Histone deacetylase controls adult stem cell aging by balancing the expression of polycomb genes and jumonji domain containing 3

Aging is linked to loss of the self-renewal capacity of adult stem cells. Here, we observed that human multipotent stem cells (MSCs) underwent cellular senescence in vitro. Decreased expression of histone deacetylases (HDACs), followed by downregulation of polycomb group genes (PcGs), such as BMI1, EZH2 and SUZ12, and by upregulation of jumonji domain containing 3 (JMJD3), was observed in senescent MSCs. Similarly, HDAC inhibitors induced cellular senescence through downregulation of PcGs and upregulation of JMJD3. Regulation of PcGs was associated with HDAC inhibitor-induced hypophosphorylation of RB, which causes RB to bind to and decrease the transcriptional activity of E2F. JMJD3 expression regulation was dependant on histone acetylation status at its promoter regions. A histone acetyltransferase (HAT) inhibitor prevented replicative senescence of MSCs. These results suggest that HDAC activity might be important for MSC self-renewal by balancing PcGs and JMJD3 expression, which govern cellular senescence by p16INK4A regulation

Viral Mediated Redirection of NEMO/IKKγ to Autophagosomes Curtails the Inflammatory Cascade

The early host response to viral infections involves transient activation of pattern recognition receptors leading to an induction of inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα). Subsequent activation of cytokine receptors in an autocrine and paracrine manner results in an inflammatory cascade. The precise mechanisms by which viruses avert an inflammatory cascade are incompletely understood. Nuclear factor (NF)-κB is a central regulator of the inflammatory signaling cascade that is controlled by inhibitor of NF-κB (IκB) proteins and the IκB kinase (IKK) complex. In this study we show that murine cytomegalovirus inhibits the inflammatory cascade by blocking Toll-like receptor (TLR) and IL-1 receptor-dependent NF-κB activation. Inhibition occurs through an interaction of the viral M45 protein with the NF-κB essential modulator (NEMO), the regulatory subunit of the IKK complex. M45 induces proteasome-independent degradation of NEMO by targeting NEMO to autophagosomes for subsequent degradation in lysosomes. We propose that the selective and irreversible degradation of a central regulatory protein by autophagy represents a new viral strategy to dampen the inflammatory response

Histone Deacetylase 3 Depletion in Osteo/Chondroprogenitor Cells Decreases Bone Density and Increases Marrow Fat

Histone deacetylase (Hdac)3 is a nuclear enzyme that contributes to epigenetic programming and is required for embryonic development. To determine the role of Hdac3 in bone formation, we crossed mice harboring loxP sites around exon 7 of Hdac3 with mice expressing Cre recombinase under the control of the osterix promoter. The resulting Hdac3 conditional knockout (CKO) mice were runted and had severe deficits in intramembranous and endochondral bone formation. Calvarial bones were significantly thinner and trabecular bone volume in the distal femur was decreased 75% in the Hdac3 CKO mice due to a substantial reduction in trabecular number. Hdac3-CKO mice had fewer osteoblasts and more bone marrow adipocytes as a proportion of tissue area than their wildtype or heterozygous littermates. Bone formation rates were depressed in both the cortical and trabecular regions of Hdac3 CKO femurs. Microarray analyses revealed that numerous developmental signaling pathways were affected by Hdac3-deficiency. Thus, Hdac3 depletion in osterix-expressing progenitor cells interferes with bone formation and promotes bone marrow adipocyte differentiation. These results demonstrate that Hdac3 inhibition is detrimental to skeletal health

Histone deacetylases in viral infections

Chromatin remodeling and gene expression are regulated by histone deacetylases (HDACs) that condense the chromatin structure by deacetylating histones. HDACs comprise a group of enzymes that are responsible for the regulation of both cellular and viral genes at the transcriptional level. In mammals, a total of 18 HDACs have been identified and grouped into four classes, i.e., class I (HDACs 1, 2, 3, 8), class II (HDACs 4, 5, 6, 7, 9, 10), class III (Sirt1–Sirt7), and class IV (HDAC11). We review here the role of HDACs on viral replication and how HDAC inhibitors could potentially be used as new therapeutic tools in several viral infections

