c-Abl activation regulates induction of the SEK1/stress-activated protein kinase pathway in the cellular response to 1-beta-D-arabinofuranosylcytosine

Previous work has shown that treatment of cells with the antimetabolite 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with induction of the c-jun gene. The present studies demonstrate that ara-C activates the c-Abl non-receptor tyrosine kinase. We also demonstrate that activity of the stress-activated protein kinase (SAP kinase/JNK) is increased in ara-C-treated cells. Using cells deficient in c-Abl (Abl-/-) and after introduction of the c-abl gene, we show that ara-C-induced c-Abl activity is necessary for the stimulation of SAP kinase. Other studies using cells transfected with a SEK1 dominant negative demonstrate that ara-C-induced SAP kinase activity is SEK1-dependent. Furthermore, we show that overexpression of truncated c-Abl results in activation of the SEK1/SAP kinase cascade.

Involvement of stress-activated protein kinase in the cellular response to 1-beta-D-arabinofuranosylcytosine and other DNA-damaging agents

The cellular response to 1-beta-D-arabinofuranosylcytosine (ara-C) includes activation of Jun/AP-1, induction of c-jun transcription, and programmed cell death. The stress-activated protein (SAP) kinases stimulate the transactivation function of c-jun by amino terminal phosphorylation. The present work demonstrates that ara-C activates p54 SAP kinase. The finding that SAP kinase is also activated by alkylating agents (mitomycin C and cisplatinum) and the topoisomerase I inhibitor 9-amino-camptothecin supports DNA damage as an initial signal in this cascade. The results demonstrate that ara-C also induces binding of SAP kinase to the SH2/SH3-containing adapter protein Grb2. SAP kinase binds to the SH3 domains of Grb2, while interaction of the p85 alpha-subunit of phosphatidylinositol 3-kinase complex. The results also demonstrate that ara-C treatment is associated with inhibition of lipid and serine kinase activities of PI 3-kinase. The potential significance of the ara-C-induced interaction between SAP kinase and PI 3-kinase is further supported by the demonstration that Wortmannin, an inhibitor of PI 3-kinase, stimulates SAP kinase activity. The finding that Wortmannin treatment is also associated with internucleosomal DNA fragmentation may support a potential link between PI 3-kinase and regulation of both SAP kinase and programmed cell death.

Association of the DF3/MUC1 breast cancer antigen with Grb2 and the Sos/Ras exchange protein

The DF3/MUC1 mucin-like glycoprotein is aberrantly overexpressed in human breast carcinomas. Although the precise functional role of this protein remains unclear, the cytoplasmic tail contains potential tyrosine phosphorylation sites for binding to Src homology 2 (SH2) domains. In the present studies using human MCF-7 breast cancer cells, we show that tyrosine phosphorylated DF3 directly interacts with the SH2 domain of the adaptor protein Grb2. The findings indicate that a pYTNP site in DF3 is responsible for this interaction. The results also demonstrate that the DF3/Grb2 complex associates with the guanine nucleotide exchange protein Sos. Because Sos binds to the SH3 domains of Grb2 and, thereby, associates with Ras at the cell membrane, formation of a DF3/Grb2/Sos complex supports a role for DF3 in intracellular signaling.

Stimulation of human monocytes with macrophage colony-stimulating factor induces a Grb2-mediated association of the focal adhesion kinase pp125FAK and dynamin

Macrophage colony-stimulating factor (M-CSF) is required for the growth and differentiation of mononuclear phagocytes. In the present studies using human monocytes, we show that M-CSF induces interaction of the Grb2 adaptor protein with the focal adhesion kinase pp125FAK. The results demonstrate that tyrosine-phosphorylated pp125FAK directly interacts with the SH2 domain of Grb2. The findings indicate that a pYENV site at Tyr-925 in pp125FAK is responsible for this interaction. We also demonstrate that the Grb2-FAK complex associates with the GTPase dynamin. Dynamin interacts with the SH3 domains of Grb2 and exhibits M-CSF-dependent tyrosine phosphorylation in association with pp125FAK. These findings suggest that M-CSF-induced signaling involves independent Grb2-mediated pathways, one leading to Ras activation and another involving pp125FAK and a GTPase implicated in receptor internalization.

