The myocyte enhancer factor-2 (MEF2) family of transcription factors has important roles in the development and function of T cells, neuronal cells and muscle cells. MEF2 is capable of repressing or activating transcription by association with a variety of co-repressors or co-activators in a calcium-dependent manner. Transcriptional repression by MEF2 has attracted particular attention because of its potential role in hypertrophic responses of cardiomyocytes. Several MEF2 co-repressors, such as Cabin1/Cain and class II histone deacetylases (HDACs), have been identified. However, the molecular mechanism of their recruitment to specific promoters by MEF2 remains largely unknown. Here we report a crystal structure of the MADS-box/MEF2S domain of human MEF2B bound to a motif of the transcriptional co-repressor Cabin1 and DNA at 2.2 A resolution. The crystal structure reveals a stably folded MEF2S domain on the surface of the MADS box. Cabin1 adopts an amphipathic alpha-helix to bind a hydrophobic groove on the MEF2S domain, forming a triple-helical interaction. Our studies of the ternary Cabin1/MEF2/DNA complex show a general mechanism by which MEF2 recruits transcriptional co-repressor Cabin1 and class II HDACs to specific DNA sites.
"This interaction is mediated by a short amphipathic helix conserved in the N-terminal regulatory domain of class IIa HDACs. Crystallography analyses and in vitro biochemical studies reveal that the amphipathic helix binds to a highly conserved hydrophobic groove on the MADS-box/MEF2 domain of MEF2 (19–21). These studies suggest that small molecules binding to the hydrophobic pocket of MEF2 could block the recruitment of class IIa HDACs to DNA, thereby inhibiting the function of class IIa HDACs. "
[Show abstract][Hide abstract] ABSTRACT: Enzymes that modify the epigenetic status of cells provide attractive targets for therapy in various diseases. The therapeutic development of epigenetic modulators, however, has been largely limited to direct targeting of catalytic active site conserved across multiple members of an enzyme family, which complicates mechanistic studies and drug development. Class IIa histone deacetylases (HDACs) are a group of epigenetic enzymes that depends on interaction with Myocyte Enhancer Factor-2 (MEF2) for their recruitment to specific genomic loci. Targeting this interaction presents an alternative approach to inhibiting this class of HDACs. We have used structural and functional approaches to identify and characterize a group of small molecules that indirectly target class IIa HDACs by blocking their interaction with MEF2 on DNA.Weused X-ray crystallography and (19)F NMRto show that these compounds directly bind to MEF2. We have also shown that the small molecules blocked the recruitment of class IIa HDACs to MEF2-targeted genes to enhance the expression of those targets. These compounds can be used as tools to study MEF2 and class IIa HDACs in vivo and as leads for drug development.
Nucleic Acids Research 03/2012; 40(12):5378-88. DOI:10.1093/nar/gks189 · 9.11 Impact Factor
"A couple of structures are available for dimers of MADS domains (followed by a domain with some homology to the I domain) [33-38], but structural information for the other domains is lacking. The structures show that two MADS domains extensively contact each other, but mutagenesis data indicate that also other parts of the MIKC proteins contact each other. "
[Show abstract][Hide abstract] ABSTRACT: Plant MADS domain proteins are involved in a variety of developmental processes for which their ability to form various interactions is a key requisite. However, not much is known about the structure of these proteins or their complexes, whereas such knowledge would be valuable for a better understanding of their function. Here, we analyze those proteins and the complexes they form using a correlated mutation approach in combination with available structural, bioinformatics and experimental data.
Correlated mutations are affected by several types of noise, which is difficult to disentangle from the real signal. In our analysis of the MADS domain proteins, we apply for the first time a correlated mutation analysis to a family of interacting proteins. This provides a unique way to investigate the amount of signal that is present in correlated mutations because it allows direct comparison of mutations in various family members and assessing their conservation. We show that correlated mutations in general are conserved within the various family members, and if not, the variability at the respective positions is less in the proteins in which the correlated mutation does not occur. Also, intermolecular correlated mutation signals for interacting pairs of proteins display clear overlap with other bioinformatics data, which is not the case for non-interacting protein pairs, an observation which validates the intermolecular correlated mutations. Having validated the correlated mutation results, we apply them to infer the structural organization of the MADS domain proteins.
Our analysis enables understanding of the structural organization of the MADS domain proteins, including support for predicted helices based on correlated mutation patterns, and evidence for a specific interaction site in those proteins.
"CNS defects could provide a major contribution. The repressive action of Cabin1 on calcineurin in both the mature CNS (Lai et al., 2000) and immune system (Jang et al., 2007a) and on MEF2 in the immune system (Sun et al., 1998; Youn et al., 1999; Han et al., 2003; Pan et al., 2005; Jang et al., 2007b) leave open the possibility that Cabin1 repression of these pathways also plays a broad role during the development of both tissues. In T-cells, Cabin1 acts as a repressor of calcineurin and MEF2 under normal conditions, but repression is alleviated in response to elevated levels of intracellular calcium (Youn et al., 1999). "
[Show abstract][Hide abstract] ABSTRACT: Nervous system assembly and function depends on precise regulation of developmental gene expression. Cabin1, an essential gene in developing mice, is enriched in regions of the developing zebrafish central nervous system (CNS). Cabin1 is a repressor of MEF2- (myocyte enhancer factor 2) and calcineurin-mediated transcription in the immune system, but its function in the CNS during development is unknown. We identified Cabin1 from a library of genes enriched in developing neurons and determined the temporal and spatial expression of Cabin1 mRNA during CNS development. We found Cabin1 mRNA expression in the developing brain at times correlated with later aspects of neuronal differentiation. In some regions of the CNS Cabin1 expression overlaps with regions that also express proteins known to interact with Cabin1: MEF2 and/or calcineurin. We suggest that Cabin1 could act as a regulator of MEF2 and calcineurin activity in the developing nervous system, given their roles in neuronal differentiation and synaptic refinement.
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