Augmenter of liver regeneration causes different kinetics of ERK1/2 and Akt/PKB phosphorylation than EGF and induces hepatocyte proliferation in an EGF receptor independent and liver specific manner.
OBJECTIVE
Augmenter of liver regeneration (ALR) is a potent growth factor which supports liver regeneration in experimental animals. The aim of this study was to compare proliferation as well as the kinetics of ERK1/2 and Akt/PKB phosphorylation by recombinant human ALR (rhALR) and EGF in human hepatocytes and extrahepatic cells.


METHODS
Kinetics of ERK1/2 and Akt/PKB phosphorylation were determined in primary human hepatocytes (phh) after stimulation with rhALR and EGF. Induction of proliferation was analyzed in phh and several cell lines of hepatic and extrahepatic origin by the MTT and [(3)H]-thymidine assay.


RESULTS
The kinetics of ERK phosphorylation showed clear differences, whereby rhALR caused a transient and EGF a permanent increase during the observation period of 60 min. For both, Akt and ERK phosphorylation, EGF caused a faster effect with maximal levels observed already after 2 min, whereas rhALR caused maximal phosphorylation between 10 and 15 min. Using the EGF receptor inhibitor AG1478 we provide evidence of an EGF receptor independent induction of proliferation by rhALR. Furthermore, rhALR induced proliferation only in phh and the human liver derived cell lines HepG2 and Chang. In contrast, EGF enhanced proliferation in all analyzed cell types including cell lines of colon, bronchial, pancreatic and gastric origin (SW480, BC1, L36PL and GC1).


CONCLUSIONS
rhALR and EGF induce different kinetics of ERK and Akt phosphorylation in human hepatocytes. The mitogenic effect of rhALR is liver specific and seems to be at least partially independent from EGF receptor mediated signaling.
Department of Surgery, Ludwig-Maximilians-University of Munich Hospital Grosshadern, Munich, Germany.
Maren
M
Ilowski
Christine
C
Putz
Thomas S
TS
Weiss
Stephan
S
Brand
Karl-Walter
KW
Jauch
Jan G
JG
Hengstler
Wolfgang Erwin
WE
Thasler
D002460:Cell Line; D049109:Cell Proliferation; D003579:Cytochrome Reductases / Q000494:pharmacology*; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000819:agonists / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008115:Liver Regeneration / Q000187:drug effects*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D050862:Oxidoreductases Acting on Sulfur Group Donors; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology*
D011994:Recombinant Proteins; D004815:Epidermal Growth Factor; D003579:Cytochrome Reductases; C500897:GFER protein, human; D050862:Oxidoreductases Acting on Sulfur Group Donors; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3