Staurosporine induces necroptotic cell death under caspase-compromised conditions in U937 cells.

For a long time necrosis was thought to be an uncontrolled process but evidences recently have revealed that necrosis can also occur in a regulated manner. Necroptosis, a type of programmed necrosis is defined as a death receptor-initiated process under caspase-compromised conditions. The process requires the kinase activity of receptor-interacting protein kinase 1 and 3 (RIPK1 and RIPK3) and mixed lineage kinase domain-like protein (MLKL), as a substrate of RIPK3. The further downstream events remain elusive. We applied known inhibitors to characterize the contributing enzymes in necroptosis and their effect on cell viability and different cellular functions were detected mainly by flow cytometry. Here we report that staurosporine, the classical inducer of intrinsic apoptotic pathway can induce necroptosis under caspase-compromised conditions in U937 cell line. This process could be hampered at least partially by the RIPK1 inhibitor necrotstin-1 and by the heat shock protein 90 kDa inhibitor geldanamycin. Moreover both the staurosporine-triggered and the classical death ligand-induced necroptotic pathway can be effectively arrested by a lysosomal enzyme inhibitor CA-074-OMe and the recently discovered MLKL inhibitor necrosulfonamide. We also confirmed that the enzymatic role of poly(ADP-ribose)polymerase (PARP) is dispensable in necroptosis but it contributes to membrane disruption in secondary necrosis. In conclusion, we identified a novel way of necroptosis induction that can facilitate our understanding of the molecular mechanisms of necroptosis. Our results shed light on alternative application of staurosporine, as a possible anticancer therapeutic agent. Furthermore, we showed that the CA-074-OMe has a target in the signaling pathway leading to necroptosis. Finally, we could differentiate necroptotic and secondary necrotic processes based on participation of PARP enzyme.

The guanine-quadruplex structure in the human c-myc gene's promoter is converted into B-DNA form by the human poly(ADP-ribose)polymerase-1.

The important regulatory role of the guanine-quadruplex (GQ) structure, present in the nuclease hypersensitive element (NHE) III(1) region of the human c-myc (h c-myc) gene's promoter, in the regulation of the transcription of that gene has been documented. Here we present evidences, that the human nuclear poly(ADP-ribose)polymerase-1 (h PARP-1) protein participates in the regulation of the h c-myc gene expression through its interaction with this GQ structure, characterized by binding assays, fluorescence energy transfer (FRET) experiments and by affinity pull-down experiments in vitro, and by chromatin immunoprecipitation (ChIP)-qPCR analysis and h c-myc-promoter-luciferase reporter determinations in vivo. We surmise that h PARP-1 binds to the GQ structure and participates in the conversion of that structure into the transcriptionally more active B-DNA form. The first Zn-finger structure present in h PARP-1 participates in this interaction. PARP-1 might be a new member of the group of proteins participating in the regulation of transcription through their interactions with GQ structures present in the promoters of different genes.

Necroptosis: biochemical, physiological and pathological aspects.

Programmed cell death is a key component of tissue homeostasis, normal development and wide variety of diseases. Conventional view refers to programmed cell death form as caspase-mediated apoptosis while necrosis is considered as an accidental and unwanted cell demise, carried out in a non-regulated manner and caused by extreme conditions. However, accumulating evidences indicate that necrotic cell death can also be a regulated process. The term necroptosis has been introduced to describe a cell death receptor-induced, caspase-independent, highly regulated type of programmed cell death process with morphological resemblance of necrosis. Necroptosis recently has been found to contribute to a wide range of pathologic cell death forms including ischemic brain injury, neurodegenerative diseases and viral infection, therefore a better understanding of the necroptotic signaling machinery has clinical relevance.

Regulation of malignant phenotype and bioenergetics by a π-electron donor-inducible mitochondrial MgATPase.

The recognition of poly ADP-ribose transferase-1 (PARP-1) as an ATP sensor receiving this energy source by way of a specific adenylate kinase ATP wire (AK) from mitochondrial ATP synthase (F0F1), and directly regulating cellular mRNA and DNA synthesis, was the first step towards the identification of an effect by PARP-1 that is of fundamental significance. The molecular target of AK-ATP is Arg 34 of the Zn finger I of PARP-1, which is also a site for cation-π interactions as a target of π-electron donors. We now identify this π-electron receptor site as the second active center of PARP-1 which by interaction with a π-electron donor-inducible MgATPase reversibly controls a malignant vs. non-malignant phenotype through energizing the NADH➝NADP+ transhydrogenase, a reaction which is the metabolic connection of PARP-1 to cell function. The specific enzyme-inducing action of the π-electrons is executed by the PARP-1 -topoisomerase I - DNA complex of the nuclei regulating both the nature and the quantity of cellular enzymes that constitute cell-specific physiology.

