Structural basis for PHDVC5HCHNSD1-C2HRNizp1 interaction: implications for Sotos syndrome

A novel nonsense variant in NSD1 gene in a female child with Sotos syndrome: A case report and literature review

INTRODUCTION

Sotos syndrome (SS) is an overgrowth disease characterized by distinctive facial features, advanced bone age, macrocephaly, and developmental delay is associated with alterations in the NSD1 gene. Here, we report a case of a 4-year-old female child with SS caused by NSD1 gene nonsense mutation.

METHODS

Whole-exome sequencing (WES) was applied for probands and her parents. Sanger sequencing was used to confirm the mutation. We performed the literature review using PubMed and found 12 articles and 14 patients who presented with SS.

RESULTS

The patient showed typical facial features of SS, hand deformities, and seizure. WES revealed de novo heterozygous variant: NSD1 (NM_022455.5), c.6095G > A, p.TRP2032*. We also reviewed the phenotype spectrum of 14 patients with SS, who exhibited a variety of clinical phenotypes, including developmental delay, seizures, scoliosis, hearing loss, cardiac and urinary system abnormalities, and so on.

DISCUSSION

The lack of correlation between mutation sites or types and phenotypes was summarized by literature reviewing. The NSD1 protein contains 14 functional domains and this nonsense mutation was located in SET domain. Early appearance of the termination codon leads to protein truncation. Haploinsufficiency of the NSD1 gene causes the overgrowth disorders.

Insights into RAG Evolution from the Identification of "Missing Link" Family A RAGL Transposons

A series of "molecular domestication" events are thought to have converted an invertebrate RAG-like (RAGL) transposase into the RAG1-RAG2 (RAG) recombinase, a critical enzyme for adaptive immunity in jawed vertebrates. The timing and order of these events are not well understood, in part because of a dearth of information regarding the invertebrate RAGL-A transposon family. In contrast to the abundant and divergent RAGL-B transposon family, RAGL-A most closely resembles RAG and is represented by a single orphan RAG1-like (RAG1L) gene in the genome of the hemichordate Ptychodera flava (PflRAG1L-A). Here, we provide evidence for the existence of complete RAGL-A transposons in the genomes of P. flava and several echinoderms. The predicted RAG1L-A and RAG2L-A proteins encoded by these transposons intermingle sequence features of jawed vertebrate RAG and RAGL-B transposases, leading to a prediction of DNA binding, catalytic, and transposition activities that are a hybrid of RAG and RAGL-B. Similarly, the terminal inverted repeats (TIRs) of the RAGL-A transposons combine features of both RAGL-B transposon TIRs and RAG recombination signal sequences. Unlike all previously described RAG2L proteins, RAG2L-A proteins contain an acidic hinge region, which we demonstrate is capable of efficiently inhibiting RAG-mediated transposition. Our findings provide evidence for a critical intermediate in RAG evolution and argue that certain adaptations thought to be specific to jawed vertebrates (e.g. the RAG2 acidic hinge) actually arose in invertebrates, thereby focusing attention on other adaptations as the pivotal steps in the completion of RAG domestication in jawed vertebrates.

Insights into RAG evolution from the identification of "missing link" family A RAGL transposons

A series of "molecular domestication" events are thought to have converted an invertebrate RAG-like (RAGL) transposase into the RAG1-RAG2 (RAG) recombinase, a critical enzyme for adaptive immunity in jawed vertebrates. The timing and order of these events is not well understood, in part because of a dearth of information regarding the invertebrate RAGL-A transposon family. In contrast to the abundant and divergent RAGL-B transposon family, RAGL-A most closely resembles RAG and is represented by a single orphan RAG1-like (RAG1L) gene in the genome of the hemichordate Ptychodera flava (PflRAG1L-A). Here, we provide evidence for the existence of complete RAGL-A transposons in the genomes of P. flava and several echinoderms. The predicted RAG1L-A and RAG2L-A proteins encoded by these transposons intermingle sequence features of jawed vertebrate RAG and RAGL-B transposases, leading to a prediction of DNA binding, catalytic, and transposition activities that are a hybrid of RAG and RAGL-B. Similarly, the terminal inverted repeats (TIRs) of the RAGL-A transposons combine features of both RAGL-B transposon TIRs and RAG recombination signal sequences. Unlike all previously described RAG2L proteins, PflRAG2L-A and echinoderm RAG2L-A contain an acidic hinge region, which we demonstrate is capable of efficiently inhibiting RAG-mediated transposition. Our findings provide evidence for a critical intermediate in RAG evolution and argue that certain adaptations thought to be specific to jawed vertebrates (e.g., the RAG2 acidic hinge) actually arose in invertebrates, thereby focusing attention on other adaptations as the pivotal steps in the completion of RAG domestication in jawed vertebrates.

