Insertion of an exogenous promoter in the E1A regulatory region of adenovirus does not disturb viral replication despite reduced E1A transcription

Insertion of an exogenous promoter into adenoviral regulatory regions may result in altered specificity and activity of the integrated promoter-mediated transcription in the context of recombinant adenoviruses (Ad). The alteration is due to the influence of the viral regulatory elements. Specificity of oncolytic Ad, in which the E1A expression is designed to be controlled by a tumor-specific promoter, could thus be modulated by the Ad E1A enhancer/promoters. We prepared recombinant Ad bearing a midkine (MK) promoter region in the 3′-side of the E1A promoter and investigated the relationship between transcriptional activity by the E1A promoter-fused MK fragment and the viral replication. Reporter assays revealed that the transcriptional activity of the fused E1A-MK fragment was significantly lower than that of respective E1A and the MK promoters. However, the replication of the Ad bearing the MK promoter was greater than or comparable to that of wild-type Ad. The present study suggests that the replication of oncolytic Ad in tumors is not directly correlated with the promoter activity to transcribe the E1A gene and that insertion of an exogenous promoter downstream to the E1A regulatory region may not always disturb Ad replication.