Induction of anti-proliferative mechanisms in hepatitis B virus producing cells.
OBJECTIVE
Hepatitis B virus (HBV) preferentially replicates in quiescent cells. It was analyzed whether HBV affects cell cycle control.


METHODS
The amount of EGF-receptor (EGFR) and the binding capacity for 125I-EGF was determined. Expression of mdm2 and p21 and relevance of p53 for it were analyzed by reporter gene assays and western blotting. Cyclin A/E associated cdk2 activities were determined by immunocomplex assays. Cell proliferation was quantified by measurement of BrdU incorporation.


RESULTS
In HBV producing cells a significant reduction of EGFR expression, diminished 125I-EGF-binding capacity and insensitivity to EGF-stimulation were observed as compared to the control. Moreover, c-Raf-1-dependent induction of mdm2-P2 and p21cip1/waf1-promoter and elevated amounts of the respective proteins were observed in HBV producing cells. Whereas activation of mdm2-P2-promoter requires p53, activation of p21cip1/waf1-promoter is mediated partially by a p53-independent process. Induction of p21cip1/waf1 is reflected by a reduction of cyclin A associated cdk2 activity and an increase of cyclin E associated cdk2 activity. In accordance with this proliferation rate of HBV-producing hepatocytes is reduced as compared to control cells.


CONCLUSIONS
These results describe novel cell-cycle inhibitory functions of HBV that correlate well with the general concept of enhanced HBV replication in quiescent cells.
Friedrich
Beate
B
Robert Koch-Institute, D-13353 Berlin, Germany.
Wollersheim
Madlen
M
Brandenburg
Boerries
B
Foerste
Ramona
R
Will
Hans
H
Hildt
Eberhard
E
D006528:Carcinoma, Hepatocellular; D002453:Cell Cycle / Q000502:physiology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D019925:Cyclin A / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D017930:Genes, Reporter; D006515:Hepatitis B virus / Q000502:physiology*; D006801:Humans; D008113:Liver Neoplasms; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014779:Virus Replication / Q000502:physiology*
D019925:Cyclin A; D019927:Cyclin E; D004815:Epidermal Growth Factor; D066246:ErbB Receptors