Histone deacetylase inhibitors augment doxorubicin-induced DNA damage in cardiomyocytes

Histone deacetylase inhibitors have emerged as a new class of anticancer therapeutics with suberoylanilide hydroxamic acid (Vorinostat) and depsipeptide (Romidepsin) already being approved for clinical use. Numerous studies have identified that histone deacetylase inhibitors will be most effective in the clinic when used in combination with conventional cancer therapies such as ionizing radiation and chemotherapeutic agents. One promising combination, particularly for hematologic malignancies, involves the use of histone deacetylase inhibitors with the anthracycline, doxorubicin. However, we previously identified that trichostatin A can potentiate doxorubicin-induced hypertrophy, the dose-limiting side-effect of the anthracycline, in cardiac myocytes. Here we have the extended the earlier studies and evaluated the effects of combinations of the histone deacetylase inhibitors, trichostatin A, valproic acid and sodium butyrate on doxorubicin-induced DNA double-strand breaks in cardiomyocytes. Using γH2AX as a molecular marker for the DNA lesions, we identified that all of the broad-spectrum histone deacetylase inhibitors tested augment doxorubicin-induced DNA damage. Furthermore, it is evident from the fluorescence photomicrographs of stained nuclei that the histone deacetylase inhibitors also augment doxorubicin-induced hypertrophy. These observations highlight the importance of investigating potential side-effects, in relevant model systems, which may be associated with emerging combination therapies for cancer.     

Histone deacetylase signaling in cardioprotection

Cardiovascular disease (CVD) represents a major challenge for health care systems, both in terms of the high mortality associated with it and the huge economic burden of its treatment. Although CVD represents a diverse range of disorders, they share common compensatory changes in the heart at the structural, cellular, and molecular level that, in the long term, can become maladaptive and lead to heart failure. Treatment of adverse cardiac remodeling is therefore an important step in preventing this fatal progression. Although previous efforts have been primarily focused on inhibition of deleterious signaling cascades, the stimulation of endogenous cardioprotective mechanisms offers a potent therapeutic tool. In this review, we discuss class I and class II histone deacetylases, a subset of chromatin-modifying enzymes known to have critical roles in the regulation of cardiac remodeling. In particular, we discuss their molecular modes of action and go on to consider how their inhibition or the stimulation of their intrinsic cardioprotective properties may provide a potential therapeutic route for the clinical treatment of CVD.     

Programmed cell death

Programmed cell death     

Apoptotic and necrotic cell death induced by death domain receptors

Apoptosis and necrosis are two distinct forms of cell death. Caspases are indispensable as initiators and effectors of apoptotic cell death and are involved in many of the morphological and biochemical features of apoptosis. Major changes in mitochondrial membrane integrity and release of proapoptotic factors, such as cytochrome c from the mitochondrial intermembrane space, play an important sensor and amplifying role during apoptotic cell death. In vitro studies of cell death in cell lines have revealed that inhibition of the classical caspase-dependent apoptotic pathway leads in several cases to necrotic cell death. Thus, the same cell death stimulus can result either in apoptotic or necrotic cell death, depending on the availability of activated caspase. Therefore, death domain receptors may initiate an active caspase-independent necrotic signaling pathway. In this review, we describe what is known about the apoptotic and necrotic cell death pathways. Principal elements of necrosis include mitochondrial oxidative phosphorylation, reactive oxygen production, and non-caspase proteolytic cascades depending on serine proteases, calpains, or cathepsins.     

Mitochondrial dynamics in cell death and neurodegeneration

Mitochondria are highly dynamic organelles that continuously undergo two opposite processes, fission and fusion. Mitochondrial dynamics influence not only mitochondrial morphology, but also mitochondrial biogenesis, mitochondrial distribution within the cell, cell bioenergetics, and cell injury or death. Drp1 mediates mitochondrial fission, whereas Mfn1/2 and Opa1 control mitochondrial fusion. Neurons require large amounts of energy to carry out their highly specialized functions. Thus, mitochondrial dysfunction is a prominent feature in a variety of neurodegenerative diseases. Mutations of Mfn2 and Opa1 lead to neuropathies such as Charcot-Marie-Tooth disease type 2A and autosomal dominant optic atrophy. Moreover, both Aβ peptide and mutant huntingtin protein induce mitochondrial fragmentation and neuronal cell death. In addition, mutants of Parkinson’s disease-related genes also show abnormal mitochondrial morphology. This review highlights our current understanding of abnormal mitochondrial dynamics relevant to neuronal synaptic loss and cell death in neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease and Huntington’s disease.     