Monocyte colony-stimulating factor stimulates binding of phosphatidylinositol 3-kinase to Grb2.Sos complexes in human monocytes

Monocyte colony-stimulating factor (M-CSF) is required for the proliferation of mononuclear phagocytes. The activated M-CSF receptor associates with phosphatidylinositol 3-kinase (PI 3-kinase). In the present studies, we demonstrate that M-CSF also induces direct interaction of PI 3-kinase (p85 alpha subunit) with the SH2/SH3 adaptor protein Grb2. Tyrosine-phosphorylated PI 3-kinase interacts with the SH2 domain of Grb2. A pYRNE (pY408) site in PI 3-kinase is potentially involved in this interaction. The results also demonstrate that the PI 3-kinase.Grb2 complex associates with the guanine nucleotide exchange protein Sos. Since Sos binds to the SH3 domains of Grb2 and thereby associates with Ras at the cell membrane, formation of the PI 3-kinase.Grb2.Sos complex provides a potential mechanism for growth factor-induced interactions of PI 3-kinase and Ras.

Expression of the DF3-P epitope in human ovarian carcinomas

Recent studies have described the generation of a mAb, designated DF3-P, which reacts with underglycosylated precursors of the DF3/MUC1 mucin-like glycoprotein. The present work demonstrates that the epitope recognized by mAb DF3-P is expressed by cell lines derived from human epithelial ovarian carcinomas and not a teratocarcinoma. Indirect immunofluorescence assays of single-cell suspensions support expression of the DF3-P epitope on the surface of ovarian carcinomas. Immunofluorescence studies on chamber slides further demonstrate that the mAb DF3-P-reactive cells are present in clusters. We also demonstrate that 125I-labeled mAb DF3-P selectively localizes to human ovarian carcinoma xenografts in athymic mice. The percentage of injected 125I dose/g tissue ranged between 10 and 17% for implanted CAOV-3 and OVCAR-3 tumors. Finally, the results of immunoperoxidase staining studies demonstrate that the DF3-P epitope is detectable in formalin-fixed sections of ovarian tumors and that mAb DF3-P exhibits little if any reactivity with normal surrounding tissues. Selective expression of the DF3-P epitope may be useful as a target for radioimaging or immunotherapeutic approaches to ovarian cancer.

Overexpression of Bcl-XL by cytotoxic drug exposure confers resistance to ionizing radiation-induced internucleosomal DNA fragmentation

Acquired resistance to diverse chemotherapeutic agents has been associated with overexpression of the P-glycoprotein. We have selected human U-937 cells for clones resistant to the cytotoxic agents doxorubicin (U-A20) and vincristine (U-V20). The results demonstrate that P-glycoprotein-positive U-A20 and U-V20 cells exhibit resistance to inducers of internucleosomal DNA fragmentation. Although parental U-937 cells responded to ionizing radiation with the DNA laddering characteristic of physiological cell death, the drug-resistant lines were insensitive to this effect. The U-A20 and U-V20 clones were also resistant to endonucleolytic DNA cleavage associated with exposure to tumor necrosis factor or ceramide. Previous work has demonstrated that physiological cell death is inhibited by overexpression of the Bcl-2 protein. However, analysis of Bcl-2 revealed similar levels in the parental and drug-resistant cells. In contrast, we show that U-A20 and U-V20 cells overexpress the Bcl-2-related protein, Bcl-xL. Moreover, studies with a U-937 cell line transfected with a Bcl-XL expression vector confirm resistance to ionizing radiation-induced DNA fragmentation and cell killing. These findings suggest that, unlike Bcl-2, Bcl-XL may be constitutively overexpressed as a result of selection for cytotoxic drug resistance and that Bcl-XL participates in an acquired form of multimodality resistance to chemotherapeutic agents and radiation.

