Evidence for a cancer-specific switch at the CDK4 promoter with loss of control by both USF and c-Myc.
USF and c-Myc are basic helix-loop-helix transcription factors with similar DNA-binding specificities, but antagonistic effects on cellular transformation. In order to determine how these opposite functions correlate with the transcriptional activities of the two factors on particular downstream targets, we investigated the roles of USF and c-Myc in expression of CDK4, a known direct target of c-Myc. Overexpression of either c-Myc or USF2, but not USF1, stimulated the expression of CDK4 promoter-driven reporter genes in the non-tumorigenic mammary epithelial MCF-10A cells. Dominant-negative mutants specific to either Myc or USF family proteins inhibited reporter gene activity as well as endogenous CDK4 expression, demonstrating involvement of both USF and Myc in CDK4 transcriptional control. In contrast, in two different breast cancer cell lines where USF is transcriptionally inactive and c-Myc is overexpressed, CDK4 promoter activity was no longer responsive to either transcription factor. Accordingly, chromatin immunoprecipitation revealed significantly lower levels of both USF and c-Myc bound to the endogenous CDK4 promoter in breast cancer cells than in MCF-10A cells, with a concomitant decrease in associated histone H3 acetylation. These results suggest that a major switch in the transcriptional control of CDK4 occurs during breast carcinogenesis, with likely alteration of cell cycle regulation.
Pawar
Snehalata A
SA
Department of Molecular Genetics, The University of Texas, MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
Szentirmay
Marilyn N
MN
Hermeking
Heiko
H
Sawadogo
Michèle
M
D001483:Base Sequence; D001665:Binding Sites; D001940:Breast / Q000166:cytology / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002843:Chromatin / Q000235:genetics; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D015533:Transcriptional Activation; D051720:Upstream Stimulatory Factors
D002843:Chromatin; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D014157:Transcription Factors; C497181:USF1 protein, human; C497184:USF2 protein, human; D051720:Upstream Stimulatory Factors; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases