Histone H1x is highly expressed in human neuroendocrine cells and tumours

MEF2D facilitates liver metastasis of gastric cancer cells through directly inducing H1X under IL-13 stimulation

Liver metastasis is the most common metastatic occurrence in gastric cancer patients, although the precise mechanism behind it remains unclear. Through a combination of proteomics and quantitative RT-PCR, our study has revealed a significant correlation between the upregulation of myocyte enhancer factor-2D (MEF2D) and both distant metastasis and poor prognosis in gastric cancer patients. In mouse models, we observed that overexpressing or knocking down MEF2D in gastric cancer cells respectively promoted or inhibited liver metastasis. Furthermore, our research has demonstrated that MEF2D regulates the transcriptional activation of H1X by binding to the H1X promoter. This regulation leads to the upregulation of H1X, which, in turn, promotes the in vivo metastasis of gastric cancer cells along with the upregulation of the downstream gene β-CATENIN. Additionally, we found that the expression of MEF2D and H1X at both mRNA and protein levels can be induced by the inflammatory factor IL-13, and this induction exhibits a time gradient dependence. In human gastric cancer tissues, the expression of IL13RA1, the receptor for IL-13, positively correlates with the expression of MEF2D and H1X. IL13RA1 has been identified as an intermediate receptor through which IL-13 regulates MEF2D. In conclusion, our findings suggest that MEF2D plays a crucial role in promoting liver metastasis of gastric cancer by upregulating H1X and downstream target β-CATENIN in response to IL-13 stimulation. Targeting MEF2D could therefore be a promising therapeutic strategy for the clinical management of gastric cancer. STATEMENT OF SIGNIFICANCE: MEF2D promotes its transcriptional activation in gastric cancer cells by binding to the H1X promoter and is upregulated by IL-13-IL13RA1, thereby promoting distant metastasis of gastric cancer.

Indications for genetic study in gastro-entero-pancreatic and thoracic neuroendocrine tumors

Gastro-entero-pancreatic (GEP-NET) and thoracic neuroendocrine tumours (NETs) are one of the most heritable groups of neoplasms in the body, being multiple endocrine neoplasia syndrome type 1 (MEN1), the genetic syndrome most frequently associated with this type of tumours. Moreover, Von Hippel Lindau syndrome, tuberous sclerosis, type 4 multiple neoplasia syndrome, and type 1 neurofibromatosis are associated with an increased risk of developing GEP-NETs. Another important aspect in GEP-NETs and thoracic NETs is the knowledge of the molecular background since the molecular profile of these tumours may have implications in the prognosis and in the response to specific treatments. This review summarizes the main indications for performing a genetic study in patients with GEP-NETs and thoracic NETs, and the methods used to carry it out. Moreover, it offers a description of the main hereditary syndromes associated with these NETs and their molecular background, as well as the clinical implications of the molecular profile.

Epigenetic Regulation in Gastroenteropancreatic Neuroendocrine Tumors

Gastroenteropancreatic neuroendocrine neoplasms are a rare, diverse group of neuroendocrine tumors that form in the pancreatic and gastrointestinal tract, and often present with side effects due to hormone hypersecretion. The pathogenesis of these tumors is known to be linked to several genetic disorders, but sporadic tumors occur due to dysregulation of additional genes that regulate proliferation and metastasis, but also the epigenome. Epigenetic regulation in these tumors includes DNA methylation, chromatin remodeling and regulation by noncoding RNAs. Several large studies demonstrate the identification of epigenetic signatures that may serve as biomarkers, and others identify innovative, epigenetics-based targets that utilize both pharmacological and theranostic approaches towards the development of new treatment approaches.

Bronchial Carcinoids: From Molecular Background to Treatment Approach

Simple Summary

Bronchial carcinoids (BCs) are uncommon and usually slow growing neuroendocrine epithelial malignancies that represent less than 2% of all lung cancers. Differences in the extent of molecular alterations between neuroendocrine carcinomas and BCs may underline the differences in the aggressiveness of these lesions. Moreover, although atypical BCs and typical BCs have similar set of mutations, some differential molecular and genetic alterations have been described between these two entities. A better understanding of the genetic and molecular background of BCs would allow a better selection of medical treatments in these patients. Regarding treatment, most BCs can be cured by surgery; however, inoperable tumors are mostly insensitive to chemotherapy and radiotherapy. In advanced BCs, the only drug that has a positive phase III clinical trial in BCs is everolimus. Somatostatin analogues constitute the gold standard for symptomatic relief. Peptide receptor radionuclide therapy has been associated with longer progression free. The efficacy of other treatments such as antiangiogenic agents and immunotherapy is still not established.

Abstract

A better understanding of the genetic and molecular background of bronchial carcinoids (BCs) would allow a better estimation of the risk of disease progression and the personalization of treatment in cases of advanced disease. Molecular studies confirmed that lungs neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs) are different entities; thus, no progression of NET to NEC is expected. In BCs, MEN1 gene mutations and deletions and decreased gene expression have been associated with a poor prognosis. ATRX mutation has also been linked to a shorter disease-specific survival. In terms of therapeutic targets, PI3K/AKT/mTOR pathway mutations have been described in 13% of typical carcinoids (TCs) and 39% of atypical carcinoids (ACs), representing a targetable mutation with kinase inhibitors. Regarding treatment, surgical resection is usually curative in localized BCs and adjuvant treatment is not routinely recommended. Multiple options for systemic therapy exist for patients with advanced BCs, although limited by a heterogeneity in the scientific evidence behind their use recommendation. These options include somatostatin analogues, everolimus, peptide receptor radionuclide therapy, chemotherapy, radiotherapy, antiangiogenic agents, and immunotherapy. In this article, we provide a comprehensive review about the molecular and genetic background of BCs, and about the treatment of local and metastatic disease, as well as the main paraneoplastic syndromes that have been associated with this tumor.

Histone H1 Mutations in Lymphoma: A Link(er) between Chromatin Organization, Developmental Reprogramming, and Cancer

Aberrant cell fate decisions due to transcriptional misregulation are central to malignant transformation. Histones are the major constituents of chromatin, and mutations in histone-encoding genes are increasingly recognized as drivers of oncogenic transformation. Mutations in linker histone H1 genes were recently identified as drivers of peripheral lymphoid malignancy. Loss of H1 in germinal center B cells results in widespread chromatin decompaction, redistribution of core histone modifications, and reactivation of stem cell-specific transcriptional programs. This review explores how linker histones and mutations therein regulate chromatin structure, highlighting reciprocal relationships between epigenetic circuits, and discusses the emerging role of aberrant three-dimensional chromatin architecture in malignancy.

Exploring the Epigenome in Gastroenteropancreatic Neuroendocrine Neoplasias

Gastroenteropancreatic neuroendocrine neoplasias are a diverse group of neoplasms with different characteristics in terms of site, biological behaviour and metastatic potential. In comparison to other cancers, they are genetically quiet, harbouring relatively few somatic mutations. It is increasingly becoming evident that epigenetic changes are as relevant, if not more so, as somatic mutations in promoting oncogenesis. Despite significant tumour heterogeneity, it is obvious that DNA methylation, histone and chromatin modifications and microRNA expression profiles are distinctive for GEP-NEN subtypes and may correlate with clinical outcome. This review summarises existing knowledge on epigenetic changes, identifying potential contributions to pathogenesis and oncogenesis. In particular, we focus on epigenetic changes pertaining to well-differentiated neuroendocrine tumours, which make up the bulk of NENs. We also highlight both similarities and differences within the subtypes of GEP-NETs and how these relate and compare to other types of cancers. We relate epigenetic understanding to existing treatments and explore how this knowledge may be exploited in the development of novel treatment approaches, such as in theranostics and combining conventional treatment modalities. We consider potential barriers to epigenetic research in GEP-NENs and discuss strategies to optimise research and development of new therapies.

