The Adenovirus E1A-Regulated Transcription Factor E4F Is Generated from the Human Homolog of Nuclear Factor ϕAP3

• Published in: Molecular and cellular biology Vol. 17; no. 4; pp. 1890 - 1903
• Main Authors: Fernandes, Elma R., Rooney, Robert J.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 01.04.1997
• Subjects: adenovirus
• ISSN: 1098-5549; 0270-7306; 1098-5549
• DOI: 10.1128/MCB.17.4.1890

A 50-kDa cellular factor, E4F, has been implicated in mediating trans activation of the adenovirus E4 gene by the 289R E1A (13S) protein. Previous experiments demonstrated an E1A-dependent increase in E4F DNA binding activity, dependent on phosphorylation, that correlated with the activation of E4 transcription. Using expression screening, we isolated a cDNA clone encoding the E4F protein, as judged by DNA binding characteristics, transcriptional activation, and immunological criteria. The E4F-1 cDNA encodes a 783-amino-acid polypeptide that has 86% sequence identity with the murine nuclear factor ϕAP3, a GLI-krüppel-related protein. E4F DNA binding activity is encoded within an amino-terminal region of E4F-1 that contains a zinc finger domain and, as with endogenous E4F, is phosphatase sensitive. We found that E4F was generated from the full-length E4F-1-encoded protein as a 50-kDa amino-terminal fragment. Moreover, E1A (13S) expression induced the phosphorylation of both forms of E4F-1 but differentially regulated their DNA binding activities, stimulating the 50-kDa fragment while reducing the activity of the full-length protein. In transient-transfection assays, the E4F-1 amino-terminal fragment stimulated the adenovirus E4 promoter in the presence of E1A (13S) , whereas the full-length protein repressed the promoter in the absence, but not the presence, of E1A. The results indicate that the 50-kDa polypeptide responsible for E4F DNA binding activity is a fragment generated from the human homolog of ϕAP3 and that the two forms of the E4F-1 protein are differentially regulated by E1A through phosphorylation.