DNA methylation is an important epigenetic modification that is essential for various developmental processes through regulating gene expression, genomic imprinting, and epigenetic inheritance. Mammalian genomic DNA methylation is established during embryogenesis by de novo DNA methyltransferases, DNMT3A and DNMT3B, and the methylation patterns vary with developmental stages and cell types. DNA methyltransferase 3-like protein (DNMT3L) is a catalytically inactive paralogue of DNMT3 enzymes, which stimulates the enzymatic activity of Dnmt3a. Recent studies have established a connection between DNA methylation and histone modifications, and revealed a histone-guided mechanism for the establishment of DNA methylation. The ATRX-DNMT3-DNMT3L (ADD) domain of Dnmt3a recognizes unmethylated histone H3 (H3K4me0). The histone H3 tail stimulates the enzymatic activity of Dnmt3a in vitro, whereas the molecular mechanism remains elusive. Here we show that DNMT3A exists in an autoinhibitory form and that the histone H3 tail stimulates its activity in a DNMT3L-independent manner. We determine the crystal structures of DNMT3A-DNMT3L (autoinhibitory form) and DNMT3A-DNMT3L-H3 (active form) complexes at 3.82 and 2.90 Å resolution, respectively. Structural and biochemical analyses indicate that the ADD domain of DNMT3A interacts with and inhibits enzymatic activity of the catalytic domain (CD) through blocking its DNA-binding affinity. Histone H3 (but not H3K4me3) disrupts ADD-CD interaction, induces a large movement of the ADD domain, and thus releases the autoinhibition of DNMT3A. The finding adds another layer of regulation of DNA methylation to ensure that the enzyme is mainly activated at proper targeting loci when unmethylated H3K4 is present, and strongly supports a negative correlation between H3K4me3 and DNA methylation across the mammalian genome. Our study provides a new insight into an unexpected autoinhibition and histone H3-induced activation of the de novo DNA methyltransferase after its initial genomic positioning.

UHRF1 (Ubiquitin-like, with PHD and RING finger domains 1) plays an important role in DNA CpG methylation, heterochromatin function and gene expression. Overexpression of UHRF1 has been suggested to contribute to tumorigenesis. However, regulation of UHRF1 is largely unknown. Here we show that the deubiquitylase USP7 interacts with UHRF1. Using interaction-defective and catalytic mutants of USP7 for complementation experiments, we demonstrate that both physical interaction and catalytic activity of USP7 are necessary for UHRF1 ubiquitylation and stability regulation. Mass spectrometry analysis identified phosphorylation of serine (S) 652 within the USP7-interacting domain of UHRF1, which was further confirmed by a UHRF1 S652 phosphor (S652ph)-specific antibody. Importantly, the S652ph antibody identifies phosphorylated UHRF1 in mitotic cells and consistently S652 can be phosphorylated by the M phase-specific kinase CDK1-cyclin B in vitro. UHRF1 S652 phosphorylation significantly reduces UHRF1 interaction with USP7 in vitro and in vivo, which is correlated with a decreased UHRF1 stability in the M phase of the cell cycle. In contrast, UHRF1 carrying the S652A mutation, which renders UHRF1 resistant to phosphorylation at S652, is more stable. Importantly, cells carrying the S652A mutant grow more slowly suggesting that maintaining an appropriate level of UHRF1 is important for cell proliferation regulation. Taken together, our findings uncovered a cell cycle-specific signaling event that relieves UHRF1 from its interaction with USP7, thus exposing UHRF1 to proteasome-mediated degradation. These findings identify a molecular mechanism by which cellular UHRF1 level is regulated, which may impact cell proliferation.deubiquitination | phosphorylation UHRF1 S652 E pigenetic regulation has emerged as an important mechanism that regulates many chromatin template-based processes, including transcription, DNA replication, and repair. An important component of epigenetic regulation is DNA CpG methylation, which is mediated by DNA methyltransferases such as DMNT1 and DNMT3a/b and an accessory factor DNMT3L (1, 2). Recent studies demonstrate that maintenance of DNA methylation patterns requires UHRF1 (Ubiquitin-like, with PHD and RING finger domains 1) (also called Np95 and ICBP90). UHRF1 binds hemimethylated CpG and recruits DNMT1 to ensure faithful propagation of the DNA methylation patterns through DNA replication (3, 4). UHRF1 is also localized to euchromatic regions where it regulates transcription possibly by impacting DNA methylation and histone modifications (5, 6). UHRF1 has been shown to regulate cell proliferation, and its loss has been implicated in the mis-regulation of both G1 and G2/M phases of the cell cycle, respectively (7). However, very little is known how this important epigenetic regulator itself is regulated. To address this question, we have recently undertaken a proteomics approach and identified a cell cycle signaling-regulated physical interaction of UHRF1 with the deubiquitylase USP7 (HAUSP) (8,9) ...

Phyllodes tumors of the breast are rare tumor types that consist of 0.3-1.0% in all breast tumors. The naming and classification of breast phyllodes tumor have been debated for years. Based on the classification criteria modified by WHO in 2003, this review mainly introduced the clinicopathologic characteristics, pre-operational diagnosis and the treatment of breast phyllodes tumors, and also summarized the prognostic factors related to tumor recurrence.

Spectroscopy in the wavelength region of 330 nm to 400 nm for highly charged tungsten was performed using the High Temperature Super Conducting Electron Beam Ion Trap (SH-HtscEBIT) at Fudan University. Three lines from palladium-like tungsten (W 28+ ) were identified as transitions between metastable levels in the first excited configuration ([Kr]4d 9 4f). A secondorder relativistic many-body perturbation theory approach and a simple collisional radiative model were used to theoretically study the fine structure levels of the 4d 9 4f configuration. The calculated results show qualitative agreement with experiment. We conclude that some levels in the 4d 9 4f excited configuration have extremely long lifetimes and may exhibit extraordinarily high populations, possibly leading to indirect ionization in, for example, fusion plasmas.

No abstract