Tissue Proteome Signatures Associated with Five Grades of Prostate Cancer and Benign Prostatic Hyperplasia

The histology-based Gleason score (GS) of prostate cancer (PCa) tissue biopsy is the most accurate predictor of disease aggressiveness and an important measure to guide treatment strategies and patient management. The variability associated with PCa tumor sampling and the subjective determination of the GS are challenges that limit accurate diagnostication and prognostication. Thus, novel molecular signatures are needed to distinguish between indolent and aggressive forms of PCa for better patient management and outcomes. Herein, label-free LC-MS/MS proteomics is used to profile the proteome of 50 PCa tissues spanning five grade groups (n = 10 per group) relative to tissues from individuals with benign prostatic hyperplasia (BPH). Over 2000 proteins are identified albeit at different levels between and within the patient groups, revealing biological processes associated with specific grades. A panel of 11 prostate-derived proteins including IGKV3D-20, RNASET2, TACC2, ANXA7, LMOD1, PRCP, GYG1, NDUFV1, H1FX, APOBEC3C, and CTSZ display the potential to stratify patients from low and high PCa grade groups. Parallel reaction monitoring of the same sample cohort validate the differential expression of LMOD1, GYG1, IGKV3D-20, and RNASET2. The four proteins associated with low and high PCa grades reported here warrant further exploration as candidate biomarkers for PCa aggressiveness.

Comprehensive in vivo identification of the c-Myc mRNA protein interactome using HyPR-MS

Proteins bind mRNA through their entire life cycle from transcription to degradation. We analyzed c-Myc mRNA protein interactors in vivo using the HyPR-MS method to capture the crosslinked mRNA by hybridization and then analyzed the bound proteins using mass spectrometry proteomics. Using HyPR-MS, 229 c-Myc mRNA-binding proteins were identified, confirming previously proposed interactors, suggesting new interactors, and providing information related to the roles and pathways known to involve c-Myc. We performed structural and functional analysis of these proteins and validated our findings with a combination of RIP-qPCR experiments, in vitro results released in past studies, publicly available RIP- and eCLIP-seq data, and results from software tools for predicting RNA-protein interactions.

Genetics and Epigenetics of Gastroenteropancreatic Neuroendocrine Neoplasms

Gastroenteropancreatic (GEP) neuroendocrine neoplasms (NENs) are heterogeneous regarding site of origin, biological behavior, and malignant potential. There has been a rapid increase in data publication during the last 10 years, mainly driven by high-throughput studies on pancreatic and small intestinal neuroendocrine tumors (NETs). This review summarizes the present knowledge on genetic and epigenetic alterations. We integrated the available information from each compartment to give a pathway-based overview. This provided a summary of the critical alterations sustaining neoplastic cells. It also highlighted similarities and differences across anatomical locations and points that need further investigation. GEP-NENs include well-differentiated NETs and poorly differentiated neuroendocrine carcinomas (NECs). NENs are graded as G1, G2, or G3 based on mitotic count and/or Ki-67 labeling index, NECs are G3 by definition. The distinction between NETs and NECs is also linked to their genetic background, as TP53 and RB1 inactivation in NECs set them apart from NETs. A large number of genetic and epigenetic alterations have been reported. Recurrent changes have been traced back to a reduced number of core pathways, including DNA damage repair, cell cycle regulation, and phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling. In pancreatic tumors, chromatin remodeling/histone methylation and telomere alteration are also affected. However, also owing to the paucity of disease models, further research is necessary to fully integrate and functionalize data on deregulated pathways to recapitulate the large heterogeneity of behaviors displayed by these tumors. This is expected to impact diagnostics, prognostic stratification, and planning of personalized therapy.

Proteomic View of the Crosstalk between Lactobacillus mucosae and Intestinal Epithelial Cells in Co-culture Revealed by Q Exactive-Based Quantitative Proteomics

