Abstract 16634: p300 is Required for the DNA Damage Response Through Acetylation of Histone H3K56
Background: The nuclear acetyltransferase p300 is a chromatin-modifying enzyme that programs gene expression in response to extracellular and intracellular signals. p300 has been implicated in transcription-dependent DNA damage repair. Aging and genotoxic stress are associated with similar reductions in histone acetylation and p300 HAT activity. Acetylation of Histone H3 at Lysine 56 (H3K56) by p300 has been suggested to be important for initiation of DNA damage response.
Hypothesis: We hypothesize that p300 confers cardioprotection against genotoxic/oxidative stress by faciliating the DNA damage response.
Methods: Physiologic parameters and survival were determined in heterozygous p300 -/+ mice. p300 knockdown (p300KD) was achieved in neonatal cardiac myocytes with p300-targeting siRNA and compared to a non-targeting control (NS). Genotoxic/oxidative stress was induced with doxorubicin (Dox) 1µM. Cycloheximide (CY, 5ug/ml) was used to assess p300 stability.
Results: In cultured cardiac myocytes, DOX caused rapid, sustained p300 stabilization (3.7±1.9 fold vs. control at 8h; p<0.05). p300KD significantly increased DOX-induced myocyte death (26.9±13.5%; p<0.05) and caspase3 cleavage, while blunting specific DNA damage responses, including reduced phosphorylation of H2AX, ATM, and BRCA1, and reduced phosphorylation and acetylation of p53. Further, p300KD greatly reduced DOX-induced acetylation of H3K56 (67.2±17.5%; p<0.01). Converse effects were seen with activation of p300 by HDAC inhibitors TSA and SAHA. Also, p300KD ablated TSA/SAHA enhanced DNA damage response and cardioprotection. Consistent with a role for DNA damage in aging, mice with heterozygous global p300 loss exhibited an accelerated aging phenotype, with hair thinning and graying, reduced bone density, dermal thinning, increased beta galactosidase activity and immunoreactivity for p16ink, elevated glucose and significantly shortened lifespan (≤ 1 y) without evidence of systemic disease.
Conclusion: Genotoxic stress causes a post-transcriptional stabilization of p300 that is required for the DNA damage response, preventing cell death and apoptosis. These findings likely account for the accelerated aging phenotype associated with p300 loss.
- © 2011 by American Heart Association, Inc.