A quantum coherent spin in hexagonal boron nitride at ambient conditions.

Solid-state spin-photon interfaces that combine single-photon generation and long-lived spin coherence with scalable device integration-ideally under ambient conditions-hold great promise for the implementation of quantum networks and sensors. Despite rapid progress reported across several candidate systems, those possessing quantum coherent single spins at room temperature remain extremely rare. Here we report quantum coherent control under ambient conditions of a single-photon-emitting defect spin in a layered van der Waals material, namely, hexagonal boron nitride. We identify that the carbon-related defect has a spin-triplet electronic ground-state manifold. We demonstrate that the spin coherence is predominantly governed by coupling to only a few proximal nuclei and is prolonged by decoupling protocols. Our results serve to introduce a new platform to realize a room-temperature spin qubit coupled to a multiqubit quantum register or quantum sensor with nanoscale sample proximity.

VE-Cadherin in Cancer-Associated Angiogenesis: A Deceptive Strategy of Blood Vessel Formation.

Tumor growth depends on the vascular system, either through the expansion of blood vessels or novel adaptation by tumor cells. One of these novel pathways is vasculogenic mimicry (VM), which is defined as a tumor-provided vascular system apart from endothelial cell-lined vessels, and its origin is partly unknown. It involves highly aggressive tumor cells expressing endothelial cell markers that line the tumor irrigation. VM has been correlated with high tumor grade, cancer cell invasion, cancer cell metastasis, and reduced survival of cancer patients. In this review, we summarize the most relevant studies in the field of angiogenesis and cover the various aspects and functionality of aberrant angiogenesis by tumor cells. We also discuss the intracellular signaling mechanisms involved in the abnormal presence of VE-cadherin (CDH5) and its role in VM formation. Finally, we present the implications for the paradigm of tumor angiogenesis and how targeted therapy and individualized studies can be applied in scientific analysis and clinical settings.

VE-Cadherin modulates ß-catenin/TCF-4 to enhance Vasculogenic Mimicry.

Vasculogenic Mimicry (VM) refers to the capacity to form a blood network from aggressive cancer cells in an independent way of endothelial cells, to provide nutrients and oxygen leading to enhanced microenvironment complexity and treatment failure. In a previous study, we demonstrated that VE-Cadherin and its phosphorylation at Y658 modulated kaiso-dependent gene expression (CCND1 and Wnt 11) through a pathway involving Focal Adhesion kinase (FAK). In the present research, using a proteomic approach, we have found that ß-catenin/TCF-4 is associated with nuclear VE-cadherin and enhances the capacity of malignant melanoma cells to undergo VM in cooperation with VE-Cadherin; in addition, preventing the phosphorylation of Y658 of VE-cadherin upon FAK disabling resulted in VE-Cadherin/ß-catenin complex dissociation, increased ß-catenin degradation while reducing TCF-4-dependent genes transcription (C-Myc and Twist-1). Uveal melanoma cells knockout for VE-Cadherin loses ß-catenin expression while the rescue of VE-Cadherin (but not of the phosphorylation defective VE-Cadherin Y658F mutant) permits stabilization of ß-catenin and tumor growth reduction in vivo experiments. In vivo, the concomitant treatment with the FAK inhibitor PF-271 and the anti-angiogenic agent bevacizumab leads to a strong reduction in tumor growth concerning the single treatment. In conclusion, the anomalous expression of VE-Cadherin in metastatic melanoma cells (from both uveal and cutaneous origins), together with its permanent phosphorylation at Y658, favors the induction of the aggressive VM phenotype through the cooperation of ß-catenin with VE-Cadherin and by enhancing TCF-4 genes-dependent transcription.

Glioblastoma Cells Counteract PARP Inhibition through Pro-Survival Induction of Lipid Droplets Synthesis and Utilization.

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. Poly (ADP-ribose) polymerase inhibitors (PARPi) represent a new class of anti-neoplastic drugs. In the current study, we have characterized the mechanism by which glioblastoma cells evade the effect of PARPi as anti-tumor agents. We have found that suppression of PARP activity exerts an anti-stemness effect and has a dual impact on autophagy, inducing its activation in the first 24 h (together with down-regulation of the pro-survival mTOR pathway) and preventing autophagosomes fusion to lysosomes at later time-points, in primary glioma cells. In parallel, PARPi triggered the synthesis of lipid droplets (LDs) through ACC-dependent activation of de novo fatty acids (FA) synthesis. Notably, inhibiting ß-oxidation and blocking FA utilization, increased PARPi-induced glioma cell death while treatment with oleic acid (OA) prevented the anti-glioma effect of PARPi. Moreover, LDs fuel glioma cells by inducing pro-survival lipid consumption as confirmed by quantitation of oxygen consumption rates using Seahorse respirometry in presence or absence of OA. In summary, we uncover a novel mechanism by which glioblastoma escapes to anti-tumor agents through metabolic reprogramming, inducing the synthesis and utilization of LDs as a pro-survival strategy in response to PARP inhibition.