1-beta-D-arabinofuranosylcytosine activates tyrosine phosphorylation of p34cdc2 and its association with the Src-like p56/p53lyn kinase in human myeloid leukemia cells

Recent studies have demonstrated that treatment of human myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with activation of serine/threonine protein kinases and early response gene expression. The present work has examined the involvement of protein tyrosine phosphorylation in ara-C-induced responses of HL-60 myeloid leukemia cells. The results of immunoprecipitation studies demonstrate that HL-60 cells respond to ara-C with tyrosine phosphorylation of the cell cycle regulatory protein p34cdc2 and a decrease in the activity of this kinase. This effect was detectable at 15 min of ara-C exposure. Coimmunoprecipitations with anti-p34cdc2 support binding of this protein to the Src-like p56/p53lyn tyrosine kinase in ara-C-treated, but not untreated, cells. The results further demonstrate that ara-C treatment is associated with a dose-dependent activation of p56/p53lyn and that ara-C-induced p56/p53lyn activity is blocked by the protein tyrosine inhibitors herbimycin A and genistein. Studies with a glutathione S-transferase-Lyn fusion protein confirm interaction of p34cdc2 and p56/p53lyn in lysates of ara-C-treated cells. Moreover, we demonstrate that (1) p56/p53lyn phosphorylates Tyr-15 of p34cdc2 in vitro and (2) phosphorylation of p34cdc2 by p56/p53lyn inhibits p34cdc2 activity. These findings indicate that the cellular response to ara-C includes activation of p56/p53lyn and that association of p56/p53lyn with p34cdc2 may contribute to regulation of the cell cycle progression in ara-C-treated cells.

p56/p53lyn tyrosine kinase activation in mammalian cells treated with mitomycin C

The present studies have examined the effects of mitomycin C (MMC), a genotoxic alkylating agent, on the activation of Src-like protein tyrosine kinases in HL-60 myeloid leukemia cells. The results demonstrate no detectable induction of p59fyn or pp60c-src activity. The response of HL-60 cells to MMC however was associated with rapid activation of p56/p53lyn. Similar findings were obtained with other alkylating agents such as nitrogen mustard and cis-platinum. Activation of p56/p53lyn was associated with increased autophosphorylation on tyrosine and sensitivity to the tyrosine kinase inhibitors herbimycin A and genistein. Studies with a glutathione S-transferase-Lyn fusion protein were performed to explore the potential significance of p56/p53lyn activation. Analysis of the adsorbates demonstrates interaction of Lyn with the cell cycle regulatory protein, p34cdc2. Coimmunoprecipitation studies further confirmed the association of p56/p53lyn and p34cdc2 in MMC-treated cells. We also demonstrate that p34cdc2 undergoes increased phosphorylation on tyrosine following MMC exposure and that p56/p53lyn phosphorylates the Tyr-15 site of p34cdc2 in vitro. These findings indicate that the cellular response to MMC includes activation of p56/p53lyn and that this event may contribute to signals transduced by the DNA damage-dependent mitotic checkpoint.

Therapy with recombinant human erythropoietin in patients with myelodysplastic syndromes

We conducted a Phase I-II trial of recombinant human erythropoietin-beta (rhEPO) in patients with myelodysplastic syndrome (MDS). Patients with anemia and pathologically confirmed MDS were eligible for the study. Treatment consisted of rhEPO by subcutaneous injection thrice weekly for 6 weeks at one of three dose levels (100 U/kg (three patients), 200 U/kg (three patients) and 400 U/kg (14 patients)). Ferrous sulfate (325 mg po tid) was also administered if the transferrin saturation was below 30% (two patients). Patients were monitored with weekly CBC, white cell differential, and reticulocyte counts. Bone marrow examinations were performed at the conclusion of the treatment period and after a 2 week washout period. Patients who responded to therapy were continued on rhEPO at the same dose for 6 additional months. Response criteria included: 50% reduction in transfusion requirements compared with the 6 week pre-study period; doubling of reticulocyte count that was maintained on two determinations at least 1 week apart; or an increase in hemoglobin by at least 1.2 gm/dl without transfusions. Pre-treatment factors potentially predictive of response were analyzed by univariate analysis and in a multivariate fashion by classification and regression trees. Seven of the twenty patients sustained an untransfused rise in serum hemoglobin > or = 1.2 gm/dl. Four of the sixteen patients (including three of seven patients experiencing a rise in serum hemoglobin) who were transfusion-dependent prior to the study achieved a reduction or elimination of their transfusion requirements. Five of thirteen patients who received rhEPO during the extension phase had a continued response. A low baseline erythropoietin level (< 50 mU/ml) was the best predictor of hemoglobin response when controlling for other variables. rhEPO has a role in the treatment of certain patients with MDS, particularly in those whose endogenous serum erythropoietin levels are not markedly elevated.

