Niacin deficiency in rats increases the severity of ethylnitrosourea-induced anemia and leukopenia

Many chemotherapeutic agents function by damaging the DNA of rapidly dividing cells, leading to side effects in the bone marrow, including anemia and leukopenia during chemotherapy and the development of secondary leukemias in the years following recovery from the original disease. We have created an animal model of alkylation-based chemotherapy, in nontumor-bearing rats, to investigate the effect of niacin deficiency on the side effects of chemotherapy [2 x 2 design, niacin-deficient (ND) vs. pair-fed (PF) control, and ethylnitrosourea (ENU) vs. vehicle control (C)]. Weanling Long-Evans rats were fed ND diet or PF niacin replete diet for 4 wk. ENU or C treatment started after 1 wk of feeding and consisted of 12 doses delivered by gavage, every other day. At 4 wk postweaning, niacin deficiency and ENU treatment ended, the rats were fed a high-quality control diet (AIN-93M) and the recovery of blood variables was monitored. ND alone decreased growth rate and caused anemia and neutrophilia. ENU treatment alone caused anemia, lymphopenia, neutropenia and an increase in circulating reticulocytes. In combination, ND and ENU treatment synergistically decreased hematocrit. ND prevented the ENU-induced increase in reticulocyte numbers observed in control rats. ND also increased the severity of ENU-induced lymphopenia. A combination of ND and ENU abolished the neutrophilia caused by ND alone. In summary, ND significantly increased the susceptibility of young Long-Evans rats to ENU-induced bone marrow suppression, suggesting that niacin-deficient cancer patients may benefit from supplementation.

Cleavage of automodified poly(ADP-ribose) polymerase during apoptosis. Evidence for involvement of caspase-7

The abundant nuclear enzyme poly(ADP-ribose) polymerase (PARP) synthesizes poly(ADP-ribose) in response to DNA strand breaks. During almost all forms of apoptosis, PARP is cleaved by caspases, suggesting the crucial role of its inactivation. A few studies have also reported a stimulation of PARP during apoptosis. However, the role of PARP stimulation and cleavage during this cell death process remains poorly understood. Here, we measured the stimulation of endogenous poly(ADP-ribose) synthesis during VP-16-induced apoptosis in HL60 cells and found that PARP was cleaved by caspases at the time of its poly(ADP-ribosyl)ation. In vitro experiments showed that PARP cleavage by caspase-7, but not by caspase-3, was stimulated by its automodification by long and branched poly(ADP-ribose). Consistently, caspase-7 exhibited an affinity for poly(ADP-ribose), whereas caspase-3 did not. In addition, caspase-7 was activated and accumulated in the nucleus of HL60 cells in response to the VP-16 treatment. Furthermore, caspase-7 activation was concommitant with PARP cleavage in the caspase-3-deficient cell line MCF-7 in response to staurosporine treatment. These results strongly suggest that, in vivo, it is caspase-7 that is responsible for PARP cleavage and that poly(ADP-ribosyl)ation of PARP accelerates its proteolysis. Cleavage of the active form of caspase substrates could be a general feature of the apoptotic process, ensuring the rapid inactivation of stress signaling proteins.

Preferential perinuclear localization of poly(ADP-ribose) glycohydrolase

The transient nature of poly(ADP-ribosyl)ation, a posttranslational modification of nuclear proteins, is achieved by the enzyme poly(ADP-ribose) glycohydrolase (PARG) which hydrolyzes the poly(ADP-ribose) polymer into free ADP-ribose residues. To investigate the molecular size and localization of PARG, we developed a specific polyclonal antibody directed against the bovine PARG carboxy-terminal region. We found that PARG purified from bovine thymus was recognized as a 59-kDa protein, while Western blot analysis of total cell extracts revealed the presence of a unique 110-kDa protein. This 110-kDa PARG was mostly found in postnuclear extracts, whereas it was barely detectable in the nuclear fractions of COS7 cells. Further analysis by immunofluorescence revealed a cytoplasmic perinuclear distribution of PARG in COS7 cells overexpressing the bovine PARG cDNA. These results provide direct evidence that PARG is primarily a cytoplasmic enzyme and suggest that a very low amount of intranuclear PARG is required for poly(ADP-ribose) turnover.

Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.

Poly(ADP-ribosylation) and apoptosis

Poly(ADP-ribosylation) is a post-translational modification playing a relevant role in DNA damage recovery, DNA replication and viral integration. Several reports also suggest a modulation of this process during cell death by apoptosis. The aim of this review is to discuss the possible involvement of poly(ADP-ribosylation) during apoptosis, by dealing with general considerations on apoptosis, and further examining the correlation between NAD consumption and cell death, the regulation of poly(ADP-ribose) metabolism in apoptotic cells, the effect of poly(ADP-ribose) polymerase inhibition on cell death occurrence and the use of enzyme cleavage as a marker of apoptosis. Finally, the future prospects of the research in this area will be addressed.

Immunological determination and size characterization of poly(ADP-ribose) synthesized in vitro and in vivo

Poly(ADP-ribose) polymerase is a DNA break detecting enzyme playing a role in the surveillance of genome integrity. Poly(ADP-ribose) is synthesized rapidly and transiently from beta-NAD in response to DNA damaging agents. In order to study the physiological significance of poly(ADP-ribose) metabolism, we have developed immunological methods which enable us to study endogenous poly(ADP-ribose) without interfering with cell metabolism and integrity. For this purpose, we produced a highly specific polyclonal anti-poly(ADP-ribose) antibody which immunoreacts with polymers and oligomers. In addition to the immunodot blot method recently described by us (Affar et al., Anal. Biochem. 259 (1998) 280-283), other applications were investigated in cells: (i) detection of poly(ADP-ribose) by ELISA; (ii) characterization of poly(ADP-ribose) size using high resolution gel electrophoresis of polymers, followed by its transfer onto a positively charged membrane and detection with anti-poly(ADP-ribose) antibody; (iii) immunocytochemistry and flow cytometry analyses allowing poly(ADP-ribose) study at the level of individual cells.

Cytochrome P450 CYP1A1 enzyme activity and DNA adducts in placenta of women environmentally exposed to organochlorines

Organochlorine compounds bioaccumulate in fishing and hunting products included in the daily diet of many coastal populations. Prenatal and perinatal exposure to large doses of PCBs and PCDFs was shown to be deleterious on fetal and neonatal development, but information is scarce regarding possible effects of chronic low-dose exposure. This study investigates biomarkers of early effects in newborns from women exposed to organochlorines through the consumption of species from marine food chains, in two remote coastal regions of the province of Quebec (Canada). A CYP1A1-dependent enzyme activity (EROD) and DNA adducts were measured in placenta samples obtained from 30 women living on the Lower-North-Shore of the St. Lawrence River and 22 Inuit women from Nunavik (Arctic Quebec). These biomarkers were also assessed in 30 women from a Quebec urban center (Sept-Iles) as a reference group. Prenatal organochlorine exposure was determined by measuring these compounds in umbilical cord plasma. The amount of bulky polycyclic aromatic hydrocarbon (PAH)-related DNA adducts was significantly greater in the Lower-North-Shore group than in the reference group. Placental EROD activity and the amount of less bulky (OC-related) DNA adducts were significantly higher in the Nunavik group than in the reference group. For both biomarkers, smoking was found to be an important confounding factor. Organochlorine exposure was significantly associated with EROD activity and DNA adduct levels when stratifying for smoking. This study confirms that CYP1A1 enzyme induction and DNA adducts in placental tissue constitute useful biomarkers of early effects induced by environmental exposure to organochlorines.

Liver poly(ADP-ribose)polymerase is resistant to cleavage by caspases

In hepatocytes the DNA repair enzyme poly(ADP-ribose)polymerase (PARP) is not proteolytically cleaved during apoptosis. The reason for this was investigated using a cell-free system that consisted of isolated nuclei from hepatocytes or thymocytes and cytosolic extracts from hepatocytes or thymocytes undergoing apoptosis. It was found that liver PARP is resistant to proteolytic cleavage by the caspases present in the cytosolic extracts. Furthermore, liver PARP was not cleaved by recombinant human caspase-3. It is concluded that PARP proteolysis cannot be used as a marker for hepatocyte apoptosis.

Niacin deficiency increases the sensitivity of rats to the short and long term effects of ethylnitrosourea treatment

Most chemotherapy agents function by causing damage to the DNA of rapidly dividing cells, such as those in the bone marrow, leading to anemia and leukopenia during chemotherapy and the development of secondary leukemias in the years following recovery from the original disease. We created an animal model of nitrosourea-based chemotherapy using ethylnitrosourea (ENU) to investigate the effect of niacin deficiency on the side effects of chemotherapy. Weanling Long-Evans rats were fed diets containing various levels of niacin for a period of 4 weeks. ENU treatment started after 1 week of feeding and consisted of 12 doses delivered by gavage, every other day. Cancer incidence was also monitored in the following months. ENU treatment caused many of the acute symptoms seen in human chemotherapy patients, including anemia and neutropenia. Niacin deficiency (ND) had several interesting effects, alone and in combination with ENU. Niacin deficiency alone caused a modest anemia, while in combination with ENU it induced a severe anemia. Niacin deficiency alone caused a 4-fold increase in circulating neutrophil numbers, and this population was drastically reduced by ENU-treatment. In the long term, macin deficiency caused an increased incidence of cancer, especially chronic granulocytic leukemias.

Poly(ADP-ribose) turnover in quail myoblast cells: relation between the polymer level and its catabolism by glycohydrolase

The concerted action of poly(ADP-ribose) polymerase (PARP) which synthesizes the poly(ADP-ribose) (pADPr) in response to DNA strand breaks and the catabolic enzyme poly(ADP-ribose) glycohydrolase (PARG) determine the level of polymer and the rate of its turnover. In the present study, we have shown that the quail myoblast cells have high levels of basal polymer as compared to the murine C3H10T1/2 fibroblasts. We have conducted this study to investigate how such differences influence polymer synthesis and its catabolism in the cells in response to DNA damage by alkylating agent. In quail myoblast cells, the presence of high MNNG concentration such as 200 microM for 30 min induced a marginal decrease of 15% in the NAD content. For C3H10T1/2 cell line, 64 microM MNNG provoked a depletion of NAD content by approximately 50%. The induction of the polymer synthesis in response to MNNG treatment was 6-fold higher in C3H10T1/2 cells than in quail myoblast cells notwithstanding the fact that 3-fold higher MNNG concentration was used for quail cells. The polymer synthesis thus induced in quail myoblast cells had a 4-5 fold longer half life than those induced in C3H10T1/2 cells. To account for the slow turnover of the polymer in the quail myoblast cells, we compared the activities of the polymer catabolizing enzyme (PARG) in the two cell types. The quail myoblast cells had about 25% less activity of PARG than the murine cells. This difference in activity is not sufficient to explain the large difference of the rate of catabolism between the two cell types implicating other cellular mechanisms in the regulation of pADPr turnover.

Caspase-mediated cleavage of DNA topoisomerase I at unconventional sites during apoptosis

Previous studies have demonstrated that topoisomerase I is cleaved late during apoptosis, but have not identified the proteases responsible or examined the functional consequences of this cleavage. Here, we have shown that treatment of purified topoisomerase I with caspase-3 resulted in cleavage at DDVD146 downward arrowY and EEED170 downward arrowG, whereas treatment with caspase-6 resulted in cleavage at PEDD123 downward arrowG and EEED170 downward arrowG. After treatment of Jurkat T lymphocytic leukemia cells with anti-Fas antibody or A549 lung cancer cells with topotecan, etoposide, or paclitaxel, the topoisomerase I fragment comigrated with the product that resulted from caspase-3 cleavage at DDVD146 downward arrowY. In contrast, two discrete topoisomerase I fragments that appeared to result from cleavage at DDVD146 downward arrowY and EEED170 downward arrowG were observed after treatment of MDA-MB-468 breast cancer cells with paclitaxel. Topoisomerase I cleavage did not occur in apoptotic MCF-7 cells, which lack caspase-3. Cell fractionation and band depletion studies with the topoisomerase I poison topotecan revealed that the topoisomerase I fragment remains in proximity to the chromatin and retains the ability to bind to and cleave DNA. These observations indicate that topoisomerase I is a substrate of caspase-3 and possibly caspase-6, but is cleaved at sequences that differ from those ordinarily preferred by these enzymes, thereby providing a potential explanation why topoisomerase I cleavage lags behind that of classical caspase substrates such as poly(ADP-ribose) polymerase and lamin B1.

