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Constitutive DNase I hypersensitivity of p53-regulated promoters
Corey D Braastad1, Zhiyong Han, Eric A Hendrickson
1Department of Molecular Biology, Cellular Biology and Biochemistry, Brown University, Providence, Rhode Island 02912, USA.
Abstract:
The ability of p53 to alter, at the transcriptional level, the gene expression of downstream targets is critical for its role as a tumor suppressor. Most models of p53 activation postulate the stepwise recruitment by p53 of coactivators, histone acetyltransferases, and/or chromatin remodeling factors to a promoter region to facilitate the subsequent access of the general transcriptional machinery required for transcriptional induction. We demonstrate here, however, that the promoter regions for the p53 target genes, p21, 14-3-3sigma, and KARP-1, exist in a constitutively open conformation that is readily accessible to DNase I. This conformation was not altered by DNA damage or by whether p53 was present or absent in the cell. In contrast, p53 response elements, which resided outside the immediate promoter regions, existed within DNase I-resistant chromatin domains. Thus, p53 activation of downstream target genes occurs without p53 inducing chromatin alterations detectable by DNase I accessibility at either the promoter or the response element. As such, these data support models of p53 activation that do not require extensive chromatin alterations to support cognate gene expression.
Insights
The tumor suppressor p53 activates genes without altering chromatin structure. Promoter regions remain open, and p53 binding sites are resistant to DNase I, challenging existing models of gene activation.
Area of Science:
- Molecular Biology
- Cancer Research
- Epigenetics
Background:
- The tumor suppressor protein p53 is crucial for regulating gene expression in response to DNA damage.
- Conventional models propose p53 recruits chromatin-modifying factors to activate target genes.
- These factors are thought to remodel chromatin, allowing transcriptional machinery access.
Purpose of the Study:
- To investigate the chromatin state of p53 target genes.
- To determine if p53 activation involves chromatin alterations.
- To challenge or support existing models of p53-mediated transcriptional regulation.
Main Methods:
- DNase I accessibility assays were used to probe chromatin structure.
- Analysis focused on promoter regions and p53 response elements of target genes (p21, 14-3-3sigma, KARP-1).
- Experiments were conducted in the presence and absence of DNA damage and p53.
Main Results:
- Promoter regions of p53 target genes (p21, 14-3-3sigma, KARP-1) are constitutively open and accessible to DNase I.
- This accessibility is independent of DNA damage or p53 presence.
- p53 response elements are located within DNase I-resistant chromatin domains.
Conclusions:
- p53 activates downstream target genes without inducing detectable chromatin alterations at promoters or response elements.
- These findings suggest p53-mediated transcription can occur without extensive chromatin remodeling.
- The study supports models of p53 activation that do not rely on significant chromatin modifications.