Modulation of E2F activity is linked to interferon-induced growth suppression of hematopoietic cells.
E2F is a heterodimeric transcription factor that controls transcription of several growth-regulatory genes including cdc2. To investigate the mechanism of interferon-alpha (IFN-alpha)-mediated growth suppression of hematopoietic cells, we examined the effect of IFN-alpha on the expression and function of E2F using IFN-sensitive Daudi cells. Down-regulation of E2F-1, a subunit of E2F, was observed after 8 h of culture with IFN-alpha; expression of E2F-4, another subunit of E2F, and DP-1, a heterodimeric partner of E2F, was unaffected. Gel shift assays revealed that the DNA binding activity of free E2F, which is composed of E2F-1 and E2F-4, was inhibited by IFN-alpha. In contrast, IFN-alpha did not affect the DNA binding ability of E2F-1 and E2F-4 in a complex with retinoblastoma (RB) susceptibility gene family proteins including pRB, p107, and p130. IFN-alpha could induce dephosphorylation of pRB, thereby turning active E2F-pRB complexes into transcriptional repressors. Transient chloramphenicol acetyltransferase assays revealed that the activity of the E2F-dependent cdc2 promoter was suppressed by IFN-alpha. These results suggest that the antiproliferative action of IFN-alpha is mediated through the modulation of E2F activity in two different ways: down-regulation of transcriptionally active free E2F and conversion of E2F-pRB complexes into transcriptional repressors.
Iwase
S
S
Division of Hemopoiesis, Institute of Hematology, and the Department of Hematology, Jichi Medical School, Tochigi 329-04, Japan.
Furukawa
Y
Y
Kikuchi
J
J
Nagai
M
M
Terui
Y
Y
Nakamura
M
M
Yamada
H
H
D000998:Antiviral Agents / Q000494:pharmacology*; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002352:Carrier Proteins; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D010766:Phosphorylation; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism*
D000998:Antiviral Agents; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D016898:Interferon-alpha; D016271:Proto-Oncogene Proteins c-myc; D056465:Retinoblastoma-Binding Protein 1; C493735:TFDP1 protein, human; D050680:Transcription Factor DP1; D014157:Transcription Factors; D016203:CDC2 Protein Kinase