Induction of DNA synthesis in primary mouse hepatocytes is associated with nuclear pro-transforming growth factor alpha and erbb-1 and is independent of c-jun.
For growth stimulation of liver cells by hepatocyte growth factor (HGF) or transforming growth factor alpha (TGFalpha) via receptor tyrosine kinases, c-fos/c-jun has been considered a point of intersection for cross-talk between the different signal transduction pathways. Recent evidence strongly implicates translocation of pro-TGFalpha into the nucleus as an important step preceding the initiation of hepatic DNA synthesis. We asked whether an active c-jun is required for the nuclear translocation of pro-TGFalpha and its stimulatory effect on DNA synthesis. For this purpose we used mice with c-jun inactivated post partum in hepatocytes by the Cre-loxP recombination system (c-jun(Deltaliver)). Nuclear fractions from control and c-jun(Deltaliver) mouse livers contained TGFalpha as pro-form of 17 kDa and the epidermal growth factor receptor (erbb-1) with molecular weights of 170 and 150 kDa (truncated form). Hepatocytes were isolated by collagenase perfusion and cultivated. A lack of c-jun did not alter the apoptotic activity but significantly suppressed DNA synthesis in the cultured hepatocytes. In control and c-jun(Deltaliver) cells DNA synthesis was almost always associated with nuclear presence of pro-TGFalpha. 76.5 +/- 6.8% of hepatocytes with pro-TGFalpha positive nuclei and only 4.52 +/- 1.31% of hepatocytes with negative nuclei exhibited DNA replication. About 85% of the pro-TGFalpha positive nuclei also contained erbb-1. Treatment of cultures with mature TGFalpha or HGF elevated the frequency of pro-TGFalpha positive nuclei replicating DNA; HGF and TGFalpha-induced nuclear pro-TGFalpha and DNA synthesis significantly more in c-jun(Deltaliver) than in control hepatocytes. These results suggest that (i) a lack of c-jun suppresses basal rates of DNA replication in hepatocytes; (ii) c-jun deficient hepatocytes show a pronounced growth response towards HGF or TGFalpha; (iii) nuclear translocation of pro-TGFalpha together with erbb-1 and its association with DNA synthesis are independent of c-jun.
Schausberger
Elisabeth
E
Institut für Krebsforschung, University of Vienna, Borschkegasse 8a, Austria.
Eferl
Robert
R
Parzefall
Wolfram
W
Chabicovsky
Monica
M
Breit
Paul
P
Wagner
Erwin F
EF
Schulte-Hermann
Rolf
R
Grasl-Kraupp
Bettina
B
Chabikovsky
Monica
M
D000818:Animals; D015139:Blotting, Southern; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004261:DNA Replication; D015180:Electrophoresis, Gel, Two-Dimensional; D066246:ErbB Receptors / Q000378:metabolism*; D017228:Hepatocyte Growth Factor / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D015151:Immunoblotting; D019426:Integrases; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011498:Protein Precursors / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D011995:Recombination, Genetic; D016211:Transforming Growth Factor alpha / Q000378:metabolism* / Q000494:pharmacology; D014764:Viral Proteins
D011498:Protein Precursors; D016755:Proto-Oncogene Proteins c-jun; D016211:Transforming Growth Factor alpha; D014764:Viral Proteins; C052268:protransforming growth factor alpha; D017228:Hepatocyte Growth Factor; D004247:DNA; D066246:ErbB Receptors; C045073:Cre recombinase; D019426:Integrases