Partial characterization of human leukemia U-937 cell sublines resistant to 9-nitrocamptothecin

Human leukemia U-937 cell sublines exhibiting various levels of resistance to 9-nitrocamptothecin (9NC) were developed after exposure to progressively increased 9NC concentrations. Increases in 9NC resistance of the cells were accompanied by decreases in proliferation rate; appearance of morphological and functional features that correlate with granulocytic maturation; decreased synthesis of topoisomerase I; increased synthesis of topoisomerase II; and inability or decreased ability to induce tumors when xenografted in nude mice. 9NC-resistant cells, transferred and propagated in 9NC-free media for 6 months, continue to exhibit resistance and other features similar to cells propagated in continual presence of 9NC. Finally, 9NC-resistant U-937 cells respond to physiological and non-physiological agents of cell differentiation, indicating that alternative treatments can be successfully used to inhibit growth of 9NC-resistant U-937 cells and tumors.

Radiation induction of immediate early genes: effectors of the radiation-stress response

Recent studies have demonstrated that the early response genes c-jun, Egr-1, c-fos, and NF kappa B are induced following exposure of mammalian cells to ionizing radiation. We propose that the products of these early response genes regulate downstream genes that are important in the adaptation of cells and tissues to radiation-induced stress. Potential downstream targets include cytokine and growth factor genes as well as deoxyribonucleic acid (DNA) repair genes. Early response gene products may also regulate cell cycle progression following cellular x-irradiation. Signal transduction pathways that allow cells to adapt to radiation may provide molecular targets to modify tumor and normal responses to radiotherapy.

Activation of Src-like p56/p53lyn tyrosine kinase by ionizing radiation

Mammalian cells respond to ionizing radiation (IR) with cell cycle arrest, activation of DNA repair, and induction of early response genes. The present work has examined the involvement of Src-like protein-tyrosine kinases in the response of irradiated HL-60 myeloid leukemia cells. The results demonstrate little if any effect of IR on p59fyn, p56lck, and pp60c-src activity. In contrast, HL-60 cells responded to x-ray exposure with activation of p56/p53lyn. At a dose of 200 centigrays, induction of p56/p53lyn activity was detectable at 15 min. Doses as low as 50 centigrays were effective in activating p56/p53lyn. H2O2 and the scavenger N-acetylcysteine had no detectable effect on p56/p53lyn activation, while the protein-tyrosine kinase inhibitors, herbimycin and genistein, blocked induction by IR. The results also demonstrate that incubation of a glutathione S-transferase-Lyn fusion protein with lysates of irradiated HL-60 cells is associated with binding of the cell cycle regulatory protein, p34cdc2. The interaction of p56/p53lyn and p34cdc was confirmed in similar experiments with a glutathione S-transferase-Cdc2 fusion protein. Moreover, coimmunoprecipitation studies demonstrate the selective binding of activated p56/p53lyn to p34cdc2 in irradiated cells. These findings indicate that IR activates p56/p53lyn in HL-60 cells and that this tyrosine kinase may contribute to the regulation of p34cdc2.