Dependence of trans-ADP-ribosylation and nuclear glycolysis on the Arg 34-ATP complex of Zn2+ finger I of poly-ADP-ribose polymerase-1.

The H-bonded complex of ATP with Arg 34 of Zn2+ finger I of poly-ADP-ribose polymerase-1 (PARP-1) determines trans-oligo-ADP-ribosylation from NAD+ to proteins other than PARP-1. This mechanism was tested in lysolecithin fractions of non-malignant and cancer cells separately and after their recombination. Cellular PARP-1 activity was recovered when the centrifugal sediment was recombined with the supernatant fraction containing cellular ADP-ribose oligomer acceptor proteins. Combination of the matrix fraction (Mx) of cancer cells (lacking OXPHOS) with its supernatant had the same PARP-1 activity as the Mx alone. The supernatant of non-malignant cells was replaced by glycolytic enzymes as ADP-ribose acceptor. The hexokinase activity of the supernatant increased when OXPHOS of intact cells was uncoupled by carbonyl cyanide 4-(trifluoro methoxy) phenylhydrazone. trans-ADP-ribosylation was demonstrated by polyacrylamide gel electrophoresis.

Identification of poly(ADP-ribose) polymerase-1 as the OXPHOS-generated ATP sensor of nuclei of animal cells.

Our results show that in the intact normal animal cell mitochondrial ATP is directly connected to nuclear PARP-1 by way of a specific adenylate kinase enzymatic path. This mechanism is demonstrated in two models: (a) by its inhibition with a specific inhibitor of adenylate kinase, and (b) by disruption of ATP synthesis through uncoupling of OXPHOS. In each instance the de-inhibited PARP-1 is quantitatively determined by enzyme kinetics. The nuclear binding site of PARP-1 is Topo I, and is identified as a critical "switchpoint" indicating the nuclear element that connects OXPHOS with mRNA synthesis in real time. The mitochondrial-nuclear PARP-1 pathway is not operative in cancer cells.

Quantitative correlation between cellular proliferation and nuclear poly (ADP-ribose) polymerase (PARP-1).

Treatment of cells with lysophosphatidyl choline and centrifugal extraction can separate poly (ADP-ribose) synthetase (PARP-1) and DNA synthetase activities, permitting the experimental analysis and comparison of both multienzyme systems. Only PARP-1 is being assayed by our system. Ca(2+) and Mg(2+) have minor activating effects, and added histones are without activating action. Short end-blocked dsDNAs at nM concentrations and spermine at mM concentrations are maximally activating coenzymes of poly (ADP-ribose) synthesis. Comparison of non-proliferating non-malignant cells with rapidly growing cancer cells demonstrates that rates of poly (ADP-ribose) synthesis and DNA synthesis are highest in pre-confluent non-malignant cells and in proliferating cancer cells, and lowest in contact-inhibited non-malignant cells. Rates of poly (ADP-ribose) synthesis correlate with the number of enzymatically activable PARP-1 molecules per cell, determined under Vmax conditions where activity is linearly proportional to enzyme protein. Contact-inhibited non-malignant cells exhibit only trans-ADP-ribosylation that is not affected by ATP, while rapid growth, especially in cancer cells, demonstrates extensive auto-poly (ADP)-ribosylation that is strongly inhibited by ATP at concentrations present in cells exhibiting normal bioenergetics. Rates of mRNA synthesis in non-proliferating non-malignant cells and in cancer cells were indistinguishable, indicating that the differences observed between cellular phenotypes are most likely due to reassembly of PARP-1 molecules in nuclei to homo-dimers (in cancer cells) and hetero-dimers (in non-cancer cells). A specific inhibitor and an inactivator of PARP-1 each inhibit DNA synthesis when intact cancer cells are pretreated with these drugs. Direct addition of these drugs to permeabilized cells performing DNA synthesis has no effect on DNA synthesis. The most striking diagnostic signal for cancer cells is activation of PARP-1 and of DNA synthesis.

The influence of ATP on poly(ADP-ribose) metabolism.

ATP affects poly(ADP-ribose) metabolism at two distinct sites: it inhibits poly(ADP-ribose) polymerase-1 and activates the glycohydrolase directly. The inhibitory site of ATP on poly(ADP-ribose) polymerase-1 was identified by amino acid exchange mutation to be at the arginine 34 residue in the first Zn2+ finger. Mutation of 138 arginine residue of Zn2+ finger 2 had negligible influence on the inhibitory action of ATP, pinpointing arginine 34 of the first Zn2+ finger as the specific ATP site. The glycohydrolase protein was activated by ATP when the substrate was a long-chain ADP-ribose polymer, but not with a short-chain substrate. Isolated cell nuclei also responded to both inhibition of poly(ADP-ribose) polymerase by ATP and to poly(ADP-ribose) glycohydrolase activation by ATP, demonstrating that enzymological results can be extrapolated to cellular systems. The activation of poly(ADP-ribose) polymerase in nuclei by an alkylating drug was completely suppressed by ATP, demonstrating that the bioenergetic competence of cells can regulate the cytocidal action of DNA alkylating drugs. The potential significance of bioenergetic regulation of poly(ADP-ribose) metabolism is proposed.

