Université de Rennes, Rennes, France.
Bessard
Anne
A
Ezan
Frédéric
F
Gailhouste
Luc
L
Régeard
Morgane
M
Le Seyec
Jacques
J
Gilot
David
D
Pagès
Gilles
G
Pouysségur
Jacques
J
Langouët
Sophie
S
Baffet
Georges
G
D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D017207:Rats, Sprague-Dawley
D050759:Cyclin-Dependent Kinase Inhibitor p21; D004815:Epidermal Growth Factor; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases