Localization of a putative transcriptional regulator (ATRX) at pericentromeric heterochromatin and the short arms of acrocentric chromosomes

Abstract

ATRX is a member of the SNF2 family of helicase͞ATPases that is thought to regulate gene expression via an effect on chromatin structure and͞or function. Mutations in the hATRX gene cause severe syndromal mental retardation associated with ␣-thalassemia. Using indirect immunofluorescence and confocal microscopy we have shown that ATRX protein is associated with pericentromeric heterochromatin during interphase and mitosis. By coimmunofluorescence, ATRX localizes with a mouse homologue of the Drosophila heterochromatic protein HP1 in vivo, consistent with a previous two-hybrid screen identifying this interaction. From the analysis of a trap assay for nuclear proteins, we have shown that the localization of ATRX to heterochromatin is encoded by its N-terminal region, which contains a conserved plant homeodomainlike finger and a coiled-coil domain. In addition to its association with heterochromatin, at metaphase ATRX clearly binds to the short arms of human acrocentric chromosomes, where the arrays of ribosomal DNA are located. The unexpected association of a putative transcriptional regulator with highly repetitive DNA provides a potential explanation for the variability in phenotype of patients with identical mutations in the ATRX gene.

The double face of the histone variant H3.3

“…ATRX localizes to pericentric heterochromatin in HeLa cells [68] and was previously shown to physically associate and form a complex with DAXX in vivo [69]. DAXX was recently shown to exhibit chaperone activity and directly interact with H3.3 in a tighter manner than with H3.1 in vitro [48].…”

Alpha-thalassemia/mental retardation syndrome, X-Linked (ATR-X, MIM #301040, ATR-X/XNP/XH2 gene MIM #300032)

“…The ATR-X protein is a nuclear protein found principally associated to the short arm of acrocentric chromosomes during mitosis 5 and tightly associated with the nuclear matrix at interphase; the differential localisation of the protein during the cell cycle could be regulated by phosphorylation. 6 Interactions between the murine Atrx protein and the heterochromatin protein HP1 was reported 7 and the human ATRX protein was shown to associate with another chromatin protein (EZH2) in yeast two-hybrid assays and in vitro.…”

ATRX induction by mutant huntingtin via Cdx2 modulates heterochromatin condensation and pathology in Huntington's disease

“…ATRX is localized to pericentromeric heterochromatin and can physically interact with proteins that reside within heterochromatin including HP1. 19 The ATRX protein also localizes to PML-NBs that may have a role in transcription regulation during the neurodegenerative process. 20 To address how ATRX contributes to PML-NB formation and chromatin remodeling, we overexpressed GFP-ATRX fusion protein in striatal cells and measured PML-NB and H3K9me3 immunoreactivities and levels.…”

“…These results suggest that heterochromatin remodeling in striatal cells is driven by ATRX under neurodegenerative conditions. 19 Interestingly, both the N-terminal ATRX-Dnmt3-Dnmt3L (ADD) domain and the C-terminal ATPase/helicase domain of ATRX modulated the dynamics of pericentromeric heterochromatin by increasing H3K9me3 levels at its target loci and ultimately, to nuclear damage in striatal cells. 15 These findings suggest that ATRX facilitates the pathological heterochromatin condensation and triggers the cascade of events leading to neuronal degeneration.…”