Poly(ADP-ribose)polymerase-1 (PARP-1) in carcinogenesis: potential role of PARP inhibitors in cancer treatment.

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear, zinc-finger, deoxyribonucleic acid (DNA)-binding protein that detects specifically DNA strand breaks generated by different genotoxic agents. Whereas activation of PARP-1 by mild genotoxic stimuli facilitates DNA repair and cell survival, severe DNA damage triggers different pathways of cell death, including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. Pharmacological inhibition or genetic ablation of PARP-1 results in a clear benefit in cancer treatment by different mechanisms, including selective killing of homologous recombinationdeficient tumor cells, downregulation of tumor-related gene expression, and decrease in the apoptotic threshold in the cotreatment with chemo- and radiotherapy. We summarize in this review the findings and concepts for the role of PARP-1 and poly(ADP-ribosylation) in the regulation of carcinogenesis and some of the preclinical and clinical data available for these agents, together with the challenges facing the clinical development of these agents.

Modulation of transcription by PARP-1: consequences in carcinogenesis and inflammation.

Post-translational modification of proteins by poly(ADP-ribosyl)ation is involved in the regulation of a number of biological functions. While an 18 member superfamily of poly(ADP-ribose) polymerases (PARP)s has been described PARP-1 accounts for more than 90% of the poly(ADP-ribosyl)ating capacity of the cells. PARP-1 act as a DNA nick sensor and is activated by DNA breaks to cleave NAD(+) into nicotinamide and ADP-ribose to synthesize long branching poly(ADP-ribose) polymers (PAR) covalently attached to nuclear acceptor proteins. Whereas activation of PARP-1 by mild genotoxic stimuli facilitate DNA repair and cell survival, severe DNA damage triggers different pathways of cell death including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. PAR and PARP-1 have also been described as having a function in transcriptional regulation through their ability to modify chromatin-associated proteins and as a cofactor of different transcription factors, most notably NF-kappaB and AP-1. Pharmacological inhibition or genetic ablation of PARP-1 not only provided remarkable protection from tissue injury in various oxidative stress-related disease models but it result in a clear benefit in the treatment of cancer by different mechanisms including selective killing of homologous recombination-deficient tumor cells, down regulation of tumor-related gene expression and decrease in the apoptotic threshold in the co-treatment with chemo and radiotherapy. We will summarize in this review the current findings and concepts for the role of PARP-1 and poly(ADP-ribosyl)ation in the regulation of transcription, oxidative stress and carcinogenesis.

Poly(ADP-ribose) polymerase expression in kidney transplantation: from alfa (alpha) to Omega (Omega).

INTRODUCTION: Overactivation of the enzyme poly(ADP-ribose) polymerase (PARP-1) can be induced by ischemia-reperfusion and involved in the renal injury subsequent to kidney transplant. The poly(ADP-ribosy)lation mechanism alters free radical-induced DNA damage, which is repair by PARP-1 polymer. However, PARP-1 overexpression induces cellular necrosis. Our aim was to study the immunohistochemical PARP-1 expression in kidney transplant biopsies associated with various events. MATERIALS AND METHODS: We studied the nuclear expression of PARP-1 in kidney tubule cells by immunohistochemistry using the monoclonal antibody PAR01 in donor biopsies without acute tubular necrosis (ATN) (n = 60; controls), allografts that suffer ATN (n = 90) or an episode of acute humoral rejection (n = 12) or acute tubulointerstitial rejection (n = 25), or chronic allograft nephropathy (n = 25). Furthermore, we also studied protocol biopsies with subclinical rejection (n = 60). Renal lesions in transplant biopsies were graded blindly using 1997 Banff criteria without any clinical information. RESULTS: Biopsies without morphological features of ATN, namely acute tubulointerstitial rejection, borderline or subclinical rejection, showed lesser PARP-1 expression compared with biopsies with ATN or with ischemic mechanism of acute humoral rejection or chronic allograft nephropathys. We observed an inverse relation between PARP-1 expression and renal function (P < .001). Overall, renal biopsies showing ATN revealed greater expression of PARP-1 (r = 0.785, Pearson test). A significant relationship with PARP-1 expression was demonstrated with renal function (effective diuresis, serum creatinine levels) and pretransplant cold ischemia time (P < .001). CONCLUSION: Kidney transplant events including ischemia were associated with the highest PARP-1 expression and worse allograft renal function.

