Author ORCID Identifier

0000-0001-7925-3024

Date of Graduation

12-2018

Document Type

Dissertation (PhD)

Program Affiliation

Genes and Development

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Xiaobing Shi

Committee Member

Michelle C. Barton

Committee Member

Mark T. Bedford

Committee Member

Lauren A. Byers

Committee Member

Sharon Y.R. Dent

Committee Member

Boyi Gan

Abstract

Transcription is strictly regulated by numerous factors including transcription coactivators. The p300 protein and its close paralogue CREB-binding protein (CREBBP, aka CBP) are well-known transcriptional coactivators that have intrinsic lysine acetyltransferase activity. The functions of p300/CBP largely rely on their capabilities to bind to chromatin and to acetylate the histone substrates. However, the molecular mechanisms underlying the regulation of these processes are not fully understood.

Through combination of various biochemical, biophysical and molecular approaches, we show that the ZZ-type zinc finger (ZZ) domain of p300 functions as a histone reader that specifically binds the N-terminal tail of histone H3. Crystal structure of p300 ZZ in complex with the H3 peptide reveals that the ZZ domain adopts a negatively charged cavity to anchor Ala1 and Arg2 of H3. The ZZ-H3 interaction is not sensitive to common post-translational modifications, such as methylation or acetylation, on the H3 tail. Both in vitro and cell-based assays reveal that p300 ZZ domain, together with bromodomain (BRD), is important in recruiting p300 to chromatin. As a module adjacent to the histone acetyltransferase (HAT) domain, ZZ domain is also required for efficient histone acetylation by HAT. The recognition of histone H3 by the ZZ domain selectively promotes p300-dependent acetylation specifically on histone H3K27 and H3K18, whereas the acetyllysine binding activity of BRD is required for acetylation of virtually all lysine residues in H3 and H4 tails.

p300/CBP are frequently mutated or dysregulated in many human diseases including cancer. We found that p300 is overexpressed in small cell lung cancer (SCLC), the most aggressive subtype of lung cancer. By CRISPR/Cas9-mediated gene manipulation, we found that p300 depletion impedes proliferation of human and mouse SCLC cells whereas CBP depletion has little or no effect. Depletion of p300 reduces the expression of critical oncogenes such as the MYC family genes, indicating that p300 promotes SCLC cell growth by sustaining oncogene expression.

In summary, we identified the ZZ domain of p300 as a novel histone H3 reader that is critical for the chromatin association and enzymatic activity of p300. Recognition of H3 by ZZ domain is important to the functions of p300 in human cancer.

Keywords

epigenetics, p300/CBP, histone acetylation, histone reader, small cell lung cancer

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