Apoptosis is a fundamental process for metazoan development. It is also relevant to the pathophysiology of immune diseases and cancers and to the outcome of cancer chemotherapies, as well as being a ...target for cancer therapies. Apoptosis involves intrinsic pathways typically initiated by DNA damaging agents and engaging mitochondria, and extrinsic pathways typically initiated by “death receptors” and their ligands TRAIL and TNF at the cell surface. Recently, we discovered the apoptotic ring, which microscopically looks like a nuclear annular staining early in apoptosis. This ring is, in three-dimensional space, a thick intranuclear shell consisting of epigenetic modifications including histone H2AX and DNA damage response (DDR) proteins. It excludes the DNA repair factors usually associated with γ-H2AX in the DDR nuclear foci. Here, we summarize our knowledge of the apoptotic ring, and discuss its biological and pathophysiological relevance, as well as its value as a potential pharmacodynamic biomarker for anticancer therapies.
We recently showed that histone H2AX phosphorylated on serine 139 (γ-H2AX), a hallmark of DNA damage response (DDR), also forms early during apoptosis induced by death receptor activation. Here, we ...extend and discuss our findings on apoptotic γ-H2AX, which differs from the well-established DDR with nuclear foci. During apoptosis induced by death receptors agonists (TRAIL and FasL) and staurosporine, γ-H2AX is initiated in the nuclear periphery immediately inside the nuclear envelope while total H2AX remains distributed throughout the nucleus. This process is readily detectable by immunofluorescence microscopy and we refer to it as the "γ-H2AX ring". It is conserved both in cancer and normal cells. The γ-H2AX ring contains the activated checkpoints kinases, ATM, Chk2 and DNA-PK; the latter being the main effector for the apoptotic γ-H2AX phosphorylation. Notably, we show here that the γ-H2AX ring coincides with phosphorylated H2B on serine 14 (PS14-H2B), another histone modification associated with apoptosis. The coordinated phosphorylations of H2AX and H2B suggest a previously unrecognized histone phosphorylation signature for apoptosis consisting of γ-H2AX together with PS14-H2B and possibly PY142-H2AX. This signature ("phospho-histone 2 code") together with the γ-H2AX ring provides a new feature to monitor and study apoptosis.
Subtle caspase activation is associated with the differentiation of several myeloid lineages. A tightly orchestrated dance between caspase-3 activation and the chaperone HSP70 that migrates to the ...nucleus to protect the master regulator GATA-1 from cleavage transiently occurs in basophilic erythroblasts and may prepare nucleus and organelle expel that occurs at the terminal phase of erythroid differentiation. A spatially restricted activation of caspase-3 occurs in maturing megakaryocytes to promote proplatelet maturation and platelet shedding in the bloodstream. In a situation of acute platelet need, caspase-3 could be activated in response to IL-1α and promote megakaryocyte rupture. In peripheral blood monocytes, colony-stimulating factor-1 provokes the formation of a molecular platform in which caspase-8 is activated, which downregulates nuclear factor-kappa B (NF-κB) activity and activates downstream caspases whose target fragments such as those generated by nucleophosmin (NPM1) cleavage contribute to the generation of resting macrophages. Human monocytes secrete mature IL-1β in response to lipopolysaccharide through an alternative inflammasome activation that involves caspase-8, a pathway that does not lead to cell death. Finally, active caspase-3 is part of the proteases contained in secretory granules of mast cells. Many questions remain on how these proteases are activated in myeloid cell lineages, which target proteins are cleaved, whereas other are protected from proteolysis, the precise role of cleaved proteins in cell differentiation and functions, and the link between these non-apoptotic functions of caspases and the death of these diverse cell types. Better understanding of these functions may generate therapeutic strategies to control cytopenias or modulate myeloid cell functions in various pathological situations.
The cytidine analogues azacytidine and 5-aza-2'-deoxycytidine (decitabine) are commonly used to treat myelodysplastic syndromes, with or without a myeloproliferative component. It remains unclear ...whether the response to these hypomethylating agents results from a cytotoxic or an epigenetic effect. In this study, we address this question in chronic myelomonocytic leukaemia. We describe a comprehensive analysis of the mutational landscape of these tumours, combining whole-exome and whole-genome sequencing. We identify an average of 14±5 somatic mutations in coding sequences of sorted monocyte DNA and the signatures of three mutational processes. Serial sequencing demonstrates that the response to hypomethylating agents is associated with changes in DNA methylation and gene expression, without any decrease in the mutation allele burden, nor prevention of new genetic alteration occurence. Our findings indicate that cytosine analogues restore a balanced haematopoiesis without decreasing the size of the mutated clone, arguing for a predominantly epigenetic effect.
