Interferons and interleukin-6 suppress the DNA-binding activity of E2F in growth-sensitive hematopoietic cells.
Transcription factor E2F binds to cellular promoters of certain growth- and cell cycle-controlling genes and forms distinct heteromeric complexes with other nuclear proteins. We show here that alpha and beta interferons (alpha, beta) and interleukin-6 abolished the E2F-containing DNA-binding complexes in Daudi Burkitt lymphoma cells and in M1 myeloblastic cells, which responded to the cytokines by suppression of c-myc transcription. Time kinetics studies showed that the abolishment of E2F complexes coincided with reduction of c-myc expression and that both molecular events preceded the cell cycle block in G0/G1 phase. In contrast, the pattern of E2F complexes remained unchanged in an interferon-treated growth-resistant Daudi cell mutant that displayed relaxed regulation of c-myc. All of the DNA-binding E2F complexes, including those containing the retinoblastoma protein (pRB), cyclin A-p33cdk2, and the free forms of E2F, were reduced by interferons or interleukin-6. Their abolishment was unperturbed by pharmacological treatments that alleviated the cyclin A and pRB responses to interferon. Thus, changes in cyclin A expression and pRB phosphorylation are not primary events that influence the pattern of E2F responses to cytokines. Addition of EDTA to cell extracts of interferon-treated Daudi cells restored the DNA-binding activity of E2F, resulting in the appearance of a single E2F complex that exclusively contained pRB. It is suggested that the regulation of E2F by growth-inhibitory cytokines that induce cell cycle exit takes place at the level of the DNA-binding activity, and by that mean it differs basically from the phase-specific regulation of E2F in cycling cells.
Melamed
D
D
Department of Molecular Genetics and Virology, Weizmann Institute of Science, Rehovot, Israel.
Tiefenbrun
N
N
Yarden
A
A
Kimchi
A
A
D001483:Base Sequence; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002455:Cell Division; D002460:Cell Line; D016213:Cyclins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050684:E2F Transcription Factors; D004492:Edetic Acid / Q000494:pharmacology; D015870:Gene Expression; D016259:Genes, myc; D006801:Humans; D066298:In Vitro Techniques; D007372:Interferons / Q000494:pharmacology*; D015850:Interleukin-6 / Q000494:pharmacology*; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism*
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D015850:Interleukin-6; D009838:Oligodeoxyribonucleotides; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D007372:Interferons; D004492:Edetic Acid; D008274:Magnesium