[Biofeedback therapy for urinary incontinence in children]. / Tratamiento de los trastornos miccionales en niños mediante biofeedback.

INTRODUCTION: We evaluated the efficacy of biofeedback (BFB) therapy in childrens with functional urinary incontinence refractory to conventional treatment. MATERIALS AND METHODS: 34 patients where included (26 girls and 8 boys). They received BFB therapy during the last year for daytime urinary incontinence. 27 patients had urge syndrome with detrusor overactivity, 3 presented giggle incontinence and 4 patients had dysfunctinal voiding. Mean age was 8,4 years. All cases were refractory to bladder training and/or anticholinergics, or recidived after supression. The BFB therapy was carried out with surface electrodes during bladder filling (29 patients) and during voiding (4 patients). One received both therapies. RESULTS: 15 patients (44%) achieved total continence (daytime and nightime) and 7 (20,5%) responded partially. 9 Patients (26%) didn't obtain any benefit and 4 were losed. CONCLUSIONS: In children with functional urinary incontinence pelvic floor muscles training with biofeedback is a simple and effective method. It should be used associated to other therapies, when these fails or repeats after an initial success.

Induction of resistance to endothelin-1's biochemical actions by elevated glucose levels in retinal pericytes.

Because retinal pericytes have contractile properties and are affected by diabetes, we have studied the responsiveness of pericytes to ET-1, a potent vasoconstrictor, in the presence of various concentrations of glucose. Cultured calf retinal pericytes were exposed to glucose levels of 5.5 or 25 mM for up to 8 days. Radioreceptor studies that used [125I]ET-1 showed that pericytes contained high-affinity binding sites with Kd of 3 x 10(-10) M, and these binding affinities were unaffected by glucose concentration. Receptor number appears to be elevated, but this increase was NS. Responsiveness of pericytes to ET-1 was studied with respect to stimulation of DAG and IP3 levels and PKC activities. In contrast to receptor binding, exposure to 25 mM glucose for > 6 days blunted pericyte responsiveness to ET-1. The time course of ET-1 stimulation as measured by [3H]glycerol labeling, and IP3 level showed a 98% increase in [3H]DAG at 10 min and a fourfold increase for IP3, respectively. Cells exposed to 25 mM glucose only had a 32% increase for DAG, and no increase for IP3 was observed. Dose-response studies on the stimulation of [3H]DAG increase showed the range of ET-1's effect to be between 10(-9) and 10(-7) M. At maximum, cells exposed to 5.5 mM glucose had a 70% increase versus only a 30% increase in those exposed to 25 mM glucose. Similarly, ET-1 only increased the total DAG levels in pericytes exposed to 5.5 mM glucose by 41%. PKC activity also was measured because DAG is one of its cellular activators.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of poly (ADP-ribose) polymerase in kidney transplant and its relationship with delayed renal function: multivariate analysis.

UNLABELLED: Kidney allografts undergo pretransplant cold ischemia and consequent ischemia-reperfusion injury (IR). Poly (ADP-Ribose) polymerase (PARP-1) overactivation leads to massive NAD+ consumption and ATP depletion with induction of cellular necrosis under ischemic conditions, which may lead to an increase in acute tubular necrosis (ATN) and a delay in total recovery of renal function (RFR) of the transplanted organ. MATERIALS AND METHODS: Nuclear PARP-1 immunohistochemical expression (clone: PARP01) was studied in 155 paraffin-embedded renal biopsies from suboptimal donors and 95 kidney allograft biopsies with histopathological diagnosis of ATN. RESULTS: In 50% of ATN biopsies, more than 50% of tubular nuclei were immunostained for PARP-1. PARP-1 expression was higher in ATN biopsies than in those from suboptimal donors (2.40 +/- 0.74 vs 0.92 +/- 1.13, P = 0.0001 Mann-Whitney). PARP-1 showed a statistically significant relationship with the time required to achieve effective diuresis (Rho:0.779), with serum creatinine, and with duration of cold ischemia (Rho:0.803). These relationships were stronger in the biopsies with ATN. In conclusion, multivariate analysis demonstrated that PARP-1 expression and cold ischemia duration in kidney biopsies with ATN predicted the short-term delay in total recovery of renal function and serum creatinine in the first month.

Role of poly-(ADP-ribose) polymerase in transplant acute tubular necrosis and its relationship with delayed renal function.