Relative affinities of poly(ADP-ribose) polymerase and DNA-dependent protein kinase for DNA strand interruptions

Poly(ADP-ribose) polymerase (PARP) and DNA-dependent protein kinase (DNA-PK) are important nuclear enzymes that cooperate to minimize genomic damage caused by DNA strand interruptions. DNA strand interruptions trigger the ADP-ribosylation activity and phosphorylation activity of PARP and DNA-PK respectively. In order to understand the relationship of PARP and DNA-PK with respect to DNA binding required for their activation, we analyzed the kinetics of the reactions and determined the apparent dissociation constants (Kd app) of the enzymes for DNA strand interruptions. PARP has a high binding affinity for blunt ends of DNA (Kd app=116 pM) and 3' single-base overhangs (Kd app=332 pM) in comparison to long overhangs (Kd app=2.6-5.0 nM). Nicks are good activators of PARP although the affinity of PARP for nicks (Kd app=467 pM) is 4-fold less than that for blunt ends. The Kd app of DNA-PK for 3' single-base overhangs, blunt ends and long overhangs is 704 pM, 1.3 nM and 1.4-2.2 nM respectively. These results demonstrate that (1) PARP, when compared to DNA-PK, has a greater preference for blunt ends and 3' single-base overhangs but a weaker preference for long overhangs, and (2) nicks are effective in attracting and activating PARP. The possible implications of the preferences of PARP and DNA-PK for DNA strand interruptions in vivo are discussed.

Poly(ADP-ribose) glycohydrolase is present and active in mammalian cells as a 110-kDa protein

Poly(ADP-ribose) glycohydrolase (PARG) is the major enzyme responsible for the catabolism of poly(ADP-ribose), a reversible covalent-modifier of chromosomal proteins. Purification of PARG from many tissues revealed heterogeneity in activity and structure of this enzyme. To investigate PARG structure and localization, we developed a highly sensitive one-dimensional zymogram allowing us to analyze PARG activity in crude extracts of Cos-7, Jurkat, HL-60, and Molt-3 cells. In all extracts, a single PARG activity band corresponding to a protein of about 110 kDa was detected. This 110-kDa PARG activity was found mainly in cytoplasmic rather than in nuclear extracts of Cos-7 cells.

Fanconi anemia C protein acts at a switch between apoptosis and necrosis in mitomycin C-induced cell death

Deregulation of apoptosis seems to be a hallmark of the Fanconi anemia (FA) syndrome. In order to further define the role of the FA protein from complementation group C (FAC) in apoptosis, we characterized parameters modified during the mitomycin-C (MMC)-induced apoptotic program. It is shown that despite a higher level of cell death for FA compared to normal lymphoblasts after MMC treatment, FA cells do not display a marked DNA fragmentation. Furthermore, while playing a central role in MMC apoptosis of normal lymphoblasts, the activity of caspase-3-like proteases is altered in FA cells. Interestingly, the disruption of the mitochondrial transmembrane potential (Deltapsi), an early event that can lead to apoptotic or to necrotic death, is accomplished similarly in FA and in normal cells. Finally, it is shown that the overexpressed FAC protein inhibited the apoptotic steps, with the exception of the decrease of the Deltapsi. Altogether, our results indicate that the FAC protein acts at a step preceding the activation of the caspases and after the modification of the Deltapsi, a decision point at which cells can be pushed toward either apoptosis or necrosis and which, consequently, regulates the balance between the two modes of cell death.

Activation of cysteine proteases in cowpea plants during the hypersensitive response--a form of programmed cell death

There is increasing evidence that the hypersensitive response during plant-pathogen interactions is a form of programmed cell death. In an attempt to understand the biochemical nature of this form of programmed cell death in the cowpea-cowpea rust fungus system, proteolytic activity in extracts of fungus-infected and uninfected cowpea plants was investigated, using exogenously added poly(ADP-ribose) polymerase as a marker. Unlike the proteolytic cleavage pattern of endogenous poly(ADP-ribose) polymerase in apoptotic animal cells, exogenously added poly(ADP-ribose) polymerase in extracts of fungus-infected plants was proteolytically cleaved into fragments of molecular masses 77, 52, 47, and 45 kDa. In vitro and in vivo protease inhibitor experiments revealed the activation of cysteine proteases, and possibly a regulatory role, during the hypersensitive response.

