ISWI chromatin remodeling complexes in the DNA damage response.
Ontology highlight
ABSTRACT:
SUBMITTER: Aydin OZ
PROVIDER: S-EPMC4615051 | biostudies-other | 2014
REPOSITORIES: biostudies-other
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Project description:ISWI proteins form the catalytic core of a subset of ATP-dependent chromatin remodeling activities in eukaryotes from yeast to man. Many of these complexes have been found to reposition nucleosomes but with different directionalities. We find that the yeast Isw1a, Isw2, and Chd1 enzymes preferentially move nucleosomes toward more central locations on short DNA fragments whereas Isw1b does not. Importantly, the inherent positioning properties of the DNA play an important role in determining where nucleosomes are relocated to by all of these enzymes. However, a key difference is that the Isw1a, Isw2, and Chd1 enzymes are unable to move nucleosomes to positions closer than 15 bp from a DNA end, whereas Isw1b can. We also find that there is a correlation between the inability of enzymes to move nucleosomes close to DNA ends and the preferential binding to nucleosomes bearing linker DNA. These observations suggest that the accessibility of linker DNA together with the positioning properties of the underlying DNA play important roles in determining the outcome of remodeling by these enzymes.
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Project description:The Williams Syndrome Transcription Factor (WSTF), the product of the WBSCR9 gene, is invariably deleted in the haploinsufficiency Williams-Beuren Syndrome. Along with the nucleosome-dependent ATPase ISWI, WSTF forms a novel chromatin remodeling complex, WICH (WSTF-ISWI chromatin remodeling complex), which is conserved in vertebrates. The WICH complex was purified to homogeneity from Xenopus egg extract and was found to contain only WSTF and ISWI. In mouse cells, WSTF interacts with the SNF2H isoform of ISWI. WSTF accumulates in pericentric heterochromatin coincident with the replication of these structures, suggesting a role for WSTF in the replication of heterochromatin. Such a role is supported by the in vitro activity of both the mouse and frog WICH complexes: they are involved in the assembly of regular spaced nucleosomal arrays. In contrast to the related ISWI-interacting protein ACF1/WCRF180, WSTF binds stably to mitotic chromosomes. As dysfunction of other chromatin remodeling factors often has severe effects on development, haploinsufficiency of WSTF may explain some of the phenotypes associated with this disease.
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Project description:Chromatin remodeling complexes can translocate nucleosomes along the DNA in an ATP-dependent manner. Here, we studied autofluorescent protein constructs of the human ISWI family members Snf2H, Snf2L, the catalytically inactive Snf2L+13 splice variant, and the accessory Acf1 subunit in living human and mouse cells by fluorescence microscopy/spectroscopy. Except for Snf2L, which was not detected in the U2OS cell line, the endogenous ISWI proteins were abundant at nuclear concentrations between 0.14 and 0.83 μM. A protein interaction analysis showed the association of multimeric Snf2H and Acf1 into a heterotetramer or higher-order ACF complex. During the G1/2 cell cycle phase, Snf2H and Snf2L displayed average residence times <150 ms in the chromatin-bound state. The comparison of active and inactive Snf2H/Snf2L indicated that an immobilized fraction potentially involved in active chromatin remodeling comprised only 1-3%. This fraction was largely increased at replication foci in S phase or at DNA repair sites. To rationalize these findings we propose that ISWI remodelers operate via a "continuous sampling" mechanism: The propensity of nucleosomes to be translocated is continuously tested in transient binding reactions. Most of these encounters are unproductive and efficient remodeling requires an increased binding affinity to chromatin. Due to the relatively high intranuclear remodeler concentrations cellular response times for repositioning a given nucleosome were calculated to be in the range of tens of seconds to minutes.
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Project description:Chromatin dynamics play a central role in maintaining genome integrity, but how this is achieved remains largely unknown. Here, we report that microrchidia CW-type zinc finger 2 (MORC2), an uncharacterized protein with a derived PHD finger domain and a conserved GHKL-type ATPase module, is a physiological substrate of p21-activated kinase 1 (PAK1), an important integrator of extracellular signals and nuclear processes. Following DNA damage, MORC2 is phosphorylated on serine 739 in a PAK1-dependent manner, and phosphorylated MORC2 regulates its DNA-dependent ATPase activity to facilitate chromatin remodeling. Moreover, MORC2 associates with chromatin and promotes gamma-H2AX induction in a PAK1 phosphorylation-dependent manner. Consequently, cells expressing MORC2-S739A mutation displayed a reduction in DNA repair efficiency and were hypersensitive to DNA-damaging agent. These findings suggest that the PAK1-MORC2 axis is critical for orchestrating the interplay between chromatin dynamics and the maintenance of genomic integrity through sequentially integrating multiple essential enzymatic processes.
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