A Novel Transcription Regulatory Complex Containing Death Domain-associated Protein and the ATR-X Syndrome Protein

Abstract

Death domain-associated protein (Daxx) is a multifunctional protein that modulates both apoptosis and transcription. Within the nucleus, Daxx is a component of the promyelocytic leukemia protein (PML) nuclear bodies (NBs) and interacts with a number of transcription factors, yet its precise role in transcription remains elusive. To further define the function of Daxx, we have isolated its interacting proteins in the nucleus using epitope-tagged affinity purification and identified X-linked mental retardation and ␣-thalassaemia syndrome protein (ATRX), a putative member of the SNF2 family of ATP-dependent chromatin remodeling proteins that is mutated in several X-linked mental retardation disorders. We show that substantial amounts of endogenous Daxx and ATRX exist in a nuclear complex. Daxx binds to ATRX through its paired amphipathic alpha helices domains. ATRX has ATPase activity that is stimulated by mononucleosomes, and patient mutations in the ATPase domain attenuate this activity. ATRX strongly represses transcription when tethered to a promoter. Daxx does not affect the ATPase activity of ATRX, however, it alleviates its transcription repression activity. In addition, ATRX is found in the PML-NBs, and this localization is mediated by Daxx. These results show that the ATRX⅐Daxx complex is a novel ATP-dependent chromatin-remodeling complex, with ATRX being the core ATPase subunit and Daxx being the targeting subunit. Moreover, the localization of ATRX to the PML-NBs supports the notion that these structures may play an important role in transcription regulation.

Regulation of c-met expression by transcription repressor Daxx

“…In addition, Daxx forms a complex with protein ATRX and this complex displays chromatin-remodeling activity (Xue et al, 2003;Ishov et al, 2004;Tang et al, 2004). Besides chromatin remodeling, ATRX also possesses DNA methylation activity (Gibbons et al, 2000); DNA methylation is generally associated with repression of transcription (reviewed in Baylin and Ohm, 2006).…”

Patient mutations alter ATRX targeting to PML nuclear bodies

“…Baculovirus expressed ATRX protein containing engineered patient mutations within the SNF2 domain were shown to have attenuated ATPase activity compared to the wild-type (WT) protein. 15 Similarly, expression of the PHD domain in bacteria demonstrated that patient mutations impaired DNA-binding activity. 18 Collectively, these studies suggest that some mutations may interfere directly with function while others may have an indirect effect through altered protein stability or aberrant subnuclear targeting of the protein.…”

“…11 -14 The ATRX protein also localizes to PML-NBs where it interacts with Daxx, a transcriptional and apoptotic regulator. 12,15,16 ATRX is also involved in the regulation of methylation at ribosomal DNA (rDNA) repeats. 17 Given that ATRX acts at multiple locations within the nucleus, some mutations are likely to alter subnuclear localization thereby reducing function.…”

Histone Regulation in the CNS: Basic Principles of Epigenetic Plasticity

“…In addition to its interactions with MeCP2 and HP1, ATRX has also been shown to directly interact with the death-associated domain protein Daxx (Xue et al, 2003;Tang et al, 2004), which is known to have an important role in apoptotic signaling in a variety of cell types, including neurons (Raoul et al, 2002;Junn et al, 2005). ATRX and Daxx are known to co-localize to pericentromeric heterochromatin and at promyelocytic leukemia bodies in vivo (Xue et al, 2003), and ATRX/Daxx complex associations have been demonstrated to exhibit ATPase-dependent mononucleosomal remodeling activity (Tang et al, 2004). Nucleosomal dynamics, specifically histone deposition and eviction, are tightly regulated by the actions of specific chaperone proteins and via the enzymatic activity of ATPdependent remodelers.…”