Poly(ADP-ribose) polymerase upregulates E2F-1 promoter activity and DNA pol alpha expression during early S phase.
E2F-1, a transcription factor implicated in the activation of genes required for S phase such as DNA pol alpha, is regulated by interactions with Rb and by cell-cycle dependent alterations in E2F-1 abundance. We have shown that depletion of poly(ADP-ribose) polymerase (PARP) by antisense RNA expression downregulates pol alpha and E2F-1 expression during early S phase. To examine the role of PARP in the regulation of pol alpha and E2F-1 gene expression, we utilized immortalized mouse fibroblasts derived from wild-type and PARP knockout (PARP-/-) mice as well as PARP-/- cells stably transfected with PARP cDNA [PARP-/-(+PARP)]. After release from serum deprivation, wild-type and PARP-/-(+PARP) cells, but not PARP-/- cells, exhibited a peak of cells in S phase by 16 h and had progressed through the cell cycle by 22 h. Whereas [3H]thymidine incorporation remained negligible in PARP-/- cells, in vivo DNA replication maximized after 18 h in wild-type and PARP-/-(+PARP) cells. To investigate the effect of PARP on E2F-1 promoter activity, a construct containing the E2F-1 gene promoter fused to a luciferase reporter gene was transiently transfected into these cells. E2F-1 promoter activity in control and PARP-/-(+PARP) cells increased eightfold after 9 h, but not in PARP-/- cells. PARP-/- cells did not show the marked induction of E2F-1 expression during early S phase apparent in control and PARP-/-(+PARP) cells. RT - PCR analysis and pol alpha activity assays revealed the presence of pol alpha transcripts and a sixfold increase in activity in both wild-type and PARP-/-(+PARP) cells after 20 h, but not in PARP-/- cells. These results suggest that PARP plays a role in the induction of E2F-1 promoter activity, which then positively regulates both E2F-1 and pol alpha expression, when quiescent cells reenter the cell cycle upon recovery from aphidicolin exposure or removal of serum.
Simbulan-Rosenthal
C M
CM
Department of Biochemistry, Georgetown University School of Medicine, Basic Science Building, Room 351, 3900 Reservoir Road NW, Washington DC 20007, USA.
Rosenthal
D S
DS
Luo
R
R
Smulson
M E
ME
D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016895:Culture Media, Serum-Free; D004256:DNA Polymerase I / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D051379:Mice; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics*; D015854:Up-Regulation
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016895:Culture Media, Serum-Free; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D011065:Poly(ADP-ribose) Polymerases; D004256:DNA Polymerase I