1-beta-D-arabinofuranosylcytosine activates serine/threonine protein kinases and c-jun gene expression in phorbol ester-resistant myeloid leukemia cells

1-beta-D-Arabinofuranosylcytosine (ara-C) is an effective antileukemic agent that misincorporates into DNA. Recent studies have demonstrated that ara-C treatment is associated with transient induction of the c-jun early response gene. The present studies have examined the effects of ara-C on c-jun expression in a phorbol ester-resistant variant of the HL-60 myeloid leukemia cell line, designated HL-525, that is deficient in protein kinase C (PKC)-mediated signal transduction and fails to respond to 12-O-tetradecanoylphorbol-13-acetate with induction of c-jun transcripts. The results demonstrate that treatment of HL-525 cells with ara-C is associated with transcriptional activation of the c-jun gene. We also demonstrate that ara-C treatment is associated with activation of a PKC-like activity. Partial purification of this Ca(2+)-independent activity has demonstrated phosphorylation of synthetic peptides derived from (a) amino acids 4-14 of myelin basic protein and (b) the pseudosubstrate region of PKC (amino acids 19-31), with substitution of Ala25 with serine. The finding that the ara-C-induced activity is inhibited by the pseudosubstrate PKC(19-36) supports the activation of a PKC-like enzyme. Because PKC can act upstream of the mitogen-activated protein (MAP) kinases, we studied the effects of ara-C treatment on MAP kinase activity. The results demonstrate that MAP kinase is activated in ara-C-treated cells and that the kinetics of this activation are similar to those of the PKC-like activity. Because 12-O-tetradecanoylphorbol-13-acetate has little, if any, effect on the PKC-like and MAP kinase activities in HL-525 cells, these findings suggest that ara-C activates a distinct signaling cascade that may contribute to induction of the c-jun gene.

Activation of the pp90rsk and mitogen-activated serine/threonine protein kinases by ionizing radiation

The cellular response to ionizing radiation (IR) includes induction of the c-jun and EGR1 early response genes. The present work has examined potential cytoplasmic signaling cascades that transduce IR-induced signals to the nucleus. The results demonstrate activation of the 40S ribosomal protein S6 kinase, pp90rsk, in human U-937 myeloid leukemia cells. Partial purification of pp90rsk by affinity chromatography demonstrated an increase in S6 peptide phosphorylation when comparing irradiated with control cells. IR-induced activation of pp90rsk was further confirmed in immune-complex kinase assays. In contrast to these findings, there was no detectable induction of pp70S6K. Previous work has demonstrated that mitogen-activated protein kinase activates pp90rsk. The present results further show that IR treatment is associated with induction of mitogen-activated protein kinase activity and that this event is temporally related to activation of pp90rsk and early response gene expression. These findings suggest that activation of the mitogen-activated protein kinase/pp90rsk cascade is involved in the response of cells to IR exposure.

Ionizing radiation induces rapid tyrosine phosphorylation of p34cdc2

Eukaryotic cells respond to ionizing radiation exposure with cell cycle arrest. However, little is known about the signaling mechanisms responsible for this effect. The present work has asked whether ionizing radiation exposure is associated with changes in phosphorylation of proteins in HL-60 myeloid leukemia cells. The results demonstrate increased tyrosine phosphorylation of a M(r) 34,000 substrate. This effect was detectable at 1 to 10 min after irradiation and was induced by doses of 50 to 500 cGy. Immunoprecipitation studies further suggest that this substrate is the serine/threonine p34cdc2 protein kinase. Since p34cdc2 is required for entry into mitosis, these findings support the posttranslational modification of a cell cycle regulatory protein in the response to ionizing radiation.