γH2AX and cancer Bonner, William M; Redon, Christophe E; Dickey, Jennifer S ...
Nature reviews. Cancer,
12/2008, Letnik:
8, Številka:
12
Journal Article
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Odprti dostop
Histone H2AX phosphorylation on a serine four residues from the carboxyl terminus (producing γH2AX) is a sensitive marker for DNA double-strand breaks (DSBs). DSBs may lead to cancer but, ...paradoxically, are also used to kill cancer cells. Using γH2AX detection to determine the extent of DSB induction may help to detect precancerous cells, to stage cancers, to monitor the effectiveness of cancer therapies and to develop novel anticancer drugs.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Cancers display intratumoral and intertumoral heterogeneity, which poses challenges to small-molecule intervention. Studying drug responses on a whole-genome and transcriptome level using ...next-generation sequencing has revolutionized our understanding of how small molecules intervene in cells, which helps us to study and potentially predict treatment outcomes. Some small molecules act directly at the genomic level by targeting DNA or chromatin proteins. Here, we review recent advances in establishing whole-genome and transcriptome maps of small-molecule targets, comprising chromatin components or downstream events. We also describe recent advances in studying drug responses using single-cell RNA and DNA sequencing. Furthermore, we discuss how this fundamental research can be taken forward to devise innovative personalized treatment modalities.
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Recently, we identified the "apoptotic ring," containing phosphorylated histone H2AX (γ-H2AX), as an early chromatin modification during apoptosis. Because γ-H2AX initiates the DNA damage response ...(DDR), we tested whether the apoptotic H2AX response leads to the full recruitment of the DDR factors that normally coordinate DNA repair and cell-cycle checkpoints. We show that the apoptotic H2AX response does not recruit the DDR factors because MDC1 (mediator of DNA damage checkpoint protein 1), which normally binds to γ-H2AX in response to DNA damage and amplifies the DDR, is cleaved by caspase-3. This cleavage separates the BRCT and FHA domains of MDC1 and constitutes a novel mechanism for the inactivation of DNA repair in apoptotic cells. Also, we show that downregulation of MDC1 increases the apoptotic response to TRAIL. Together, these results implicate MDC1 in the cellular apoptotic response.
Inflammation is a complex physiological process triggered in response to harmful stimuli
. It involves cells of the immune system capable of clearing sources of injury and damaged tissues. Excessive ...inflammation can occur as a result of infection and is a hallmark of several diseases
. The molecular bases underlying inflammatory responses are not fully understood. Here we show that the cell surface glycoprotein CD44, which marks the acquisition of distinct cell phenotypes in the context of development, immunity and cancer progression, mediates the uptake of metals including copper. We identify a pool of chemically reactive copper(II) in mitochondria of inflammatory macrophages that catalyses NAD(H) redox cycling by activating hydrogen peroxide. Maintenance of NAD
enables metabolic and epigenetic programming towards the inflammatory state. Targeting mitochondrial copper(II) with supformin (LCC-12), a rationally designed dimer of metformin, induces a reduction of the NAD(H) pool, leading to metabolic and epigenetic states that oppose macrophage activation. LCC-12 interferes with cell plasticity in other settings and reduces inflammation in mouse models of bacterial and viral infections. Our work highlights the central role of copper as a regulator of cell plasticity and unveils a therapeutic strategy based on metabolic reprogramming and the control of epigenetic cell states.
The “apoptotic ring” is characterized by the phosphorylation of histone H2AX at serine 139 (γ-H2AX) by DNA-dependent protein kinase (DNA-PK). The γ-H2AX apoptotic ring differs from the nuclear foci ...patterns observed in response to DNA-damaging agents. It contains phosphorylated DNA damage response proteins including activated Chk2, activated ATM, and activated DNA-PK itself but lacks MDC1 and 53BP1, which are required to initiate DNA repair. Because DNA-PK can phosphorylate heat shock protein 90α (HSP90α) in biochemical assays, we investigated whether HSP90α is involved in the apoptotic ring. Here we show that HSP90α is phosphorylated by DNA-PK on threonines 5 and 7 early during apoptosis and that both phosphorylated HSP90α and DNA-PK colocalize in the apoptotic ring. We also show that DNA-PK is a client of HSP90α and that HSP90α is required for full DNA-PK activation, γ-H2AX formation, DNA fragmentation, and apoptotic body formation. In contrast, HSP90 inhibition by geldanamycin markedly enhances TRAIL-induced DNA-PK and H2AX activation. Together, our results reveal that HSP90α is a substrate and chaperone of DNA-PK in the apoptotic response. The response of phosphorylated HSP90α to TRAIL and its localization to the γ-H2AX ring represent epigenetic features of apoptosis that offer insights for studying and monitoring nuclear apoptosis.
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