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 variet y of functions in the transformation of primary rodent cells and the r egulation of apoptosis and transcription. We have recently shown recen tly that the E1B 19 kDa protein from Adenovirus 5 (Ad 5) can functiona lly antagonize the stimulatory effect of E1A 13S on the human transcri ption factor NF-kappa B. Here we show that expression of E1B 19 kDa ne gatively interfered with the activation of NF-kappa B by different sti muli, such as the E1A 13S protein, and treatment with phorbol ester an d tumor necrosis factor alpha. This suggests that E1B 19 kDa acts on a common upstream signaling event. Band shift experiments showed that e xpression of E1B 19 kDa impaired the generation of the nuclear, DNA-bi nding form of NF-kappa B. Domain mapping experiments employing various E1B 19 kDa mutants revealed the necessity of a hydrophobic Bcl-2 homo logy region between amino acids 90 and 96 for NF-kappa B inhibition. C otransfection experiments showed that the inhibitory effect of E1B 19 kDa on E1A 13S-activated NF-kappa B transcription was gradually lost i n the course of time. Thus the continuous stimulatory action of E1A 13 S can finally override the antagonistic effects of E1B 19 kDa on NF-ka ppa B activity. In contrast to E1B 19 kDa, expression of the E1B 55 kD a protein did not result in a de novo activation of NF-kappa B, but co -stimulated the transcriptional potential of activated NF-kappa B.