UHRF1 is a multidomain protein crucially linking histone H3 modification states and DNA methylation. While the interaction properties of its specific domains are well characterized, little is known about the regulation of these functionalities. We show that UHRF1 exists in distinct active states, binding either unmodified H3 or the H3 lysine 9 trimethylation (H3K9me3) modification. A polybasic region (PBR) in the C terminus blocks interaction of a tandem tudor domain (TTD) with H3K9me3 by occupying an essential peptide-binding groove. In this state the plant homeodomain (PHD) mediates interaction with the extreme N terminus of the unmodified H3 tail. Binding of the phosphatidylinositol phosphate PI5P to the PBR of UHRF1 results in a conformational rearrangement of the domains, allowing the TTD to bind H3K9me3. Our results define an allosteric mechanism controlling heterochromatin association of an essential regulatory protein of epigenetic states and identify a functional role for enigmatic nuclear phosphatidylinositol phosphates.

The bromodomain and extraterminal (BET) subfamily of bromodomain-containing proteins has emerged in the last few years as an exciting, novel target group. BRD4, the best studied BET protein, is implicated in a number of hematological and solid tumors. This is linked to its role in modulating transcription elongation of essential genes involved in cell cycle and apoptosis such as c-Myc and BCL2. Potent BET inhibitors with promising antitumor efficacy in a number of preclinical cancer models have been identified in recent years. This led to clinical studies focusing mostly on the treatment of leukemia and lymphoma, and first encouraging signs of efficacy have already been reported. Here we discuss the biology of BRD4, its known interaction partners and implication in different tumor types. Further, we summarize the current knowledge on BET bromodomain inhibitors.

Over 60 bromodomains belonging to proteins with very different functions have been identified in humans. Several of them interact with acetylated lysine residues, leading to the recruitment and stabilization of protein complexes. The bromodomain and extra-terminal domain (BET) proteins contain tandem bromodomains which bind to acetylated histones and are thereby implicated in a number of DNA-centered processes, including the regulation of gene expression. The recent identification of inhibitors of BET and non-BET bromodomains is one of the few examples in which effective blockade of a protein-protein interaction can be achieved with a small molecule. This has led to major strides in the understanding of the function of bromodomain-containing proteins and their involvement in diseases such as cancer and inflammation. Indeed, BET bromodomain inhibitors are now being clinically evaluated for the treatment of hematological tumors and have also been tested in clinical trials for the relatively rare BRD-NUT midline carcinoma. This review gives an overview of the newest developments in the field, with a focus on the biology of selected bromodomain proteins on the one hand, and on reported pharmacological inhibitors on the other, including recent examples from the patent literature.

Background: Chromatin-HP1 (heterochromatin protein 1) interaction is crucial for heterochromatin assembly. Results: hHP1␤ uses alternative interfaces to bind nucleosomes depending on histone 3 methylation within a highly dynamic complex. Conclusion: hHP1␤ explores chromatin for sites of methyl-mark enrichment where it can bind histone 3 tails from adjacent nucleosomes. Significance: We provide a conceptual framework to understand the molecular basis of dynamic interactions regulated by histone modification.

Chromosomes in eukaryotic cell nuclei are not uniformly organized, but rather contain distinct chromatin elements, with each state having a defined biochemical structure and biological function. These are recognizable by their distinct architectures and molecular components, which can change in response to cellular stimuli or metabolic requirements. Chromatin elements are characterized by the fundamental histone and DNA components, as well as other associated non-histone proteins and factors. Post-translational modifications of histone proteins in particular often correlate with a specific chromatin structure and function. Patterns of histone modifications are implicated as having a role in directing the level of chromatin compaction, as well as playing roles in multiple functional pathways directing the readout of distinct regions of the genome. We review the properties of various chromatin elements and the apparent links of histone modifications with chromatin organization and functional output.