Activation of early growth response 1 gene transcription and pp90rsk during induction of monocytic differentiation

The present work has studied mechanisms responsible for induction of early growth response 1 (EGR-1) gene expression during monocytic differentiation of U-937 myeloid leukemia cells. Differentiation of U-937 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of the serine/threonine protein kinase C, was associated with transcriptional activation of EGR-1 promoter-reporter constructs. The EGR-1 promoter contains six CC(A/T)6GG (CArG) motifs. The two 5'-most distal CArG sequences conferred TPA inducibility. In contrast, there was little effect of TPA on EGR-1 transcription in a TPA-resistant U-937 cell variant, designated TUR. Treatment of both U-937 and TUR cells with okadaic acid, an inhibitor of serine/threonine protein phosphatases 1 and 2A, was associated with induction of monocytic differentiation and EGR-1 transcription through the 5'-most CArG element. Since these findings supported the involvement of serine/threonine protein phosphorylation in the regulation of EGR-1 expression, we studied activation of the 40S ribosomal protein S6 serine/threonine kinases, pp70S6K and pp90rsk. Although both kinases participate in regulating cell growth, there was no detectable activation of pp70S6K during TPA- or okadaic acid-induced monocytic differentiation. Moreover, rapamycin, an inhibitor of pp70S6K activation, had no effect on induction of EGR-1 expression. In contrast, analysis of pp90rsk activity by phosphorylation of a peptide derived from S6 protein demonstrated stimulation of this kinase in TPA-treated U-937, and not TUR, cells. Okadaic acid treatment of both cell types was associated with activation of pp90rsk.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a mutant human topoisomerase I with intact catalytic activity and resistance to 9-nitro-camptothecin

Human U-937 myeloid leukemia cells were selected for resistance to increasing concentrations of the camptothecin derivative, 9-nitro-20(S)camptothecin (9-NC). The isolated single cell clone, designated U-937/CR, was approximately 20-fold resistant to 9-NC. Analysis of topoisomerase I (topo I) gene expression in U-937/CR cells demonstrated similar mRNA levels as compared with U-937 cells. Immunoblotting with an anti-topo I serum revealed reactive proteins at 100, 75, and 67 kDa which were expressed at the same level in the parental and 9-NC-resistant clones. These cell lines also demonstrated similar levels of topo I catalytic activity as determined by assaying nuclear extracts for relaxation of supercoiled plasmid DNA. In contrast, catalytic assays performed in the presence of 9-NC demonstrated that topo I activity from U-937/CR cells was approximately 10-fold more resistant than that from U-937 cells. Nucleotide sequencing of topo I cDNAs revealed the substitution of phenylalanine (TTC) at residue 361 in U-937 cells with serine (TCC) in the 9-NC-resistant clone. Expression and partial purification of the mutant topo I protein in Escherichia coli demonstrated resistance of this enzyme to 9-NC in catalytic assays. Taken together, these findings identify a novel mutation in topo I which confers resistance to 9-NC and support the involvement of this region in the interaction between topo I and 9-NC.

Activation of Raf-1 and mitogen-activated protein kinases during monocytic differentiation of human myeloid leukemia cells

Treatment of human myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C (PKC), is associated with induction of monocytic differentiation. Since PKC can act immediately upstream to the cytoplasmic Raf-1 serine/threonine protein kinase, we studied activation of Raf-1 during induction of the differentiated monocytic phenotype. The results demonstrate that Raf-1 is activated during TPA-induced monocytic differentiation of HL-60 cells. In contrast, there was little effect of TPA on this kinase in an HL-60 variant, designated HL-525, which is resistant to TPA-induced differentiation. Treatment of both HL-60 and HL-525 cells with okadaic acid, an inhibitor of serine/threonine protein phosphatases 1 and 2A, was associated with Raf-1 activation and induction of the monocytic phenotype. Since Raf-1 can activate the mitogen-activated protein (MAP) kinases, we also studied the relationship between MAP kinase activation and monocytic differentiation. Treatment of HL-60, but not HL-525, cells with TPA was associated with increased MAP kinase activity as determined by phosphorylation of myelin basic protein and the c-Jun Y peptide. Okadaic acid-induced differentiation of both HL-60 and HL-525 cells was similarly accompanied by increases in MAP kinase activity. These findings indicated that activation of Raf-1/MAP kinase signaling is associated with induction of a differentiated monocytic phenotype and that okadaic acid bypasses a defect in this cascade in TPA-treated HL-525 cells. While recent studies have shown that HL-525 cells are deficient in PKC beta, the present results demonstrate that PKC beta expression is up-regulated in the HL-525 variant by treatment with retinoic acid. The results also demonstrate that retinoic acid-treated HL-525 cells respond to TPA with activation of Raf-1 and MAP kinase, as well as induction of monocytic differentiation. Taken together, the results indicate that activation of Raf-1/MAP kinase signaling is associated with monocytic differentiation and that stimulation of serine/threonine protein phosphorylation by TPA or okadaic acid is sufficient for reversal of the leukemic HL-60 phenotype.

