Inhibition of Mono-ADP-Ribosyltransferase Activity during the Execution Phase of Apoptosis Prevents Apoptotic Body Formation

Advances in biological functions and applications of apoptotic vesicles

BACKGROUND

Apoptotic vesicles are extracellular vesicles generated by apoptotic cells that were previously regarded as containing waste or harmful substances but are now thought to play an important role in signal transduction and homeostasis regulation.

METHODS

In the present review, we reviewed many articles published over the past decades on the subtypes and formation of apoptotic vesicles and the existing applications of these vesicles.

RESULTS

Apoptotic bodies were once regarded as vesicles released by apoptotic cells, however, apoptotic vesicles are now regarded to include apoptotic bodies, apoptotic microvesicles and apoptotic exosomes, which exhibit variation in terms of biogenesis, sizes and properties. Applications of apoptotic vesicles were first reported long ago, but such reports have been rarer than those of other extracellular vesicles. At present, apoptotic vesicles have been utilized mainly in four aspects, including in direct therapeutic applications, in their engineering as carriers, in their construction as vaccines and in their utilization in diagnosis.

CONCLUSION

Building on a deeper understanding of their composition and characteristics, some studies have utilized apoptotic vesicles to treat diseases in more novel ways. However, their limitations for clinical translation, such as heterogeneity, have also emerged. In general, apoptotic vesicles have great application potential, but there are still many barriers to overcome in their investigation. Video Abstract.

ART3 regulates triple-negative breast cancer cell function via activation of Akt and ERK pathways

Triple-negative breast cancers (TNBCs) are defined by lack of expressions of estrogen, progesterone, and ERBB2 receptors. Because biology of TNBC is poorly understood, no targeted therapy has been developed for this breast cancer subtype and chemotherapy is its only systemic treatment modality. In this study, we firstly determined that the expression of human ecto-ADP-ribosyltransferase 3 (ART3) is significantly associated with the basal-like breast cancer subgroup, which is largely overlapped with TNBC, through analyzing published data sets. We also found that ART3 protein is significantly overexpressed in human TNBC tumors tissue and cell lines through using immunohistochemistry and immunoblotting. Overexpression of ART3 in MDA-MB-231 breast cancer cells increased cell proliferation, invasion, and survival in vitro and growth of xenograft tumors. Conversely, knockdown of ART3 in breast cancer cells inhibited cell proliferation and invasion. In addition, we showed that ART 3 overexpression activated AKT and ERK in vitro and in xenograft tumors. Together, our findings demonstrate that ART3 is a critical TNBC marker with functional significance.

The expression pattern of ADP-ribosyltransferase 3 in rat traumatic brain injury

Mammalian ecto ADP-ribosyltransferases (ARTs) can regulate the biological functions of various types of cells by catalyzing the transfer of single ADP-ribose moiety from NAD+ to a specific amino acid in a target protein. ART3 is a member of the known ART family which is involved in cell division, DNA-repair and the regulation of the inflammatory response. To elucidate the expression, cellular localization and possible functions of ART3 in central nervous system (CNS) lesion and repair, we performed an acute traumatic brain injury model in adult rats. Western blot analysis showed that the expression of ART3 in ipsilateral brain cortex increased, then reached a peak at day 3 after traumatic brain injury (TBI), and gradually declined during the following days. But in the contralateral brain cortex, no obvious alterations were observed. Immunohistochemistry revealed the highly significant accumulation of ART3 at the ipsilateral brain in comparison to contralateral cerebral cortex. Double immunofluorescence labeling suggested that ART3 was localized mainly in the plasmalemma of neurons, but not in astrocytes or microglias within 3 mm from the lesion site at day 3 post-injury. In addition, we detected the expression profiles of caspase-3 and growth associated protein 43 (GAP-43) whose changes were correlated with the expression profiles of ART3 in this TBI model. Besides, co-localization of ART3/active caspase-3 and ART3/GAP43 were detected in NeuN-positive cells, respectively. Moreover, Pheochromocytoma (PC12) cells were treated with H₂O₂ to establish an apoptosis model. The results showed that the expression of ART3 was increased in the concentration and time dependence way. To further examine the involvement of ART3 in apoptosis of PC12, 3-Methoxybenzamide was used in flow cytometry analysis of apoptotic cells stained with Annexin V and PI. The experimental group in which 3-Methoxybenzamide used had a relative low level of apoptotic index compared with the untreated group. Together with previous reports, we hypothesize that ART3 may play important roles in CNS pathophysiology after TBI and further research is needed to have a good understanding of its function and mechanism.

