Characterization of the ATP-Dependent Chromatin Remodeling Enzyme CHD8.

Abstract

Chromodomain Helicase DNA-binding protein 8 (CHD8) is an ATP-dependent chromatin remodeling enzyme that has been implicated in a variety of cellular processes from establishment of chromatin insulator elements to control of β-catenin and androgen receptor-responsive transcription. It is demonstrated here that CHD8 directly interacts with WDR5, RbBP5, and Ash2L both on an individual basis and in the context of the WDR5/RbBP5/Ash2L complex. CHD8 is localized to the promoters of the HOXA genes and is involved in the regulation of HOXA genes, specifically HOXA2. CHD8 is shown to be required for the proper recruitment of the WDR5/RbBP5/Ash2L complex to the HOXA2 promoter. CHD8 is also required for the proper establishment of histone methylation patterns at the HOXA2 locus upon activation of the gene. Additionally, the WDR5/RbBP5/Ash2L complex is demonstrated to be a histone H3 methyltransferase independently of the association with CHD8. Chromodomains are generally recognized to bind to methylated histone tails, although the specific methyl mark bound varies depending on the chromodomain-containing protein. The tandem chromodomains of CHD8 are demonstrated here to bind to the core of histone H3 and H4 in a manner independent of methylation status. Each individual chromodomain of CHD8 also shows this same binding activity, discounting a cooperative fold mechanism seen in other CHD proteins. A mutant CHD8 construct lacking the N-terminus, including the chromodomains, loses nucleosome remodeling capabilities but displays enhanced ATPase activity, pointing towards a role for the chromodomains in the regulation of CHD8 enzymatic activity. Initial studies have been performed on a second Snf2 domain-containing protein, helicase-like transcription factor (HLTF), which is related to the yeast DNA repair protein Rad5. This work has provided insight into the methylation status of the HLTF promoter in several cell lines. HLTF has been found in a complex approximately 150 kDa in size, which is likely indicative of HLTF existing primarily as a monomer. Finally, HLTF appeared not to function as an ATP dependent nucleosome remodeling enzyme, providing evidence for HLTF involvement in an alternative cellular pathway, likely DNA repair.