The broad and long-term objectives of this application focus on elucidating the role of retinoids in viral latency. Human cytomegalovirus (HCMV) is of great societal significance and has become an important cause of morbidity and mortality for individuals in the clinical setting. particularly cancer patients, neonates and AIDS patients. Latent infection of humans is a very fundamental aspect of HCMV disease which may also significantly impact on the development of a number of human malignancies. Reactivation of latent virus is believed to result from a signal transduction event that induces immediate-early (lE) gene transcription. The three specific aims described in this proposal attempt to address the direct involvement of retinoids and their cognate nuclear receptors in regulating the HCMV major lE gene by Its promoter (MIEP). The first specific aim will involve an Investigation of the expression of the HCMV- MIEP in an established transgenic mouse model system that has the MIEP linked to the lacz reporter gene. Control animals that carry a mutant MIEP-RAREs lacz reporter gene will be generated. The expression profile of the MIEP-Lacz will be compared with the expression pattern of the various retinoic acid receptors (RARs) and should indicate whether a superimposition of MIEP expression and RARs expression exists. To examine whether the MIEP can be activated tn vivo by RA, transgenic mice will be administered with exogenous doses of RA and the induction of the MIEP will be determined. The second specific aim will elucidate the mechanisms underlying retinoid induction of the MIEP in an established human embryonal carcinoma (EC) cell system shown to be non-permissive in the uninduced state but replicates HCMV alter RA induction. Experiments are designed to precisely define the MIEP RA response elements and to investigate the direct interaction of the known RARs. The third specific aim will test for the involvement of the RARs in determining HCMV permissiveness by EC cell lines expressing trans-dominant negative retinoid receptors. These EC cell lines will be analyzed for their ability to inhibit RA induced HCMV replication. These proposed experiments should increase our knowledge of elements which lead to the activation of HCMV from latency and should provide insight in alternative methods for drug therapy.