A hydrophobic region within the adenovirus E1B 19 kDa protein is necessary for the transient inhibition of NF-kappa B activated by different stimuli

The early transcribed adenovirus proteins E1A and E1B display a variety of functions in the transformation of primary rodent cells and the regulation of apoptosis and transcription. We have recently shown recently that the E1B 19 kDa protein from Adenovirus 5 (Ad 5) can functionally antagonize the stimulatory effect of E1A 13S on the human transcription factor NF-kappa B. Here we show that expression of E1B 19 kDa negatively interfered with the activation of NF-kappa B by different stimuli, such as the E1A 13S protein, and treatment with phorbol ester and tumor necrosis factor alpha. This suggests that E1B 19 kDa acts on a common upstream signaling event. Band shift experiments showed that expression of E1B 19 kDa impaired the generation of the nuclear, DNA-binding form of NF-kappa B. Domain mapping experiments employing various E1B 19 kDa mutants revealed the necessity of a hydrophobic Bcl-2 homology region between amino acids 90 and 96 for NF-kappa B inhibition. Cotransfection experiments showed that the inhibitory effect of E1B 19 kDa on E1A 13S-activated NF-kappa B transcription was gradually lost in the course of time. Thus the continuous stimulatory action of E1A 13S can finally override the antagonistic effects of E1B 19 kDa on NF-kappa B activity. In contrast to E1B 19 kDa, expression of the E1B 55 kDa protein did not result in a de novo activation of NF-kappa B, but co-stimulated the transcriptional potential of activated NF-kappa B.