Abstract
The tumor suppressor protein p53 and the adenoviral 12 S E1A oncoprotein are both known to elicit their biological effects mainly by regulating the transcription of important cellular genes. The human proliferating cell nuclear antigen (PCNA) gene is a transcriptional target of both p53 and E1A. We have analyzed the effects of p53 and 12 S E1A, separately as well as together, on PCNA gene transcription. Our results showed that whereas both p53 and 12 S E1A separately activated PCNA transcription, 12 S E1A repressed p53-mediated transcriptional activation. Thus, 12 S E1A uses a dual strategy of transcriptional activation and repression to take control of the cellular PCNA gene regulation. The cyclic AMP-response element in the PCNA core promoter, besides being crucial for basal transcription, synergizes with p53 to activate transcription. The cyclic AMP response element-binding protein (CREB)-binding protein (CBP) is an essential component of both the transcriptional activation and repression by E1A. Our data demonstrate for the first time that E1A can modulate CBP function to activate PCNA transcription, while at the same time repressing p53-mediated activation by disrupting CBP interaction with p53, thereby uncoupling PCNA transcription from the regulatory effects of p53.
Highlights
The tumor suppressor protein p53 and the adenoviral 12 S E1A oncoprotein are both known to elicit their biological effects mainly by regulating the transcription of important cellular genes
We show that CBP is involved both in E1A-mediated and p53-mediated transcriptional activation of the proliferating cell nuclear antigen (PCNA) gene
We have analyzed the mechanism of transcriptional regulation of the human PCNA gene by p53 and adenoviral 12 S E1A proteins
Summary
The tumor suppressor protein p53 and the adenoviral 12 S E1A oncoprotein are both known to elicit their biological effects mainly by regulating the transcription of important cellular genes. Experiments using Saos-2 (p53Ϫ/Ϫ) cells and the PCNA gene promoter enabled us to analyze the transcriptional effects of these two proteins individually as well as in the presence of each other.
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