XNP/dATRX interacts with DREF in the chromatin to regulate gene expression

Autor: Martha Vázquez, Akihito Kawamori, Viviana Valadez-Graham, Yasuhide Yoshioka, Masamitsu Yamaguchi, Oscar Velazquez, Adina Neumann, Mario Zurita
Rok vydání: 2011
Předmět:
Zdroj: Nucleic Acids Research
ISSN: 1362-4962
0305-1048
Popis: The human Alpha-Thalassemia and mental Retardation X-linked syndrome (hATRX) gene encodes a chromatin remodeling protein that contains several conserved motifs. The ATRX protein has a helicase/ATPase domain of the SWI/SNF family at its carboxyl terminus, and this domain is characteristic of the catalytic subunits of chromatin remodeling complexes (1). At its amino terminus, the ATRX protein has a domain composed of a Plant Homeo Domain (PHD) and a GATA-like zinc-finger motif, known as the ATRX-DNMT3A-DNMT3L (ADD) domain because this configuration of Zinc fingers has been found in the DNA-methyl-transferases DNMT3A and DNMT3L (2). The ADD domain of the DNMT3A and DNMT3L proteins has been shown to bind histone tails (3). This interaction has been proposed to mediate the recruitment of these proteins to chromatin (4). The ADD domain of hATRX is very similar to the one present in the DNMTs and recently has been reported to bind H3 when its K4, and K9 residues are methylated (5–7). Mutations in hATRX are associated with several syndromes linked to the X chromosome. For this reason, most of the patients affected are males. Patients with mutations in hATRX have developmental defects in the urogenital system, suffer severe dysfunctions in the central nervous system, suffer from α-thalassemia, have impaired motor abilities, and display a characteristic facial dysmorphism. About 50% of the mutations detected in patients afflicted with ATRX syndrome are located in the ADD region, and ∼30% are in the SNF2 domain (1). Some of the phenotypes observed in patients carrying ATRX mutations may be due to the role of ATRX in the regulation of transcription. As a result, different molecular studies have focused on elucidating the role played by ATRX in transcription (8,9). A recent genome-wide analysis of human and mouse cells demonstrates that ATRX can bind G-rich tandem repeat sequences. Importantly, genes associated with these tandem repeat sequences are deregulated when ATRX is mutated (10). Furthermore, the same study shows that ATRX can directly bind to G-rich sequences that may form G quadruplex structures (10). In addition, mammalian ATRX is capable of interacting with other cellular factors including Heterochromatin Protein 1 (HP1), Methyl-CpG-binding protein (MeCP2), cohesin, CCCTC-binding factor (CTCF) and the Death Associated Protein-6 (DAXX) presumably acting together as a H3.3 chaperone (11–15). The interaction of ATRX with CTCF and MeCP2 results in the repression of imprinted gene expression in the postnatal mouse (15). In addition, evidence suggests that in mice, the PAR genes are positively regulated by ATRX (16). In fact, expression of the α-globin genes is affected when ATRX is mutated, and this effect is determined by the number of the tandem G-rich repeats sequences upstream of this gene, suggesting that the ATRX mechanisms that influence gene expression are complex (10). Indeed, it is not clear if all the cases involve a direct interaction with chromatin or if this activity is mediated by an interaction with other undescribed factors. Therefore, the mechanism by which ATRX regulates gene expression is currently unknown. In Drosophila, XNP/ATRX is present as two isoforms (dATRXS and dATRXL) that are derived from the use of two alternative translational start codons (17). While some reports suggest that XNP/dATRXL interacts with HP1 in heterochromatic regions, including the chromocenter, other studies show evidence that dATRXL can also be located in euchromatin (18,19). The dATRXS isoform has also been shown to be distributed in different regions across polytene chromosomes (19). In Drosophila, XNP/dATRX mutants act as suppressors of position effect variegation (18,19). Therefore, it is likely that XNP/dATRX is a chromatin-associated protein in the fly. However, although both XNP/dATRX isoforms conserve the ATPase/helicase domain, they lack the human ADD domain, suggesting that these proteins participate in the control of gene expression through protein–protein interactions with other cell factors that may have DNA or chromatin binding domains. To test this hypothesis and to find putative XNP/dATRX partners, we used XNP/dATRX as a bait to screen an embryonic cDNA library through a yeast two-hybrid analysis, We identified, among several factors, that the transcription factor DREF interacts in vitro and in vivo with dATRX. DREF recognizes the consensus DNA element 5′-TATCGATA-3, which is highly prevalent in core promoters and is known as the DNA replication-related element (DRE) (20). In Drosophila, DREF regulates the expression of several genes that are required during the S phase of the cell cycle, such as PCNA, E2F and DNApol-α (22–24). Physically, DREF interacts with factors involved in chromatin structure and dynamics (25,26), and the wide spectrum of genes regulated by DREF suggests that this transcription factor acts in conjunction with a diverse array of transcriptional regulators. The interaction between XNP/dATRX and DREF results in the regulation of pannier (pnr) gene transcription. Mechanistically, we found that DREF binds to DRE elements present in the pnr promoter, where it works to maintain correct levels of pnr gene expression. The interaction of XNP/dATRX with DREF results in the repression of pnr transcription. These results suggest a dynamic interaction between XNP/dATRX and DREF to control the expression of a factor that is required for various biological processes during the development of Drosophila.
Databáze: OpenAIRE
Externí odkaz: