Prevalence of clinically silent corticotroph macroadenomas.

OBJECTIVE: The prevalence of clinically silent corticotroph macroadenomas is unknown. Our aim was to determine the prevalence of clinically silent corticotroph macroadenomas among all pituitary macroadenomas. DESIGN: Patients scheduled to have transsphenoidal surgery for any sellar mass were prospectively evaluated clinically and biochemically. PATIENTS: Adults who were scheduled for transsphenoidal surgery for a sellar mass at a single academic medical centre. MEASUREMENTS: Patients were assessed clinically prior to surgery and graded as having typical, mild or no Cushingoid features. They were assessed biochemically by plasma ACTH and 24-h urine free cortisol (UFC). Excised tissue was examined histologically, and pituitary macroadenomas, examined by immunohistochemistry. Patients with corticotroph macroadenomas were classified as clinically silent if they exhibited no Cushingoid features but had elevated plasma ACTH and/or 24-h UFC. They were classified as totally silent if they exhibited neither Cushingoid features nor elevated plasma ACTH or 24-h UFC. RESULTS: Of 124 patients who had pathologically confirmed pituitary macroadenomas, 20 (16%) had corticotroph macroadenomas. Eight (40%) of these were clinically silent, in that they had no Cushingoid features but could be identified biochemically by elevated plasma ACTH (seven) and/or 24-h UFC (three). Five (25%) were totally silent. CONCLUSIONS: A substantial minority (16%) of pituitary macroadenomas treated surgically are corticotroph adenomas. Of these, 40% are clinically silent but can be recognized by elevated plasma ACTH and/or 24-h UFC. Recognizing these adenomas may influence the surgical approach and provide a marker by which to follow the response to treatment.

Histone acetyltransferase cofactor Trrap maintains self-renewal and restricts differentiation of embryonic stem cells.

Chromatin states are believed to play a key role in distinct patterns of gene expression essential for self-renewal and pluripotency of embryonic stem cells (ESCs); however, the genes governing the establishment and propagation of the chromatin signature characteristic of pluripotent cells are poorly understood. Here, we show that conditional deletion of the histone acetyltransferase cofactor Trrap in mouse ESCs triggers unscheduled differentiation associated with loss of histone acetylation, condensation of chromatin into distinct foci (heterochromatization), and uncoupling of H3K4 dimethylation and H3K27 trimethylation. Trrap loss results in downregulation of stemness master genes Nanog, Oct4, and Sox2 and marked upregulation of specific differentiation markers from the three germ layers. Chromatin immunoprecipitation-sequencing analysis of genome-wide binding revealed a significant overlap between Oct4 and Trrap binding in ESCs but not in differentiated mouse embryonic fibroblasts, further supporting a functional interaction between Trrap and Oct4 in the maintenance of stemness. Remarkably, failure to downregulate Trrap prevents differentiation of ESCs, suggesting that downregulation of Trrap may be a critical step guiding transcriptional reprogramming and differentiation of ESCs. These findings establish Trrap as a critical part of the mechanism that restricts differentiation and promotes the maintenance of key features of ESCs.

Histone acetyltransferase cofactor Trrap is essential for maintaining the hematopoietic stem/progenitor cell pool.

The pool of hematopoietic stem/progenitor cells, which provide life-long reconstitution of all hematopoietic lineages, is tightly controlled and regulated by self-renewal and apoptosis. Histone modifiers and chromatin states are believed to govern establishment, maintenance, and propagation of distinct patterns of gene expression in stem cells, however the underlying mechanism remains poorly understood. In this study, we identified a role for the histone acetytransferase cofactor Trrap in the maintenance of hematopietic stem/progenitor cells. Conditional deletion of the Trrap gene in mice resulted in ablation of bone marrow and increased lethality. This was due to the depletion of early hematopoietic progenitors, including hematopoietic stem cells, via a cell-autonomous mechanism. Analysis of purified bone marrow progenitors revealed that these defects are associated with induction of p53-independent apoptosis and deregulation of Myc transcription factors. Together, this study has identified a critical role for Trrap in the mechanism that maintains hematopoietic stem cells and hematopoietic system, and underscores the importance of Trrap and histone modifications in tissue homeostasis.

Treating Syrian refugees with diabetes and hypertension in Shatila refugee camp, Lebanon: Médecins Sans Frontières model of care and treatment outcomes.

BACKGROUND: Médecins Sans Frontières (MSF) has been providing primary care for non-communicable diseases (NCDs), which have been increasing in low to middle-income countries, in the Shatila refugee camp, Beirut, Lebanon, using a comprehensive model of care to respond to the unmet needs of Syrian refugees. The objectives of this study were to: 1) describe the model of care used and the Syrian refugee population affected by diabetes mellitus (DM) and/or hypertension (HTN) who had ≥ one visit in the MSF NCD clinic in Shatila in 2017, and 2) assess 6 month treatment outcomes. METHODS: A descriptive retrospective cohort study using routinely collected program data for a model of care for patients with DM and HTN consisting of four main components: case management, patient support and education counseling, integrated mental health, and health promotion. RESULTS: Of 2644 Syrian patients with DM and/or HTN, 8% had Type-1 DM, 30% had Type-2 DM, 30% had HTN and 33% had DM + HTN. At intake, patients had a median age of 53, were predominantly females (63%), mostly from outside the catchment area (70%) and diagnosed (97%) prior to enrollment. After 6 months of care compared to intake: 61% of all patients had controlled DM (HbA1C < 8%) and 50% had controlled blood pressure (BP: < 140/90 mmHg) compared to 29 and 32%, respectively (p < 0.001). Compared to intake, patients with Type-1 DM reached an HbA1C mean of 8.4% versus 9.3% (p = 0.022); Type-2 DM patients had an HbA1C mean of 8.1% versus 9.4% (p = 0.001); and those with DM + HTN reached a mean HbA1C of 7.7% versus 9.0%, (p = 0.003). Reflecting improved control, HTN patients requiring ≥3 medications increased from 23 to 38% (p < 0.001), while DM patients requiring insulin increased from 21 to 29% (p < 0.001). Loss-to-follow-up was 16%. CONCLUSIONS: The MSF model of care for DM and HTN operating in the Shatila refugee camp is feasible, and showed promising outcomes among enrolled individuals. It may be replicated in similar contexts to respond to the increasing burden of NCDs among refugees in the Middle-East and elsewhere.

Epigenetic interplay between histone modifications and DNA methylation in gene silencing.

Knowledge on heritable changes in gene expression that result from epigenetic events is of increasing relevance in the development of strategies for prevention, early diagnosis and treatment of cancer. Histone acetylation and DNA methylation are epigenetic modifications whose patterns can be regarded as heritable marks that ensure accurate transmission of the chromatin states and gene expression profiles over many cell generations. Importantly, patterns and levels of DNA methylation and histone acetylation are profoundly altered in human cancers. Accumulating evidence suggests that an epigenetic cross-talk, i.e. interplay between DNA methylation and histone acetylation, may be involved in the process of gene transcription and aberrant gene silencing in tumours. Although the molecular mechanism of gene activation is relatively well understood, the hierarchical order of events and dependencies leading to gene silencing in the course of cancer development remain largely unknown. While some studies suggest that DNA methylation patterns guide histone modifications (including histone acetylation and methylation) during gene silencing, other studies argue that DNA methylation takes its cues primarily from histone modification states. In this review, we summarize current knowledge on the interplay between DNA methylation and histone modifications during gene silencing and its importance in the integration of environmental and intrinsic stimuli in the control of gene expression. We also discuss the importance of an epigenetic cross-talk in the protection against genetic changes in response to environmental genotoxins as well as the implication for cancer therapy and prevention.

Epigenetic drivers and genetic passengers on the road to cancer.

Cancer is traditionally viewed as a primarily genetic disorder, however it is now becoming accepted that cancer is also a consequence of abnormal epigenetic events. Genetic changes and aneuploidy are associated with alterations in DNA sequence, and they are a hallmark of the malignant process. Epigenetic alterations are universally present in human cancer and result in heritable changes in gene expression and chromatin structure over many cell generations without changes in DNA sequence, leading to functional consequences equivalent to those induced by genetic alterations. Importantly, intriguing evidence emerged suggesting that epigenetic changes may precede and provoke genetic changes. In this scenario, epigenetic events are primary events while genetic changes (such as mutations) may simply be a consequence of disrupted epigenetic states. This fact may explain why many genetic screens proved to be limited with regard to cancer causality and pathogenesis. Aberrant epigenetic events affect multiple genes and cellular pathways in a non-random fashion and this can predispose to induction and accumulation of genetic changes in the course of tumour initiation and progression. These considerations are critical for a better understanding of tumourigenesis and molecular events underlying the acquisition of drug resistance, as well as development of novel strategies for cancer therapy and prevention.

Tissue-specific inactivation of HAT cofactor TRRAP reveals its essential role in B cells.

The transformation/transcription domain-associated protein (TRRAP) is a common component of many histone acetyltransferase (HAT) complexes. Targeted-deletion of the Trrap gene led to early embryonic lethality and revealed a critical function of TRRAP in cell proliferation. Here, we investigate the function of TRRAP in murine B cells. To this end, we ablated Trrap gene in a B cell-restricted manner and studied its impact on B-cell development and proliferation, a pre-requisite for class switch recombination (CSR), the process that allows IgM-expressing B lymphocytes to switch to the expression of IgG, IgE, or IgA isotypes. We show that TRRAP deficiency impairs B-cell development but does not directly affect CSR. Instead, cells induced to proliferate undergo apoptosis. Our findings demonstrate a central and general role of TRRAP in cell proliferation.

Histone modifications and cancer.

It is now widely recognized that epigenetic events are important mechanisms underlying cancer development and progression. Epigenetic information in chromatin includes covalent modifications (such as acetylation, methylation, phosphorylation, and ubiquitination) of core nucleosomal proteins (histones). A recent progress in the field of histone modifications and chromatin research has tremendously enhanced our understanding of the mechanisms underlying the control of key physiological and pathological processes. Histone modifications and other epigenetic mechanisms appear to work together in establishing and maintaining gene activity states, thus regulating a wide range of cellular processes. Different histone modifications themselves act in a coordinated and orderly fashion to regulate cellular processes such as gene transcription, DNA replication, and DNA repair. Interest in histone modifications has further grown over the last decade with the discovery and characterization of a large number of histone-modifying molecules and protein complexes. Alterations in the function of histone-modifying complexes are believed to disrupt the pattern and levels of histone marks and consequently deregulate the control of chromatin-based processes, ultimately leading to oncogenic transformation and the development of cancer. Consistent with this notion, aberrant patterns of histone modifications have been associated with a large number of human malignancies. In this chapter, we discuss recent advances in our understanding of the mechanisms controlling the establishment and maintenance of histone marks and how disruptions of these chromatin-based mechanisms contribute to tumorigenesis. We also suggest how these advances may facilitate the development of novel strategies to prevent, diagnose, and treat human malignancies.

HAT cofactor TRRAP mediates beta-catenin ubiquitination on the chromatin and the regulation of the canonical Wnt pathway.

The Wnt pathway is a key regulator of embryonic development and stem cell self-renewal, and hyperactivation of the Wnt signalling is associated with many human cancers. The central player in the Wnt pathway is beta-catenin, a cytoplasmic protein whose function is tightly controlled by ubiquitination and degradation, however the precise regulation of beta-catenin stability/degradation remains elusive. Here, we report a new mechanism of beta-catenin ubiquitination acting in the context of chromatin. This mechanism is mediated by the histone acetyltransferase (HAT) complex component TRRAP and Skp1, an invariable component of the Skp-Cullin-F-box (SCF) ubiquitin ligase complex. TRRAP interacts with Skp1/SCF and mediates its recruitment to beta-catenin target promoter in chromatin. TRRAP deletion leads to a reduced level of beta-catenin ubiquitination, lower degradation rate and accumulation of beta-catenin protein. Furthermore, recruitment of Skp1 to chromatin and ubiquitination of chromatin-bound beta-catenin are abolished upon TRRAP knock-down, leading to an abnormal retention of beta-catenin at the chromatin and concomitant hyperactivation of the canonical Wnt pathway. These results demonstrate that there is a distinct regulatory mechanism for beta-catenin ubiquitination/ destruction acting in the nucleus which functionally complements cytoplasmic destruction of beta-catenin and prevents its oncogenic stabilization and chronic activation of the canonical Wnt pathway.

Epigenetic information in chromatin: the code of entry for DNA repair.

Epigenetic changes are important etiological factors of human cancer. Epigenetic information in chromatin (known as 'histone code') is a fascinating feature used by cells to extend and modulate the genetic (DNA) code. The histone code is thus proposed to be 'read' by cells to regulate accessibility to, and functions of, chromatin DNA. While the role of the epigenetic code involving chromatin modifying/remodeling complexes in transcriptional regulation is well established, it is only recently that these mechanisms have been implicated in DNA damage detection and DNA repair. However, how the components of the DNA damage sensing and repair machinery gain access to broken DNA in compacted chromatin remains a mystery. Recent studies provide important insights into DNA damage- and repair-specific modifications to histones and shed light on how the epigenetic code controls DNA repair.