Activation of deoxycytidine kinase by deoxyadenosine: implications in deoxyadenosine-mediated cytotoxicity.

The inborn deficiency of adenosine deaminase is characterised by accumulation of excess amounts of cytotoxic deoxyadenine nucleotides in lymphocytes. Formation of dATP requires phosphorylation of deoxyadenosine by deoxycytidine kinase (dCK), the main nucleoside salvage enzyme in lymphoid cells. Activation of dCK by a number of genotoxic agents including 2-chlorodeoxyadenosine, a deamination-resistant deoxyadenosine analogue, was found previously. Here, we show that deoxyadenosine itself is also a potent activator of dCK if its deamination was prevented by the adenosine deaminase inhibitor deoxycoformycin. In contrast, deoxycytidine was found to prevent stimulation of dCK by various drugs. The activated form of dCK was more resistant to tryptic digestion, indicating that dCK undergoes a substrate-independent conformational change upon activation. Elevated dCK activities were accompanied by decreased pyrimidine nucleotide levels whereas cytotoxic dATP pools were selectively enhanced. dCK activity was found to be downregulated by growth factor and MAP kinase signalling, providing a potential tool to slow the rate of dATP accumulation in adenosine deaminase deficiency.

Mechanisms of antitumor action of methyl-3,5-diiodo-4-(4'-methoxyphenoxy)benzoate: drug-induced protein dephosphorylations and inhibition of the permissive action of ceramide on growth factor induced cell proliferation.

The tumoricidal mechanism of methyl-3,5-diiodo-4-(4'-methoxypropoxy)benzoate (DIME), or DIPE, has been analyzed beyond its first recognized cellular site, which is the inhibition of tubulin polymerization. DIME (or DIPE) pretreatment of Eras cells for 3 days abolished ceramide basic fibroblast growth factor (bFGF)-induced glycolysis, coinciding with a block produced by the phosphoprotein dephosphorylation of cdc 25 by protein phosphatase 2A (PP2A). Protein dephosphorylation is directly activated by DIME (or DIPE), and enzyme activities that are dependent on P-proteins are significantly down-regulated (e.g. Topo I and II, MAP-kinase, and cdc-cyclin kinase). Purified PP2A is one target of activation by DIME (or DIPE), and an alkaline phosphatase isoenzyme is also induced by the drug. It is proposed that the pleiotropic effects of DIME (or DIPE) on cancer cells involve the activation of protein dephosphorylations, as well as inhibition of tubulin polymerization.

Anti-cancer action of 4-iodo-3-nitrobenzamide in combination with buthionine sulfoximine: inactivation of poly(ADP-ribose) polymerase and tumor glycolysis and the appearance of a poly(ADP-ribose) polymerase protease.

E-ras 20 tumorigenic malignant cells and CV-1 non-tumorigenic cells were treated with a drug combination of 4-iodo-3-nitrobenzamide (INO(2)BA) and buthionine sulfoximine (BSO). Growth inhibition of E-ras 20 cells by INO(2)BA was augmented 4-fold when cellular GSH content was diminished by BSO, but the growth rate of CV-1 cells was not affected by the drug combination. Analyses of the intracellular fate of the prodrug INO(2)BA revealed that in E-ras 20 cells about 50% of the intracellular reduced drug was covalently protein-bound, and this binding was dependent upon BSO, whereas in CV-1 cells BSO did not influence protein binding. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified as the protein that covalently binds the reduction product of INO(2)BA, which is 4-iodo-3-nitrosobenzamide. Since only the enzymatically reduced drug INOBA bound covalently to GAPDH, the BSO-dependent covalent protein-drug association indicated an apparent nitro-reductase activity present in E-ras 20 cells, but not in CV-1 cells, explaining the selective toxicity. Covalent binding of INOBA to GAPDH inactivated this enzyme in vitro; INO(2)BA+BSO also inactivated cellular glycolysis in E-ras 20 cells because it provided the precursor to the inhibitory species: INOBA. Another event that occurred in INO(2)BA+BSO-treated E-ras 20 cells was the progressive appearance of a poly(ADP-ribose) polymerase protease. This enzyme was partially purified and characterized by the polypeptide degradation product generated from PARP I, which exhibited a 50kDa mass. This pattern of proteolysis of PARP I is consistent with a drug-induced necrotic cell killing pathway.