Rapid detection of poly(ADP-ribose) polymerase by enzyme-linked immunosorbent assay during its purification and improvement of its purification

We report a new detection method for the purification of poly(ADP-ribose) polymerase (PARP). PARP purification generates many fractions in which PARP is usually detected by a time consuming activity assay. The development of a new method was also needed in order to decrease the utilization of radioactivity. This new method, based on an enzyme-linked immunosorbent assay (ELISA), is very rapid, sensitive, and avoids most radioactivity. Moreover, to illustrate this method, a new matrix was used, the Heparin Sepharose. This matrix was chosen for its affinity for the DNA binding proteins and because it allows the separation of whole PARP from its proteolytic fragments.

Isolation, purification and partial characterization of chloragocytes from the earthworm species Lumbricus terrestris

Chloragocytes were isolated from the earthworm species Lumbricus terrestris. After mechanical dissociation and sedimentation through Percoll, a highly purified fraction of viable chloragocytes was obtained. The isolated chloragocytes accumulated the vital dye neutral red and reduced the tetrazolium dye MTT, thereby indicating cellular integrity. Time of flight flow cytometric analyses revealed a main population of large and highly granulated cells in the 30-33 microm size range. Hydrolase measurements showed that beta-D-N-acetyl-glucosaminidase and acid phosphatase exhibited the highest activities (146.6 and 24.9 mU/mg of protein, respectively), possibly indicating a major role for these 2 hydrolases in the physiological function of chloragocytes. In contrast, other acid hydrolases such as beta-D-galactosidase and beta-D-glucuronidase had specific activities of respectively 26 and 182 times lower than the glucosaminidase. The specific activity of the membrane-bound alkaline phosphatase was comparable to that of its acid counterpart (18.9 vs. 24.9 mU/mg of protein, respectively) and this level of activity may show an important trans-membrane activity in chloragocytes. The cytoplasmic and mitochondrial enzyme isocitrate dehydrogenase had a level of activity comparable to that of the exclusively cytoplasmic enzyme lactate dehydrogenase (6.6 vs. 8.1 mIU/mg of protein, respectively). When L. terrestris chloragocyte homogenates were separated on Percoll, results showed that hydrolases and dehydrogenases were mainly associated with the lighter materials that remained above the Percoll layer. Nonetheless, the detection of significant proportions (15-25%) of the total recovered activity of acid phosphatase and beta-galactosidase in the enriched chloragosome fraction supports the notion that some chloragosomes may be 'lysosome-like' organelles.

Proteolysis of poly(ADP-ribose) polymerase by caspase 3: kinetics of cleavage of mono(ADP-ribosyl)ated and DNA-bound substrates

Poly(ADP-ribose) polymerase (PARP) is an abundant nuclear enzyme which is responsible for synthesis of poly(ADP-ribose) in response to DNA damage caused by numerous agents and during DNA base excision repair. After DNA damage, the enzyme binds to nicks in DNA through its N-terminal zinc fingers and catalyzes the formation of poly(ADP-ribose) on various nuclear acceptors including itself. When DNA damage is extensive, cells induce their own demise by activating the proteases that induce apoptosis (caspases) which cleave PARP and other death substrates. Here we report the development of a new approach to investigate the sensitivity of mono(ADP-ribosyl)ated and DNA-bound PARP to cleavage during apoptosis. The development of a stoichiometric labeling procedure of the enzyme has allowed us to evaluate the catalytic properties of caspase 3 toward mono(ADP-ribosyl)ated PARP at various enzyme:substrate molar ratios. We show that low levels of automodification (< or = 3 U of ADP-ribose per chain) do not inhibit the proteolysis of the substrate. In addition, we demonstrate that binding of unmodified PARP to DNA influences the kinetics of its cleavage by caspase 3.

