E2F proteins are posttranslationally modified concomitantly with a reduction in nuclear binding activity in cells infected with herpes simplex virus 1.
The transition from G(1) to S phase in the cell cycle requires sequential activation of cyclin-dependent kinase 4 (cdk4) and cdk2, which phosphorylate the retinoblastoma protein, causing the release of E2F. Free E2F upregulates the transcription of genes involved in S phase and cell cycle progression. Recent studies from this and other laboratories have shown that herpes simplex virus 1 stabilizes cyclin D3 early in infection and that early events in viral replication are sensitive to inhibitors of some cdks. On the other hand cdk2 is not activated. Here we report studies on the status of members of E2F family in cycling HEp-2 and HeLa cells and quiescent serum-starved, contact-inhibited human lung fibroblasts. The results show that (i) at 8 h postinfection or thereafter, E2F-1 and E2F-5 were posttranslationally modified and/or translocated from nucleus to the cytoplasm, (ii) E2F-4 was hyperphophorylated, and (iii) overall, E2F binding to cognate DNA sites was decreased at late times after infection. These results concurrent with those cited above indicate that late in infection activation of S-phase genes is blocked both by posttranslational modification and translocation of members of E2F family to inactive compartments and by the absence of active cdk2. The observation that E2F were also posttranslationally modified in quiescent human lung fibroblasts that were not in S phase at the time of infection suggests that specific viral gene products are responsible for modification of the members of E2F family and raises the possibility that in infected cells, activation of the S phase gene is an early event in viral infection and is then shut off at late times. This is consistent with the timing of stabilization of cyclin D3 and the events blocked by inhibitors of cdks.
The Marjorie B. Kovler Viral Oncology Laboratories, The University of Chicago, Chicago, Illinois 60637, USA.
S J
SJ
Advani
R R
RR
Weichselbaum
B
B
Roizman
D000469:Alkaline Phosphatase / Q000494:pharmacology; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050704:E2F4 Transcription Factor; D050700:E2F5 Transcription Factor; D005347:Fibroblasts / Q000821:virology; D006367:HeLa Cells; D018259:Herpesvirus 1, Human / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D010766:Phosphorylation; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050703:E2F2 Transcription Factor; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D050700:E2F5 Transcription Factor; C092558:E2F5 protein, human; D020033:Protein Isoforms; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D018844:Cyclin-Dependent Kinases; D000469:Alkaline Phosphatase