Chromatin regulation of transcriptional enhancers and cell fate by the Sotos syndrome gene NSD1

Nuclear receptor-binding SET-domain protein 1 (NSD1), a methyltransferase that catalyzes H3K36me2, is essential for mammalian development and is frequently dysregulated in diseases, including Sotos syndrome. Despite the impacts of H3K36me2 on H3K27me3 and DNA methylation, the direct role of NSD1 in transcriptional regulation remains largely unknown. Here, we show that NSD1 and H3K36me2 are enriched at cis-regulatory elements, particularly enhancers. NSD1 enhancer association is conferred by a tandem quadruple PHD (qPHD)-PWWP module, which recognizes p300-catalyzed H3K18ac. By combining acute NSD1 depletion with time-resolved epigenomic and nascent transcriptomic analyses, we demonstrate that NSD1 promotes enhancer-dependent gene transcription by facilitating RNA polymerase II (RNA Pol II) pause release. Notably, NSD1 can act as a transcriptional coactivator independent of its catalytic activity. Moreover, NSD1 enables the activation of developmental transcriptional programs associated with Sotos syndrome pathophysiology and controls embryonic stem cell (ESC) multilineage differentiation. Collectively, we have identified NSD1 as an enhancer-acting transcriptional coactivator that contributes to cell fate transition and Sotos syndrome development.

Non-histone binding functions of PHD fingers

Plant homeodomain (PHD) fingers comprise a large and well-established family of epigenetic readers that recognize histone H3. A typical PHD finger binds to the unmodified or methylated amino-terminal tail of H3. This interaction is highly specific and can be regulated by post-translational modifications (PTMs) in H3 and other domains present in the protein. However, a set of PHD fingers has recently been shown to bind non-histone proteins, H3 mimetics, and DNA. In this review, we highlight the molecular mechanisms by which PHD fingers interact with ligands other than the amino terminus of H3 and discuss similarities and differences in engagement with histone and non-histone binding partners.

Nizp1 is a specific NUP98 ‐ NSD1 functional interactor that regulates NUP98 ‐ NSD1 ‐dependent oncogenic programs

NSD1, NSD2 and NSD3 proteins constitute a family of histone 3 lysine 36 (H3K36) methyltransferases with similar domain architecture, but diversified activities, in part, dependent on their non-enzymatic domains. These domains, despite their high sequence identity, recruit the hosting proteins to different chromatin regions through the recognition of diverse epigenetic marks and/or associations to distinct interactors. In this sense, the PHDvC5HCH finger tandem domain represents a paradigmatic example of functional divergence within the NSD family. In this work, we prove and give a structural rationale for the uniqueness of the PHDvC5HCH domain of NSD1 in recognizing the C2HR Zinc finger domain of Nizp1 (NSD1 interacting Zn finger protein). Importantly, we show that, in a leukaemogenic context, Nizp1 is pivotal in driving the unscheduled expression of HoxA genes and of genes involved in the type I IFN pathway, triggered by the expression of the fusion protein NUP98-NSD1. These data provide the first insight into the pathophysiological relevance of the Nizp1-NSD1 functional association. Targeting of this interaction might open new therapeutic windows to inhibit the NUP98-NSD1 oncogenic properties.

Structural Bioinformatics and Deep Learning of Metalloproteins: Recent Advances and Applications

All living organisms require metal ions for their energy production and metabolic and biosynthetic processes. Within cells, the metal ions involved in the formation of adducts interact with metabolites and macromolecules (proteins and nucleic acids). The proteins that require binding to one or more metal ions in order to be able to carry out their physiological function are called metalloproteins. About one third of all protein structures in the Protein Data Bank involve metalloproteins. Over the past few years there has been tremendous progress in the number of computational tools and techniques making use of 3D structural information to support the investigation of metalloproteins. This trend has been boosted by the successful applications of neural networks and machine/deep learning approaches in molecular and structural biology at large. In this review, we discuss recent advances in the development and availability of resources dealing with metalloproteins from a structure-based perspective. We start by addressing tools for the prediction of metal-binding sites (MBSs) using structural information on apo-proteins. Then, we provide an overview of the methods for and lessons learned from the structural comparison of MBSs in a fold-independent manner. We then move to describing databases of metalloprotein/MBS structures. Finally, we summarizing recent ML/DL applications enhancing the functional interpretation of metalloprotein structures.

