Functional Antagonism Between the Retinoic Acid Receptor and the Viral Transactivator BZLF1 is Mediated by Protein-Protein Interactions

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 92; no. 26; pp. 12265 - 12269
• Main Authors: Pfitzner, E, Becker, P, Rolke, A, Schüle, R
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 19.12.1995; National Acad Sciences; National Academy of Sciences
• Subjects: 3T3 Cells; Animals; Antibodies; Base Sequence; Binding Sites; Biochemistry; Cell Line; Cercopithecus aethiops; COS cells; Dimerization; DNA; DNA-Binding Proteins - biosynthesis; DNA-Binding Proteins - isolation & purification; DNA-Binding Proteins - metabolism; Epstein-Barr virus; Glutathione Transferase - biosynthesis; Herpesvirus 4, Human - genetics; Herpesvirus 4, Human - metabolism; Immunoblotting; Mice; Molecular Sequence Data; NIH 3T3 cells; Plasmids; Proteins; Receptors, Retinoic Acid - biosynthesis; Receptors, Retinoic Acid - isolation & purification; Receptors, Retinoic Acid - metabolism; Recombinant Fusion Proteins - biosynthesis; Recombinant Proteins - biosynthesis; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Repression; Retinoic Acid Receptor alpha; Trans-Activators - biosynthesis; Trans-Activators - isolation & purification; Trans-Activators - metabolism; Transactivation; Transcriptional Activation; Transfection; Viral Proteins - metabolism; Viruses
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.26.12265

The Epstein-Barr virus-encoded protein BZLF1 is a member of the basic leucine zipper (bZip) family of transcription factors. Like several other members of the bZip family, transcriptional activity of BZLF1 is modulated by retinoic acid receptors (RARs). We present evidence that the RARα and BZLF1 can reciprocally repress each other's transcriptional activation by a newly discovered mechanism. Analysis of RARα mutants in transfection studies reveals that the DNA binding domain is sufficient for inhibition of BZLF1 activity. Analysis of BZLF1 mutants indicates that both the coiled-coil dimerization domain and a region containing the transcriptional activation domain of BZLF1 are required for transrepression. Coimmunoprecipitation experiments demonstrate physical interactions between RARα and BZLF1 in vivo. Furthermore, glutathione S-transferase-pulldown assays reveal that these protein-protein interactions are mediated by the coiled-coil dimerization domain of BZLF1 and the DNA binding domain of RARα. While RARα is unable to recognize BZLF1 binding sites, the RARα can be tethered to the DNA by forming a heteromeric complex with BZLF1 bound to DNA. Tethering RARs via protein-protein interactions onto promoter DNA suggest a mechanism through which RARs might gain additional levels of transcriptional regulation.