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Proc Natl Acad Sci U S A. 2009 May 26;106(21):8513-8. doi: 10.1073/pnas.0902873106. Epub 2009 May 11.

A tumor suppressive coactivator complex of p53 containing ASC-2 and histone H3-lysine-4 methyltransferase MLL3 or its paralogue MLL4.

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1
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

Abstract

ASC-2, a multifunctional coactivator, forms a steady-state complex, named ASCOM (for ASC-2 COMplex), that contains the histone H3-lysine-4 (H3K4)-methyltransferase MLL3 or its paralogue MLL4. Somewhat surprisingly, given prior indications of redundancy between MLL3 and MLL4, targeted inactivation of the MLL3 H3K4-methylation activity in mice is found to result in ureter epithelial tumors. Interestingly, this phenotype is exacerbated in a p53(+/-) background and the tumorigenic cells are heavily immunostained for gammaH2AX, indicating a contribution of MLL3 to the DNA damage response pathway through p53. Consistent with the in vivo observations, and the demonstration of a direct interaction between p53 and ASCOM, cell-based assays have revealed that ASCOM, through ASC-2 and MLL3/4, acts as a p53 coactivator and is required for H3K4-trimethyation and expression of endogenous p53-target genes in response to the DNA damaging agent doxorubicin. In support of redundant functions for MLL3 and MLL4 for some events, siRNA-mediated down-regulation of both MLL3 and MLL4 is required to suppress doxorubicin-inducible expression of several p53-target genes. Importantly, this study identifies a specific H3K4 methytransferase complex, ASCOM, as a physiologically relevant coactivator for p53 and implicates ASCOM in the p53 tumor suppression pathway in vivo.

PMID:
19433796
PMCID:
PMC2689008
DOI:
10.1073/pnas.0902873106
[Indexed for MEDLINE]
Free PMC Article
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