Nuclear ADP-ribosylation reactions in mammalian cells: where are we today and where are we going?

Since poly-ADP ribose was discovered over 40 years ago, there has been significant progress in research into the biology of mono- and poly-ADP-ribosylation reactions. During the last decade, it became clear that ADP-ribosylation reactions play important roles in a wide range of physiological and pathophysiological processes, including inter- and intracellular signaling, transcriptional regulation, DNA repair pathways and maintenance of genomic stability, telomere dynamics, cell differentiation and proliferation, and necrosis and apoptosis. ADP-ribosylation reactions are phylogenetically ancient and can be classified into four major groups: mono-ADP-ribosylation, poly-ADP-ribosylation, ADP-ribose cyclization, and formation of O-acetyl-ADP-ribose. In the human genome, more than 30 different genes coding for enzymes associated with distinct ADP-ribosylation activities have been identified. This review highlights the recent advances in the rapidly growing field of nuclear mono-ADP-ribosylation and poly-ADP-ribosylation reactions and the distinct ADP-ribosylating enzyme families involved in these processes, including the proposed family of novel poly-ADP-ribose polymerase-like mono-ADP-ribose transferases and the potential mono-ADP-ribosylation activities of the sirtuin family of NAD(+)-dependent histone deacetylases. A special focus is placed on the known roles of distinct mono- and poly-ADP-ribosylation reactions in physiological processes, such as mitosis, cellular differentiation and proliferation, telomere dynamics, and aging, as well as "programmed necrosis" (i.e., high-mobility-group protein B1 release) and apoptosis (i.e., apoptosis-inducing factor shuttling). The proposed molecular mechanisms involved in these processes, such as signaling, chromatin modification (i.e., "histone code"), and remodeling of chromatin structure (i.e., DNA damage response, transcriptional regulation, and insulator function), are described. A potential cross talk between nuclear ADP-ribosylation processes and other NAD(+)-dependent pathways is discussed.

Oxidative stress is not required for the induction of apoptosis upon glutamine starvation of Sp2/0-Ag14 hybridoma cells

L-glutamine (Gln) withdrawal rapidly triggers apoptosis in the murine hybridoma cell line Sp2/0-Ag14 (Sp2/0). In this report, we examined the possibility that Gln deprivation of Sp2/0 cells triggers an oxidative stress which would contribute to the activation of apoptotic pathways. Gln withdrawal triggered an oxidative stress in Sp2/0 cells, as indicated by an increased accumulation of reactive oxygen species (ROS) and an increase in the intracellular content in protein carbonyl groups. Gln starvation also caused a decrease in the intracellular levels of glutathione (GSH). However, a decrease in GSH was not sufficient to induce Sp2/0 cell death since reducing GSH levels with DL-buthionine-[S,R]-sulfoximine did not affect cell viability. The antioxidant N-acetyl-L-cysteine (NAC), while effective in inhibiting ROS accumulation and oxidative stress, did not prevent the loss in cell viability or the processing and activation of caspase-3 triggered by Gln starvation. On the other hand, NAC did reduce the formation of apoptotic bodies in dying cells. Altogether these results indicate that in Sp2/0 cells, Gln deprivation leads to the induction of an oxidative stress which, while involved in the formation of apoptotic bodies, is not essential to the activation of the cell death program.