A nuclear factor other than Sp1 binds the GC-rich promoter of the gene encoding rat poly(ADP-ribose) polymerase in vitro

Poly(ADP-ribose) polymerase is a nuclear enzyme that has been shown to exert a key role in many important cellular functions, including DNA repair. Its activity was shown to vary substantially between tissues; the testis and the thymus expressed the highest levels of PARP whereas the liver and the kidney (as well as a few other tissues) expressed only low levels of PARP proteins in vivo. The GC-rich nature of its upstream gene promoter, along with the lack of TATA and CAAT boxes, a feature common to most housekeeping genes, is consistent with a major regulatory function played by the positive transcription factor Sp1 in rat PARP gene transcription. Sp1 was indeed recently shown to interact with five distinct GC or GT boxes present in the rat PARP promoter. However, the observation that PARP activity was lower in rat liver than in other tissues was shown not to be the result of reduced Sp1 activity in liver cells but rather suggests the interplay of nuclear proteins other than Sp1 that are required to restrict PARP expression in this organ and maybe in others (such as the kidney). In this study, we investigated this possibility further by defining whether other nuclear proteins might bind the PARP promoter to modulate its transcription in liver cells. As a result, we identified a nuclear factor distinct from Sp1 that binds the PARP promoter at a site overlapping the F2 Sp1 element previously identified. Our results suggest that this protein likely belongs to the CTF-NF1 family of transcription factors.

Glycol ethers induce death and necrosis in human leukemia cells

Ethylene glycol ethers are common solvents. Some isomers are toxic for the reproduction and immunity functions of humans and laboratory animals and are antileukemic for rodents. The health hazards of ethylene glycol ethers may result from their ability to induce cell death in various organs or tissues. To study this possibility, the human leukemia cell lines HL-60, Molt3, and K562 were treated with ethylene glycol ethers. 2-Ethoxyethanol and 2-butoxyethanol were selected because they are among the most commonly used ethelyne glycol ethers, but little is known about their individual toxicity. Cell death was detected by trypan blue uptake, flow cytometry, DNA electrophoresis, and poly(ADP-ribose) polymerase proteolysis. The treatments lasted up to 72 h with doses ranging from 1 to 20 mM, which are high relative to the concentrations found in biological fluids of exposed workers. The highest dose of 2-butoxyethanol (20 mM) induced apoptosis in Molt3 cells after 72 h incubation. Other treatments had no effect, induced necrosis, or blocked the cells in the G1 phase of the cell cycle.

Characterization of antibodies specific for the caspase cleavage site on poly(ADP-ribose) polymerase: specific detection of apoptotic fragments and mapping of the necrotic fragments of poly(ADP-ribose) polymerase

Intracellular cysteine proteases are important mediators of apoptosis. Indeed, some nuclear proteins and enzymes are cleaved during apoptosis, in particular poly(ADP-ribose) polymerase (PARP), which is activated by DNA strand interruptions and is involved in DNA repair. PARP is cleaved into two fragments of 29 and 85 kDa (apparent molecular mass) in human promyelomonocytic leukemia cells, HL-60, treated with etoposide to induce apoptosis. These cells possess protease activities, caspases, that share many features with the ICE/CED-3 family. The cleavage occurs between Asp-214 and Gly-215, a site that is conserved in human, bovine, and chicken PARP. This cleavage has been shown to be an early marker of apoptosis. To monitor apoptosis, to understand the role of PARP cleavage by caspases, and to study the role of the two fragments in DNA repair, members of our laboratory have developed two polyclonal antipeptide antibodies directed against the two human PARP sequences: [196-214] for LP96-22 and [215-228] for LP96-24. Moreover, these antibodies will be useful to map the necrotic cleavage of PARP, which generates fragments different from those obtained during apoptosis, and thus to discriminate between apoptotic and necrotic cell death.