Lactobacilli are bacteria that are beneficial to host health, but information on communication between Lactobacilli and host cells in the intestine is lacking. In this study, we examined the proteomes of the Lactobacillus mucosae strain LM1, as a model of beneficial bacteria, and the intestinal porcine epithelial cell line (IPEC-J2) after co-culture. Label-free proteomics demonstrated the high-throughput capability of the technique, and robust characterization of the functional profiles and changes in the bacteria and intestinal cells was achieved in pure and mixed cultures. After co-culture, we identified totals of 376 and 653 differentially expressed proteins in the LM1 and IPEC-J2 proteomes, respectively. The major proteomic changes in the LM1 strain occurred in the functional categories of transcription, general function, and translation, whereas those in IPEC-J2 cells involved metabolic and cellular processes, and cellular component organization/biogenesis. Among them, elongation factor Tu, glyceraldehyde 3-phosphate dehydrogenase, and phosphocarrier protein HPr, which are known to be involved in bacterial adhesion, were upregulated in LM1. In contrast, proteins involved in tight junction assembly, actin organization, and genetic information processing (i.e., histones and signaling pathways) were significantly upregulated in IPEC-J2 cells. Furthermore, we identified functional pathways that are possibly involved in host–microbe crosstalk and response. These findings will provide novel insights into host–bacteria communication and the molecular mechanism of probiotic establishment in the intestine.

Temporally and Spatially Regulated Expression of the Linker Histone H1fx During Mouse Development

The linker histone H1fx is the least characterized member of the H1 family. To investigate the developmental changes of H1fx, we performed an immunohistochemical analysis of its expression pattern from embryos to adult mice. We found that H1fx was highly expressed during gastrulation, and was positive in all embryonic germ layers between E8.5 and E10.5, which mostly overlapped with the expression of the proliferation marker Ki-67. Neural and mesenchyme tissues strongly expressed H1fx at E10.5. H1fx expression began to be restricted at around E12.5. Western blot analysis of brain tissues demonstrated that the total expression level of H1fx gradually decreased with time from E12.5 to adulthood, whereas H1f0 was increased over this period. In adult mice, H1fx was restrictively expressed at the hypothalamus, subventricular zone, subgranular zone, medulla of the adrenal grand, islets of Langerhans, and myenteric plexus. Taken together, these data suggest that H1fx is preferentially expressed in immature embryonic cells and plays some roles in cells with neural properties.

Genetics and epigenetics in small intestinal neuroendocrine tumours

Neuroendocrine tumour of the small intestine (SI-NET), formerly known as midgut carcinoid tumour, is the most common small intestinal malignancy. The incidence is rising, with recent reports of 0.67 per 100 000 in the USA and 1.12 per 100 000 in Sweden. SI-NETs often present a challenge in terms of diagnosis and treatment, as patients often have widespread disease and are beyond cure by surgery. Somatostatin analogues provide the mainstay of medical treatment to control hormonal excess and increase the time to progression. Despite overall favourable prognosis (5-year overall survival of 65%), there is a need to find markers to identify both patients with worse outcome and new targets for therapy. Loss on chromosome 18 has been reported in 60-90% of SI-NETs, but mutated genes on this chromosome have failed detection. Recently, a putative tumour suppressor role has been suggested for TCEB3C occurring at 18q21 (encoding elongin A3), which may undergo epigenetic repression. CDKN1B has recently been revealed as the only recurrently mutated gene in SI-NETs but, with a frequency as low as 8%, its role as a driver in SI-NET development may be questioned. Integrated genomewide analysis including exome and whole-genome sequencing, gene expression, DNA methylation and copy number analysis has identified three novel molecular subtypes of SI-NET with differing clinical outcome. DNA methylation analysis has demonstrated that SI-NETs have significant epigenetic dysregulation in 70-80% of tumours. In this review, we focus on understanding of the genetic, epigenetic and molecular events that lead to development and progression of SI-NETs.

