Physical and functional interaction of the Epstein-Barr virus BZLF1 transactivator with the retinoic acid receptors RAR alpha and RXR alpha.

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Epstein-Barr virus (EBV) reactivation, indicated by induction of EBV early antigens from latently infected lymphoid cell lines by phorbol esters, is inhibited by retinoic acid (RA). Viral reactivation, which is triggered by the immediate-early BZLF-1 (Z) viral gene product, is repressed by retinoic acid receptors (RARs) RAR alpha and RXR alpha. These proteins negatively regulate Z-mediated transactivation of the promoter for an EBV early gene product, early antigen-diffuse (EaD). Here we confirm a direct physical interaction between the AP1-like protein Z and RXR alpha and map the domains of interaction in the Z protein and RXR alpha. The domain required for homodimerization of Z is separate from that required for its interaction with RXR alpha. Z also has the effect of repressing activation of an RAR-responsive cellular promoter (BRE). Point mutants in the dimerization domain of Z unable to interact with RXR alpha do not repress RXR alpha-mediated transactivation of BRE, the promoter for RAR beta, which suggests that interaction between the two proteins is required for this repressor effect. The domain of RXR alpha required for interaction with Z has been mapped, and is again separate from that required for homodimerization. These results indicate that a 'cross-coupling' or direct interaction between Z and RAR alpha and RXR alpha can modulate the reactivation of latent EBV infection and suggest that, reciprocally, the viral protein Z may influence cellular regulatory pathways.

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