Role of an acidic compartment in tumor-necrosis-factor-alpha-induced production of ceramide, activation of caspase-3 and apoptosis

Tumor necrosis factor-alpha (TNF-alpha) apoptosis by recruiting a complex of cytosolic proteins at its plasma membrane receptor. Among them is caspase-8, an interleukin-1beta-converting enzyme (ICE)-like protease that initiates an amplified protease cascade to activate the cell-death machinery. The latter comprises at least caspase-3 and caspase-7, which execute cell death by cleaving numerous protein substrates, including poly(ADP-ribose) polymerase. In addition, TNF-alpha stimulates the production of ceramide, which also activates the death machinery. Whether the signaling pathways elicited by caspase-8 and ceramide proceed independently or intersect at a specific subcellular site is unknown. Using the lysosomotropic agent NH4Cl and the vesicularization inhibitor brefeldin A, we show here the convergence of TNF-alpha-induced death signaling on an acidic, subcellular compartment reminiscent of lysosomes. This compartment generates at least two signaling pathways that account for the caspase-3 activation and apoptosis induced by TNF-alpha, one involving ceramide and caspase-unrelated adapter molecules and another involving yet unknown lysosomal mediators. The apoptosis inhibitor Bcl-2 specifically acts on the ceramide-activated pathway to block caspase-3 activation and apoptosis. The latter result explains why Bcl-2 only partially blocks TNF-alpha-induced apoptosis.

Apparent cleavage of poly(ADP-ribose) polymerase in non-apoptotic mouse LTA cells: an artifact of cross-reactive secondary antibody

Proteolytic cleavage of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) to fragments of 89 kD and 24 kD is widely observed during apoptotic cell death. In the present study, labelling of a Mr approximately 89000 polypeptide was demonstrated in untreated mouse LTA cells during probing of immunoblots with C-2-10 monoclonal anti-PARP antibody. The source of the labeling was traced to the secondary antibody preparation, which labeled a Mr approximately 89000 polypeptide in murine LTA cells but not in human cells. These observations indicate that assessment of PARP cleavage must be (1) performed with appropriate controls when new cell lines are investigated and (2) carefully interpreted in light of additional biochemical or morphological data demonstrating apoptotic changes.

6-Aminonicotinamide sensitizes human tumor cell lines to cisplatin

The nicotinamide analogue 6-aminonicotinamide (6AN) is presently undergoing evaluation as a potential modulator of the action of various antineoplastic treatments. Most previous studies of this agent have focused on a three-drug regimen of chemical modulators that includes 6AN. In the present study, the effect of single-agent 6AN on the efficacy of selected antineoplastic drugs was assessed in vitro. Colony-forming assays using human tumor cell lines demonstrated that pretreatment with 30-250 microM 6AN for 18 h resulted in increased sensitivity to the DNA cross-linking agent cisplatin, with 6-, 11-, and 17-fold decreases in the cisplatin dose that diminishes colony formation by 90% being observed in K562 leukemia cells, A549 non-small cell lung cancer cells, and T98G glioblastoma cells, respectively. Morphological examination revealed increased numbers of apoptotic cells after treatment with 6AN and cisplatin compared to cisplatin alone. 6AN also sensitized cells to melphalan and nitrogen mustard but not to chlorambucil, 4-hydroperoxycyclophosphamide, etoposide, or daunorubicin. In additional studies undertaken to elucidate the mechanism underlying the sensitization to cisplatin, atomic absorption spectroscopy revealed that 6AN had no effect on the rate of removal of platinum (Pt) adducts from DNA. Instead, 6AN treatment was accompanied by an increase in Pt-DNA adducts that paralleled the degree of sensitization. This effect was not attributable to 6AN-induced decreases in glutathione or NAD+, because other agents that depleted these detoxification cofactors (buthionine sulfoximine and 3-acetylpyridine, respectively) did not increase Pt-DNA adducts. On the contrary, 6AN treatment increased cellular accumulation of cisplatin. Further experiments revealed that 6AN was metabolized to 6-aminonicotinamide adenine dinucleotide (6ANAD+). Concurrent administration of nicotinamide and 6AN had minimal effect on cellular 6AN accumulation but abolished the formation of 6ANAD+, the increase in Pt-DNA adducts, and the sensitizing effect of 6AN in clonogenic assays. These observations identify 6AN as a potential modulator of cisplatin sensitivity and suggest that the 6AN metabolite 6ANAD+ exerts this effect by increasing cisplatin accumulation and subsequent formation of Pt-DNA adducts.