Coinduction of c-jun gene expression and internucleosomal DNA fragmentation by ionizing radiation

Previous work has demonstrated that the cellular response to ionizing radiation includes transcriptional activation of the c-jun early response gene. The present studies demonstrate that this induction of c-jun expression is temporally related to the appearance of internucleosomal DNA fragmentation. These events were maximal at 6 h and transient after exposure to lethal doses (20 Gy) of ionizing radiation. We also demonstrate that N-acetyl-L-cysteine (NAC), an antioxidant, inhibits X-ray-induced c-jun expression and endonucleolytic DNA cleavage. These findings suggested that both events are mediated at least in part through the formation of reactive oxygen intermediates (ROIs). Since ROIs damage DNA and X-ray-induced DNA damage is associated with activation of poly(ADP-ribose) polymerase (ADPRP), we studied the effects of the ADPRP inhibitors 3-aminobenzamide (3-AB), nicotinamide, and theophylline. 3-AB blocked both X-ray-induced c-jun expression and internucleosomal DNA fragmentation. Similar findings were obtained with nicotinamide and theophylline. In contrast, 3-AB had little if any effect on induction of c-jun transcripts or DNA fragmentation induced by the alkylating agent mitomycin C. While c-jun expression is restricted to cells in G1 and G1/S phases, we have found that X-ray-induced c-jun transcripts are detectable throughout all phases of the cell cycle. The induction of internucleosomal DNA fragmentation by X-rays was also detectable throughout the cell cycle. Taken together, these results support the coinduction of c-jun transcription and internucleosomal DNA fragmentation by ionizing radiation. Similar studies were performed with H2O2 since this agent also results in the production of ROIs.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of the early growth response 1 gene and nuclear pp90rsk in human myeloid leukemia cells by 1-(beta-D-arabinofuranosyl)cytosine

The early growth response 1 (EGR-1) gene is induced by mitogens, differentiating stimuli, and certain genotoxic agents in diverse cell types. The present work has examined the effects of 1-(beta-D-arabinofuranosyl)cytosine (ara-C), an antileukemia agent that misincorporates into DNA, on EGR-1 expression. Treatment of HL-525 myeloid leukemia cells with ara-C was associated with transient increases in EGR-1 mRNA levels. Nuclear run-on assays showed that this effect is related at least in part to activation of EGR-1 gene transcription. Sequences responsive to ara-C-induced signals were determined by deletion analysis of the EGR-1 promoter. The results demonstrate that ara-C inducibility of the EGR-1 gene is conferred by a region containing six serum response or CC(A/T)6GG (CArG) motifs. Further analysis demonstrated that the first two distal or 5'-most CArG elements are functional in the ara-C response. An oligomer corresponding to the first CArG element also conferred ara-C inducibility of the minimal thymdine kinase gene promoter, while no inducibility was detectable using a similar oligomer containing a mutated CArG box. Other work has demonstrated that the nuclear serum response factor (SRF) interacts with the CArG box in the EGR-1 promoter and that the serine/threonine pp90rsk protein kinase phosphorylates SRF in vitro at sites phosphorylated in vivo. The present studies demonstrate that ara-C has little if any effect on cytosolic pp90rsk as determined by immunoblotting to assess electrophoretic mobility and by immune-complex kinase assays using S6 peptide as substrate.(ABSTRACT TRUNCATED AT 250 WORDS)