Targeting histone deacetyalses in the treatment of B- and T-cell malignancies

HDAC inhibitors (HDACI) are now emerging as one of the most promising new classes of drugs for the treatment of select forms of non-Hodgkin’s lymphoma (NHL). They are particularly active in T-cell lymphomas, possibly hodgkin’s lymphoma and indolent B cell lymphomas. Presently, two of these agents, vorinostat and romidepsin, have been approved in the US for the treatment of relapsed and refractory cutaneous T cell lymphomas (CTCL). Initially, these agents were developed with the idea that they affected transcriptional activation and thus gene expression, by modulating chromatin condensation and decondensation. It is now clear that their effects go beyond chromatin and by affecting the acetylation status of histones and other intra-cellular proteins, they modify gene expression and cellular function via multiple pathways. Gene expression profiles and functional genetic analysis has led to further understanding of the various molecular pathways that are affected by these agents including cell cycle regulation, pathways of cellular proliferation, apoptosis and angiogenesis all important in lymphomagenesis. There is also increasing data to support the effects of these agents on T cell receptor and immune function which may explain the high level of activity of these agents in T cell lymphomas and hodgkin’s lymphoma. There is ample evidence of epigenetic dysregulation in lymphomas which may underlie the mechanisms of action of these agents but how these agents work is still not clear. Current HDAC inhibitors can be divided into at least four classes based on their chemical structure. At present several of these HDAC inhibitors are in clinical trials both as single agents and in combination with chemotherapy or other biological agents. They are easy to administer and are generally well tolerated with minimal side effects. Different dosing levels and schedules and the use of isospecific HDAC inhibitors are some of the strategies that are being employed to increase the therapeutic effect of these agents in the treatment of lymphomas. There may also be class differences that translate into specific activity against different lymphoma. HDAC inhibitors will likely be incorporated into combinations of targeted therapies both in the upfront and relapsed setting for lymphomas

Epigenetic regulation of caloric restriction in aging

The molecular mechanisms of aging are the subject of much research and have facilitated potential interventions to delay aging and aging-related degenerative diseases in humans. The aging process is frequently affected by environmental factors, and caloric restriction is by far the most effective and established environmental manipulation for extending lifespan in various animal models. However, the precise mechanisms by which caloric restriction affects lifespan are still not clear. Epigenetic mechanisms have recently been recognized as major contributors to nutrition-related longevity and aging control. Two primary epigenetic codes, DNA methylation and histone modification, are believed to dynamically influence chromatin structure, resulting in expression changes of relevant genes. In this review, we assess the current advances in epigenetic regulation in response to caloric restriction and how this affects cellular senescence, aging and potential extension of a healthy lifespan in humans. Enhanced understanding of the important role of epigenetics in the control of the aging process through caloric restriction may lead to clinical advances in the prevention and therapy of human aging-associated diseases

Human Cytomegalovirus IE1 Protein Elicits a Type II Interferon-Like Host Cell Response That Depends on Activated STAT1 but Not Interferon-γ

Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary infection, establishes life-long persistence in all infected individuals. Acute hCMV infections cause a variety of diseases in humans with developmental or acquired immune deficits. In addition, persistent hCMV infection may contribute to various chronic disease conditions even in immunologically normal people. The pathogenesis of hCMV disease has been frequently linked to inflammatory host immune responses triggered by virus-infected cells. Moreover, hCMV infection activates numerous host genes many of which encode pro-inflammatory proteins. However, little is known about the relative contributions of individual viral gene products to these changes in cellular transcription. We systematically analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major transcriptional activator and antagonist of type I interferon (IFN) signaling, on the human transcriptome. Following expression under conditions closely mimicking the situation during productive infection, IE1 elicits a global type II IFN-like host cell response. This response is dominated by the selective up-regulation of immune stimulatory genes normally controlled by IFN-γ and includes the synthesis and secretion of pro-inflammatory chemokines. IE1-mediated induction of IFN-stimulated genes strictly depends on tyrosine-phosphorylated signal transducer and activator of transcription 1 (STAT1) and correlates with the nuclear accumulation and sequence-specific binding of STAT1 to IFN-γ-responsive promoters. However, neither synthesis nor secretion of IFN-γ or other IFNs seems to be required for the IE1-dependent effects on cellular gene expression. Our results demonstrate that a single hCMV protein can trigger a pro-inflammatory host transcriptional response via an unexpected STAT1-dependent but IFN-independent mechanism and identify IE1 as a candidate determinant of hCMV pathogenicity

HCMV IL-10 Suppresses Cytokine Expression in Monocytes Through Inhibition of Nuclear Factor-κB

Modulation of host immune responses is a common strategy for promoting virus persistence and avoiding clearance. Human cytomegalovirus (HCMV) is known to encode numerous immunomodulatory genes, including a homolog of the cytokine human interleukin-10 (hIL-10). While having limited sequence homology to hIL-10, cytomegalovirus IL-10 (cmvIL-10) shares many functional characteristics with the human cytokine and acts as a potent suppressor of the inflammatory immune response. The mechanism by which hIL-10 inhibits inflammatory cytokines involves a transcriptional block via inhibition of nuclear factor-κB (NF-κB) activity. To determine whether cmvIL-10 employs the same mechanism to inhibit cytokine production, the effect of cmvIL-10 on NF-κB signaling in monocytes was investigated. The results demonstrate that cmvIL-10 does inhibit NF-κB activation, as evidenced by reduced degradation of the NF-κB inhibitor IκB-α, and decreased transcription of the NF-κB–responsive genes tumor necrosis factor-α (TNF-α) and IL-1β. These studies confirm that cmvIL-10 mediates cytokine suppression by blocking NF-κB transcriptional activity in human monocytes