Role of NSD1 as potential therapeutic target in tumor

Nuclear receptor binding SET Domain Protein 1 (NSD1) is a bifunctional transcriptional regulatory protein that encodes histone methyltransferase. Mono- and di-methylation of H3K36 by NSD1 is mainly primarily involved in the regulation of gene expression, DNA repair, alternative splicing, and other important biological processes. Many types of cancers, including acute myelogenous leukemia (AML), liver cancer, lung cancer, endometrial carcinoma, colorectal cancer, and pancreatic cancer, are associated with NSD1 fusion, missense mutation, nonsense mutation, silent mutation, deletion, and insertion of frameshift, and deletion in a frame. Therefore, targeting NSD1 may be a potential strategy for tumor therapy. An in-depth study of the structure and biological activities of NSD1 sets the groundwork for improving tumor therapy and creating NSD1 inhibitors. This article emphasizes the role of NSD1 in tumorigenesis and the development of NSD1 targeted small-molecule inhibitors.

Structure, Activity and Function of the NSD3 Protein Lysine Methyltransferase

NSD3 is one of six H3K36-specific lysine methyltransferases in metazoans, and the methylation of H3K36 is associated with active transcription. NSD3 is a member of the nuclear receptor-binding SET domain (NSD) family of histone methyltransferases together with NSD1 and NSD2, which generate mono- and dimethylated lysine on histone H3. NSD3 is mutated and hyperactive in some human cancers, but the biochemical mechanisms underlying such dysregulation are barely understood. In this review, the current knowledge of NSD3 is systematically reviewed. Finally, the molecular and functional characteristics of NSD3 in different tumor types according to the current research are summarized.

In silico derived small molecules targeting the finger-finger interaction between the histone lysine methyltransferase NSD1 and Nizp1 repressor

PHD fingers are small chromatin binding domains, that alone or in tandem work as versatile interaction platforms for diversified activities, ranging from the decoding of the modification status of histone tails to the specific recognition of non-histone proteins. They play a crucial role in their host protein as mutations thereof cause several human malignancies. Thus, PHD fingers are starting to be considered as valuable pharmacological targets. While inhibitors or chemical probes of the histone binding activity of PHD fingers are emerging, their druggability as non-histone interaction platform is still unexplored. In the current study, using a computational and experimental pipeline, we provide proof of concept that the tandem PHD finger of Nuclear receptor-binding SET (Su(var)3–9, Enhancer of zeste, Trithorax) domain protein 1 (PHD_VC5HCH_NSD1) is ligandable. Combining virtual screening of a small subset of the ZINC database (Zinc Drug Database, ZDD, 2924 molecules) to NMR binding assays and ITC measurements, we have identified Mitoxantrone dihydrochloride, Quinacrine dihydrochloride and Chloroquine diphosphate as the first molecules able to bind to PHD_VC5HCH_NSD1 and to reduce its documented interaction with the Zinc finger domain (C2HR_Nizp1) of the transcriptional repressor Nizp1 (NSD1-interacting Zn-finger protein). These results pave the way for the design of small molecules with improved effectiveness in inhibiting this finger-finger interaction.

The Role of Nuclear Receptor-Binding SET Domain Family Histone Lysine Methyltransferases in Cancer

The nuclear receptor-binding SET Domain (NSD) family of histone H3 lysine 36 methyltransferases is comprised of NSD1, NSD2 (MMSET/WHSC1), and NSD3 (WHSC1L1). These enzymes recognize and catalyze methylation of histone lysine marks to regulate chromatin integrity and gene expression. The growing number of reports demonstrating that alterations or translocations of these genes fundamentally affect cell growth and differentiation leading to developmental defects illustrates the importance of this family. In addition, overexpression, gain of function somatic mutations, and translocations of NSDs are associated with human cancer and can trigger cellular transformation in model systems. Here we review the functions of NSD family members and the accumulating evidence that these proteins play key roles in tumorigenesis. Because epigenetic therapy is an important emerging anticancer strategy, understanding the function of NSD family members may lead to the development of novel therapies.