NETs: organ-related epigenetic derangements and potential clinical applications

High-throughput next-generation sequencing methods have recently provided a detailed picture of the genetic landscape of neuroendocrine tumors (NETs), revealing recurrent mutations of chromatin-remodeling genes and little-to-no pathogenetic role for oncogenes commonly mutated in cancer. Concurrently, multiple epigenetic modifications have been described across the whole spectrum of NETs, and their putative function as tumorigenic drivers has been envisaged. As result, it is still unclear whether or not NETs are epigenetically-driven, rather than genetically-induced malignancies. Although the NET epigenome profiling has led to the identification of molecularly-distinct tumor subsets, validation studies in larger cohorts of patients are needed to translate the use of NET epitypes in clinical practice. In the precision medicine era, recognition of subpopulations of patients more likely to respond to therapeutic agents is critical, and future studies testing epigenetic biomarkers are therefore awaited. Restoration of the aberrant chromatin remodeling machinery is an attractive approach for future treatment of cancer and in several hematological malignancies a few epigenetic agents have been already approved. Although clinical outcomes of epigenetic therapies in NETs have been disappointing so far, further clinical trials are required to investigate the efficacy of these drugs. In this context, given the immune-stimulating effects of epidrugs, combination therapies with immune checkpoint inhibitors should be tested. In this review, we provide an overview of the epigenetic changes in both hereditary and sporadic NETs of the gastroenteropancreatic and bronchial tract, focusing on their diagnostic, prognostic and therapeutic implications.

Epigenetic changes in gastroenteropancreatic neuroendocrine tumours

An understanding of epigenetic drivers of tumorigenesis has developed rapidly during the last years. The identification of these changes including DNA methylation and histone modifications in gastroenteropancreatic neuroendocrine tumours (GEP-NETs) is a step forward in trying to define underlying biologic processes in this heterogeneous disease. The reversible nature of these changes represents a potential therapeutic target. We present an overview of the current knowledge of epigenetic alterations related to GEP-NETs, focusing on the influence and impact these changes have on pathogenesis and prognosis. The potential role of demethylating agents in the management of this patient population is discussed.

Molecular genetic findings in small bowel neuroendocrine neoplasms: a review of the literature

Small bowel neuroendocrine neoplasms (SBNEN) are the most common small bowel tumor and have an increasing incidence. Despite many treatment options, therapeutic strategy remains a key clinical challenge due to the paucity of large-scale, randomized controlled trials. The heterogeneity of SBNEN coupled with a lack of detailed information about the tumor biology, impedes patient stratification into groups based on tumor phenotypes or treatment response. More detailed analysis of the genetic and epigenetic characteristics of SBNEN, will allow treatment to move toward a more personalized medicine approach through the identification of novel biomarkers and therapeutic targets, with the aim to increase survival.

Current Perspective on the Pathogenesis of Small Intestinal Neuroendocrine Tumors: Progress in Biomarkers and Molecular Events

<b><i>Background:</i></b> Neuroendocrine tumors of the gastrointestinal tract differ in their histopathologic and clinical presentation. Small intestinal neuroendocrine tumors (SI-NETs), representing only a small portion within gastrointestinal malignancies, are often associated with a delayed diagnosis due to their non-specific symptoms. The increased incidence of SI-NETs during the last decades demands earlier diagnosis and more effective treatment, which both rely on a better understanding on the underlying molecular mechanisms. <b><i>Summary:</i></b> The purpose of this review is to discuss the biomolecular changes responsible for the pathogenesis of SI-NETs, and potential biomarkers in the diagnostic and prognostic evaluation. <b>Key Message</b> A greater understanding of the molecular mechanisms that underpin the pathogenesis of small intestinal neuroendocrine tumors (SI-NETs) facilitates the classification, diagnosis and treatment of these relatively rare gastrointestinal malignancies. <b>Practical Implications</b> Currently, SI-NETs are diagnosed using histological examination and staining for various neuroendocrine markers. Genetically, SI-NETs are characterized by an absence of alterations to K-ras, p53 and DNA mismatch repair genes. Loss of chromosome 18, deletion of Smad2 and Smad4, and amplification of SRC, EGFR and PDGFR have been reported. Abnormal DNA methylation status, reflected by overexpression of DNA methyltransferase, higher methylation of the RASSF1A promoter and overexpression of histone H1x are also associated with SI-NETs. These tumors are also associated with fibrosis, possibly due to the high levels of serotonin and other fibrotic factors produced. Genetic studies have pinpointed genes that can differentiate SI-NETs from other neuroendocrine tumors (oxytocin receptor, G protein-coupled receptor 113, VMAT-1, CDX-2), enabling more accurate diagnosis. Paraneoplastic antigen Ma2, neurokinin A and the CART peptide are under investigation as prognostic biomarkers. There is, however, still an unmet need for more sensitive biomarkers for earlier diagnosis and for a more specific classification system that encompasses tumor histology and reliable predictors of clinical response.

Histone H1.0--a potential molecular marker with prognostic value for patients with malignant gliomas

BACKGROUND

Histones are proteins closely associated with the DNA molecules and serve as a structural scaffold for the organization of chromatin. They play an important role in the regulation of gene expression by changing the level of DNA compaction. The special subtype of the linker histone family-H1 zero (H1.0) is generally expressed in non-dividing, terminally differentiated cells. The aim of our study is to investigate the correlation between the quantities of histone H1.0 in human gliomas, the histopathological grade and the overall survival.

MATERIAL AND METHOD

Twenty-nine (N = 29) patients with intraaxial lesions underwent a microsurgical tumor resection. Tumor samples were snap-frozen in liquid nitrogen immediately after resection. Following a specific protocol, linker histones were extracted from the tumor specimens and the quantities of histone H1.0 were assessed. All patients were followed up prospectively.

RESULTS

Of the 29 patients in our study (M:F = 17:12), five had a grade II astrocytoma, seven had a grade III, and 17 had a grade IV, according to the World Health Organization (WHO) classification. At the end of the study, three patients were still alive. The mean quantities of H1.0 were: 23.3 for grade II tumors, 13.9 for grade III and 11.3 for grade IV tumors. The statistical analysis demonstrated that the histological grade, age and Karnofsky performance status (KPS) remain among the most reliable predictive factors for the survival of patients with gliomas. Grade III-IV gliomas had significantly less histone H1.0 than grade II gliomas. Conformably, in a multivariate Cox regression analysis, H1.0 made a small but significant contribution (p < 0.05) to survival rates.

CONCLUSION

Our study confirmed that histone H1.0 is a potential biological marker with prognostic value for the survival of patients with gliomas. The quantities of histone H1.0 are correlated to the histopathological grade of the tumor. The more aggressive and malignant gliomas tend to have lower quantities of histone H1.0.

Neuroendocrine tumours: cracking the epigenetic code

The field of epigenetics has evolved rapidly over recent years providing insight into the tumorigenesis of many solid and haematological malignancies. Determination of epigenetic modifications in neuroendocrine tumour (NET) development is imperative if we are to improve our understanding of the biology of this heterogenous group of tumours. Epigenetic marks such as DNA methylation at RASSF1A are frequent findings in NETs of all origins and may be associated with worse prognosis. MicroRNA signatures and histone modifications have been identified which can differentiate subtypes of NET and distinguish NET from adenocarcinoma in cases of diagnostic uncertainty. Historically, candidate gene-driven approaches have yielded limited insight into the epigenetics of NET. Recent progress has been facilitated by development of high-throughput tools including second-generation sequencing and arrays for analysis of the 'epigenome' of tumour and normal tissue, permitting unbiased approaches such as exome sequencing that identified mutations of chromatin-remodelling genes ATRX/DAXX in 44% of pancreatic NETs. Epigenetic changes are reversible and therefore represent an attractive therapeutic target; to date, clinical outcomes of epigenetic therapies in solid tumours have been disappointing; however, in vitro studies on NETs are promising and further clinical trials are required to determine utility of this class of novel agents. In this review, we perform a comprehensive evaluation of epigenetic changes found in NETs to date, including rare NETs such as phaeochromocytoma and adrenocortical tumours. We suggest priorities for future research and discuss potential clinical applications and novel therapies.

High-resolution mapping of h1 linker histone variants in embryonic stem cells

H1 linker histones facilitate higher-order chromatin folding and are essential for mammalian development. To achieve high-resolution mapping of H1 variants H1d and H1c in embryonic stem cells (ESCs), we have established a knock-in system and shown that the N-terminally tagged H1 proteins are functionally interchangeable to their endogenous counterparts in vivo. H1d and H1c are depleted from GC- and gene-rich regions and active promoters, inversely correlated with H3K4me3, but positively correlated with H3K9me3 and associated with characteristic sequence features. Surprisingly, both H1d and H1c are significantly enriched at major satellites, which display increased nucleosome spacing compared with bulk chromatin. While also depleted at active promoters and enriched at major satellites, overexpressed H1⁰ displays differential binding patterns in specific repetitive sequences compared with H1d and H1c. Depletion of H1c, H1d, and H1e causes pericentric chromocenter clustering and de-repression of major satellites. These results integrate the localization of an understudied type of chromatin proteins, namely the H1 variants, into the epigenome map of mouse ESCs, and we identify significant changes at pericentric heterochromatin upon depletion of this epigenetic mark.

Embryonic stem cells (ESCs) possess unique chromatin and epigenetic signatures, which are important in defining the identity and genome plasticity of pluripotent stem cells. Although ESC epigenomes have been extensively characterized, the genome localization of histone H1 variants, the chromatin structural proteins facilitating higher-order chromatin folding, remains elusive. Linker histone H1 is essential for mammalian development and regulates the expression of specific genes in ESCs. Here, by using a knock-in system coupled with ChIP–seq, we first achieve the high resolution mapping of two H1 variants on a genome-wide scale in mouse ESCs. Our study reveals the correlations of this underexplored histone family with other epigenetic marks and genome attributes. Surprisingly, we identify a dramatic enrichment of H1d and H1c at major satellite sequences. H1⁰, mapped using an overexpressing ESC line, shows similar features at active promoters but differential binding at repetitive sequences compared with H1d and H1c. Furthermore, using mutant ESCs that are deficient for multiple H1 variants, we demonstrate the role of H1 in chromocenter clustering and transcriptional repression of major satellites. Thus, these results connect this important repressive mark with the well understood ESC epigenome and identify novel functions of H1 in mammalian genome organization.

Profiling of linker histone variants in ovarian cancer

H1 linker histones play a key role in facilitating higher order chromatin folding. Emerging evidence suggests that H1 and its multiple variants are important epigenetic factors in modulating chromatin function and gene expression. Ovarian cancer is a devastating disease, ranking the fifth leading cause of all women cancer death due to its poor prognosis and difficulty in early diagnosis. Although epigenetic alterations in ovarian cancers are being appreciated in general, the role of H1 has not been explored. Here, using quantitative RT-PCR assays, we systematically examined the expression of 7 H1 genes in 33 human epithelial ovarian tumors. Whereas the expression of H1.3 was markedly increased, the expression of H10, H1.1, H1.4 and H1x were significantly reduced in malignant adenocarcinomas compared with benign adenomas. Strikingly, ovarian adenocarcinomas and adenomas exhibited characteristic expression patterns, and expression profiling of 7 H1 genes in tumor samples discriminated adenocarcinomas vs. adenomas with high accuracy. These findings indicate that the expression of H1 variants is exquisitely regulated and may serve as potential epigenetic biomarkers for ovarian cancer.

Small intestinal neuroendocrine cell pathobiology: 'carcinoid' tumors

PURPOSE OF REVIEW

Neuroendocrine tumors, particularly small intestinal tumors, also grouped as 'carcinoids', are defined by an increasing incidence and prevalence, a poor response to current therapies, and confusion regarding appropriate models for drug development. Despite these issues, approximately 350 studies were published in the last year.

RECENT FINDINGS

Two sources of confusion are clearly apparent. First, pharmacotherapeutic studies using pancreatic tumor cell lines as models for small intestinal or 'carcinoid' tumor biology are considered appropriate. Second, there is continued inclusion and analysis of pancreatic endocrine tumors with small intestinal neuroendocrine tumors in clinical studies. One highlight of this year is additional data confirming the significant differences between pancreatic tumor cell lines and small intestinal cell lines, the different gene expressions, for example, PAX8, between these two tumor types, and the observations that these two tumors respond differently in clinical trials, for example, to mammalian target of rapamycin (mTOR) inhibitors. Other highlights include delineating the role of the tumor microenvironment in the development of fibrosis and developing a minimum pathology dataset and a prognostic nomogram that may have utility in stratifying patients for clinical studies.

SUMMARY

A number of interesting studies have been published during 2009-2010, but critical areas remain that require resolution. Current data, for the most part, reflect amplification of previously held concepts with modest advances in novel information.