Cloning and characterization of an Arabidopsis thaliana Nudix hydrolase homologous to the mammalian GFG protein

In a search for a plant antimutator MutT protein, an Arabidopsis thaliana Nudix hydrolase with homology to the mammalian GFG protein was expressed as a hexahistidine fusion polypeptide in Escherichia coli and purified to homogeneity. Unlike the GFG protein, the A. thaliana homolog could not complement the mutT mutation in a MutT-deficient E. coli strain nor was it able to hydrolyze 8-oxo-dGTP, the main substrate of the MutT protein. Instead the recombinant protein hydrolyzed a variety of nucleoside diphosphate derivatives showing a preference for ADP-ribose, with Km and k(cat) values of 1.2 mM and 2.7 s(-1) respectively. The products of ADP-ribose hydrolysis were AMP and ribose-5-phosphate. The optimal activity was at alkaline pH (8.5) with Mg2+ (5 mM) ions as the cofactor. The protein exists as a dimmer in solution.

Gene expression profiles of apoptotic neurons

The multigenic program underlying neuronal apoptosis is mostly unknown. To study the program, we used genome-scale screening by oligonucleotide microarrays during serum and potassium deprivation-induced apoptosis of cerebellar granule neurons. From the 8740 genes interrogated by the arrays, 423 genes were found to be regulated at both the transcriptional and the posttranscriptional level and segregated into distinct clusters. Semantic clustering based on gene ontologies showed coordinated expression of genes with common biological functions and metabolic pathways. Among the genes implicated in apoptotic cerebellar granule neurons, 70 were in common with those differentially expressed in cortical neurons exposed to amyloid beta-protein, indicating the existence of common mechanisms responsible for neuronal cell death. Our results offer a genomic view of the changes that accompany neuronal apoptosis and yield new insights into the underlying molecular basis.

Catalytic topoisomerase II inhibitors in cancer therapy

The nuclear enzyme DNA topoisomerase II is a major target for antineoplastic agents. All topoisomerase II-directed agents are able to interfere with at least one step of the catalytic cycle. Agents able to stabilize the covalent DNA topoisomerase II complex (also known as the cleavable complex) are traditionally called topoisomerase II poisons, while agents acting on any of the other steps in the catalytic cycle are called catalytic inhibitors. Thus, catalytic topoisomerase II inhibitors are a heterogeneous group of compounds that might interfere with the binding between DNA and topoisomerase II (aclarubicin and suramin), stabilize noncovalent DNA topoisomerase II complexes (merbarone, ICRF-187, and structurally related bisdioxopiperazine derivatives), or inhibit ATP binding (novobiocin). Some, such as fostriecin, may also have alternative biological targets. Whereas topoisomerase II poisons are used solely for their antitumor activities, catalytic inhibitors are utilized for a variety of reasons, including their activity as antineoplastic agents (aclarubicin and MST-16), cardioprotectors (ICRF-187), or modulators in order to increase the efficacy of other agents (suramin and novobiocin). In this review, the mechanism and biological activity of different catalytic inhibitors is described, with emphasis on therapeutically used compounds. We will then discuss future development and applications of this interesting class of compounds.

Functional aspects of protein mono-ADP-ribosylation

Mono-ADP-ribosylation is the enzymatic transfer of ADP-ribose from NAD(+) to acceptor proteins. It is catalysed by cellular ADP-ribosyltransferases and certain bacterial toxins. There are two subclasses of cellular enzymes: the ectoenzymes that modify targets such as integrins, defensin and other cell surface molecules; and the intracellular enzymes that act on proteins involved in cell signalling and metabolism, such as the beta-subunit of heterotrimeric G proteins, GRP78/BiP and elongation factor 2. The genes that encode the ectoenzymes have been cloned and their protein products are well characterized, yet little is known about the intracellular ADP-ribosyltransferases, which may be part of a novel protein family with an important role in regulating cell function. ADP-ribosylation usually leads to protein inactivation, providing a mechanism to inhibit protein functions in both physiological and pathological conditions.