C-myc is required for the G0/G1-S transition of primary hepatocytes stimulated with a deleted form of hepatocyte growth factor.
Primary rat hepatocytes stimulated in vitro with the addition of a deleted form of hepatocyte growth factor (dHGF) enter the S-phase 48 h after addition of the growth factor. The c-myc gene is believed to play a role in a variety of cellular stages, such as proliferation, differentiation and cell death. In primary hepatocytes c-myc was expressed constitutively at both mRNA and protein levels, independently of the growth conditions. dHGF induced significant c-myc expression at times correlated with the long-lasting pre-S phase, and no induction was observed at the G0/G1 traverse compared with the unstimulated hepatocytes. An antisense construct coding for all three exons of c-myc was imported into hepatocytes by using the transferrin receptor-mediated endocytosis methodology (transferrinfection). Expression of the antisense construct inhibited the biosynthesis of the c-Myc protein, however it did not interfere with the expression of c-met, encoding the receptor for HGF/dHGF. Continuous expression of the antisense construct inhibited entry of the hepatocytes into the S-phase. Regulated induction of the antisense c-myc by dexamethasone for up to 6 h in culture, did not interfere with the entry of hepatocytes into the S-phase. c-myc expression was shown to be required between 6 and 12 h in dHGF-stimulated hepatocytes, and inhibition of its expression during this time by the antisense myc construct did not allow these cells to enter the S-phase. Inhibition of c-myc biosynthesis between 24 and 48 h hours slightly affected the DNA synthetic response. It is proposed that the expression of c-Myc protein interferes with the "priming' of hepatocytes to become responsive to growth-factor stimuli, or in the absence of such stimuli it interferes with the maintenance of a non-proliferating phenotype and subsequent in vitro de-differentiation.
Skouteris
G G
GG
Department of Applied Tumour Virology, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Schröder
C H
CH
D000818:Animals; D002453:Cell Cycle; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D016373:DNA, Antisense / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D005091:Exons; D016193:G1 Phase; D016259:Genes, myc; D017228:Hepatocyte Growth Factor / Q000096:biosynthesis / Q000494:pharmacology*; D008099:Liver / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D010957:Plasmids; D019859:Proto-Oncogene Proteins c-met; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000494:pharmacology; D016192:Resting Phase, Cell Cycle; D016196:S Phase; D017384:Sequence Deletion; D014162:Transfection
D016373:DNA, Antisense; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D017228:Hepatocyte Growth Factor; D003907:Dexamethasone; D004247:DNA; D019859:Proto-Oncogene Proteins c-met; D020794:Receptor Protein-Tyrosine Kinases