The human tumour suppressor protein p53 is an effective inhibitor of cell growth, by inducing cell cycle arrest and apoptosis. However, p53-induced cell growth inhibition can be detrimental for virus multiplication. Therefore, viruses encode for proteins, which can interfere with the functions of the p53 protein. Human adenoviruses encode for a transcription repressor protein named E1B-55K, which inhibits the activity of the p53 protein during a lytic adenovirus infection. In this thesis, we have studied the biochemical characteristics of the E1B-55K protein and how the E1B-55K protein interferes with the function of p53 as a transcription factor. Our data show that the E1B-55K protein interacts with the Sin3 co-repressor complex in adenovirus transformed and in adenovirus infected cells. Furthermore, the E1B-55K protein recruites a histone deacetylase activity, indicating that the E1B-55K protein is associated with a functional chromatin modifying complex. We also show that in addition to repressing p53-activated transcription, E1B-55K could also relieve p53-mediated repression of the survivin and Map4 promoters. Previous results have shown that E1B-55K inhibits p53 as a transcriptional activator of the p21/CDKN1A promoter. Here we show that the E1B-55K protein prevents p53 from inducing histone H3 and H4 acetylation on p21/CDKN1A promoter, which coincided with the inhibition of p21/CDKN1A protein expression. Notably, the Sin3 complex was detected in the vicinity of the p53 binding site on the p21/CDKN1A promoter, suggesting that the E1B-55K protein blocked p53-mediated histone acetylation by recruitment of a histone deacetylase activity. Inhibition of p21/CDKN1A protein expression might be the reason, why the E1B-55K protein alleviates p53-dependent transcriptional repression of the survivin promoter. Finally, we show that oligomerisation of the E1B-55K protein is important for the defined subcellular localization of the protein and for its function as a repressor of p53-activated transcription.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-3887 |
| Date | January 2003 |
| Creators | Punga, Tanel |
| Publisher | Uppsala universitet, Institutionen för medicinsk biokemi och mikrobiologi, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, 0282-7476 ; 1314 |
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