The PKC targeting protein RACK1 interacts with the Epstein-Barr virus activator protein BZLF1.
Phorbol esters reactivate Epstein-Barr virus (EBV) from latently infected cells via transcriptional activation of the viral immediate-early gene BZLF1. BZLF1 is a member of the extended AP-1 family of transcription factors that binds to specific BZLF1-binding motifs within early EBV promoters and to consensus AP-1 sites. Regulation of BZLF1's activity is achieved at the transcriptional level as well as through post-translational modifications. Recently, we reported that the transcriptional activity of BZLF1 is augmented by TPA [Baumann, M., Mischak, H., Dammeier, S., Kolch, W., Gires, O., Pich, D., Zeidler, R., Delecluse, H. J. & Hammerschmidt, W., (1998) J. Virol. 72, 8105-8114]. The increase of BZLF1's activity depends on a single serine residue (S186) that is phosphorylated by protein kinase C (PKC) in vitro and in vivo after stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). Here, we identified RACK1 as a binding partner of BZLF1 in a yeast interaction trap assay. RACK stands for receptor of activated C-kinase and is involved in targeting activated PKCs and other signaling proteins. In vivo, RACK1 binds directly to the transactivation domain of BZLF1. Although a functional relationship between BZLF1 and PKC could be mediated by RACKs, RACK1 did not have a detectable effect on the phosphorylation status of BZLF1 in in vitro or in vivo phosphorylation assays. We suggest that RACK1 may act as a scaffolding protein on BZLF1 independently of activated PKCs.
Baumann
M
M
GSF-National Research Center for Environment and Health, Institute of Clinical Molecular Biology and Tumor Genetics, Department of Gene Vectors, München, Germany.
Gires
O
O
Kolch
W
W
Mischak
H
H
Zeidler
R
R
Pich
D
D
Hammerschmidt
W
W
D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000378:metabolism*
C063676:BZLF1 protein, Herpesvirus 4, Human; D004268:DNA-Binding Proteins; D010455:Peptides; D000075370:Receptors for Activated C Kinase; D015534:Trans-Activators; D014764:Viral Proteins; C070301:peptide I; D011493:Protein Kinase C