Interplay between PKCδ and Sp1 on Histone Deacetylase Inhibitor-Mediated Epstein-Barr Virus Reactivation

Epstein-Barr virus (EBV) undergoes latent and lytic replication cycles, and its reactivation from latency to lytic replication is initiated by expression of the two viral immediate-early transactivators, Zta and Rta. In vitro, reactivation of EBV can be induced by anti-immunoglobulin, tetradecanoyl phorbol acetate, and histone deacetylase inhibitor (HDACi). We have discovered that protein kinase C delta (PKC delta) is required specifically for EBV reactivation by HDACi. Overexpression of PKC delta is sufficient to induce the activity of the Zta promoter (Zp) but not of the Rta promoter (Rp). Deletion analysis revealed that the ZID element of Zp is important for PKC delta activation. Moreover, the Sp1 putative sequence on ZID is essential for PKC delta-induced Zp activity, and the physiological binding of Sp1 on ZID has been confirmed. After HDACi treatment, activated PKC delta can phosphorylate Sp1 at serine residues and might result in dissociation of the HDAC2 repressor from ZID. HDACi-mediated HDAC2-Sp1 dissociation can be inhibited by the PKC delta inhibitor, Rotterlin. Furthermore, overexpression of HDAC2 can suppress the HDACi-induced Zp activity. Consequently, we hypothesize that HDACi induces PKC delta activation, causing phosphorylation of Sp1, and that the interplay between PKC delta and Sp1 results in the release of HDAC2 repressor from Zp and initiation of Zta expression.