Immunogenicity of necrotic cell death

The mode of tumor cell death has significant effects on anti-tumor immunity. Although, previously it was thought that cell death is an inert effect, different investigators have clearly shown that dying tumors can attract, activate and mature professional antigen presenting cells and dendritic cells. In addition, others and we have shown that the type of tumor cell death not only controls the presence or absence of specific tumor antigens, but also can result in immunological responses ranging from immunosuppression to anti-tumor immunity. More importantly, it is possible to enhance anti-tumor immunity both in vitro and in vivo by targeting specific molecular mechanisms such as oligopeptidases and the proteasome. These studies not only extend our knowledge on basic immunological questions and the induction of anti-tumor immunity, but also have implications for all types of cancer treatments, in which rapid tumor cell death is induced. This review is a comprehensive summary of cell death and particularly necrosis and the pivotal role it plays in anti-tumor immunity.     

Mitochondrial control of caspase-dependent and -independent cell death

Mitochondria control whether a cell lives or dies. The role mitochondria play in deciding the fate of a cell was first identified in the mid-1990s, because mitochondria-enriched fractions were found to be necessary for activation of death proteases, the caspases, in a cell-free model of apoptotic cell death. Mitochondrial involvement in apoptosis was subsequently shown to be regulated by Bcl-2, a protein that was known to contribute to cancer in specific circumstances. The important role of mitochondria in promoting caspase activation has therefore been a major focus of apoptosis research; however, it is also clear that mitochondria contribute to cell death by caspase-independent mechanisms. In this review, we will highlight recent findings and discuss the mechanism underlying the mitochondrial control of apoptosis and caspase-independent cell death.     

Pathophysiology of mitochondrial cell death control

Mitochondria have been recently recognized to play a major role in the control of apoptosis or programmed cell death. Permeabilization of mitochondrial membranes, a decisive feature of early cell death, is regulated by members of the Bcl-2 family which interact with the permeability transition pore complex (PTPC). Thus, the cytoprotective oncoprotein Bcl-2 stabilizes the mitochondrial membrane barrier function, whereas the tumor suppressor protein Bax permeabilizes mitochondrial membranes. The regulation of membrane permeabilization is intertwined with that of the bioenergetic and redox functions of mitochondria. The implications of alterations in the composition of the PTPC and in mitochondrial function for the pathophysiology of cancer (reduced apoptosis) and neurodegeneration (enhanced apoptosis) are discussed.     

Polyamines in cell growth and cell death: molecular mechanisms and therapeutic applications

Polyamines are aliphatic cations with multiple functions and are essential for life. Cellular polyamine levels are regulated by multiple pathways such as synthesis from amino acid precursors, cellular uptake mechanisms that salvage polyamines from diet and intestinal microorganisms, as well as stepwise degradation and efflux. Investigations using polyamine biosynthetic inhibitors indicate that alterations in cellular polyamine levels modulate normal and cancer cell growth. Studies using transgenic mice overexpressing polyamine biosynthetic enzymes support a role of polyamines in carcinogenesis. Many, if not all, signal transduction pathways intersect with polyamine biosynthetic pathways and the regulation of intracellular polyamine levels. Direct binding of polyamines to DNA and their ability to modulate DNA-protein interactions appear to be important in the molecular mechanisms of polyamine action in cell proliferation. Consistent with the role of polyamines as facilitators of cell growth, several studies have shown their ability to protect cells from apoptosis. However, polyamines also have a role in facilitating cell death. The basis of these diverse cellular responses is currently not known. Cell death response might be partly mediated by the production of hydrogen peroxide during polyamine catabolism. In addition, the ability of polyamines to alter DNA-protein and protein-protein interactions might be disruptive to cellular functions, when abnormally high levels are accumulated due to defects in polyamine catabolic or efflux pathways. A large body of data indicates that polyamine pathway can be a molecular target for therapeutic intervention in several types cancers. Inhibitors of biosynthesis, polyamine analogues as well as oligonucleotide/polyamine analogue combinations are promising drug candidates for chemoprevention and/or treatment of cancer.     

Transglutaminase induction by various cell death and apoptosis pathways

Clarification of the molecular details of forms of natural cell death, including apoptosis, has become one of the most challenging issues of contemporary biomedical sciences. One of the effector elements of various cell death pathways is the covalent cross-linking of cellular proteins by transglutaminases. This review will discuss the accumulating data related to the induction and regulation of these enzymes, particularly of tissue type transglutaminase, in the molecular program of cell death. A wide range of signalling pathways can lead to the parallel induction of apoptosis and transglutaminase, providing a handle for better understanding the exact molecular interactions responsible for the mechanism of regulated cell death.