The enzyme poly(ADP-ribose) polymerase (PARP-1) participates in the repair of DNA damaged by genotoxic agents such as oxygen-derived free radicals. If the allograft suffers pretransplant cold ischemia and subsequent ischemia-reperfusion injury (IR), overactivation of PARP-1 can be induced, which may lead to an increase in acute tubular necrosis (ATN) and a delay in total recovery of renal function (RRF) of the transplanted organ. We studied the nuclear expression of PARP-1 in tubular cells by immunohistochemistry with the monoclonal antibody PAR01 in 104 kidney transplant biopsies from allografts with ATN. In 50% of biopsies with ATN, >50% of tubular nuclei were PARP-1+; only 9.6% of biopsies were negative. The increase in the immunohistochemical expression of PARP-1 showed a statistically significant relationship with the duration of cold ischemia, with serum creatinine levels, and with the time required to achieve effective diuresis (P < .0001, Spearman test). Cold ischemia of >24 hours and serum creatinine levels >1.7 mg/dL showed a statistically significant relationship with the highest PARP-1 expression levels (2.83 +/- 0.4 vs 1.36 +/- 0.8, P < .0001, Mann-Whitney U test). We conclude that PARP-1 plays an important role in ATN and RRF and is related to the extent and severity of ATN and to the renal allograft function.

Activation-induced apoptosis in Jurkat cells through a myc-independent mechanism.

Apoptosis can be induced in the human leukemic T-cell line Jurkat when these cells are stimulated by several known T-cell activators. Among the stimuli that activate Jurkat cells, calcium ionophore A23187, phytohemagglutinin and cross-linked monoclonal antibody anti-CD3 are the best inducers of apoptosis. The activator of protein kinase C phorbol-12,13-dibutyrate causes a rapid but transient stimulation of DNA fragmentation and cell death, and soluble monoclonal antibody anti-CD3 has no effect. Furthermore, apoptosis is delayed when Jurkat cells are stimulated simultaneously with calcium ionophore and phorbol ester. We have analysed the mechanism underlying the induction of apoptosis by these agents and found that down-regulation of c-myc expression by pretreatment with the DNA binding antibiotic mithramycin, an inhibitor of c-myc transcription, does not prevent the activation of the apoptotic process. In the light of these results we can conclude that in these leukemic T-cells, activation of apoptosis may occur by a mechanism independent of c-myc expression.

Interactions between radiotherapy and endocrine therapy in breast cancer.

Whenever radiation therapy is given with curative intent there is the risk of serious damage to normal tissue. This risk increases with the dose of radiation, as does the probability of local tumour control. In the attempt to cure, the doses reach a level that inevitably causes some undesirable adverse effects, ranging from undetectable, or minimal, to unacceptably severe. Over the last few years, a number of reports have suggested that the prediction of normal tissue response after radiotherapy may be achieved by assays on samples withdrawn from the patients prior to treatment, although recent reports have described mixed results. The ability to predict tumour response to anti-hormones in patients with breast cancer has important implications with regard to treatment. Recent discoveries promise to provide individualized treatment options. However, there are no data to support that, used jointly, the combination of radiotherapy and hormone therapy may achieve an enhancement of breast cancer tumour response. Nowadays, development in cancer therapy is increasingly arising out of studies in basic science; its implementation in the hands of clinicians is improving the management of patients with cancer. In addition, as the biological aspects of irradiation and hormonal therapy offer an explanation, at least in part, for the outcome observed in patients with breast cancer after therapy, we have focused this review on trying to analyse the most relevant experimental research about the relative roles of radiotherapy and hormonal therapy, the corresponding side-effects and, taking into account recent advances, future areas of research that we consider of major importance in the field.

Correlation of morphological findings with functional reserve in the aging donor: role of the poly (ADP-ribose) polymerase.

INTRODUCTION: The enzyme poly (ADP-ribose) polymerase (PARP-1) participates in the first events of DNA repair in higher organisms. Under conditions of tissue ischemia, this action can lead to significant decreases in NAD(+), massive adenosine triphosphate (ATP) depletion, and cell death. In renal grafts with pretransplantation cold ischemia and subsequent ischemia-reperfusion injury, overactivation of PARP-1 may lead to a higher index of acute tubular necrosis, a delay in total recovery of the function of the transplanted organ, and an early progression to chronic graft nephropathy. The present study examined whether increased tubular expression of PARP-1 in kidneys from aged donors contributed to recipient renal function. MATERIAL AND METHOD: We studied the nuclear expression of PARP-1 using immunohistochemistry with monoclonal antibody PAR01 in 75 kidney biopsy specimens from 40 aged donors. RESULTS: Immunohistochemical expression of PARP-1 showed a statistically significant relationship with donor age (r =.408, P =.006, Spearman test), with time required to achieve effective diuresis (r =.386, P =.01, Spearman test) and with creatinine levels in the first 3 months. We also highlighted a greater intensity of PARP-1 expression in suboptimal donor kidneys that failed to reduce the serum creatinine levels to <1.7 mg/dL (creatinine <1.7 PARP: 1.29 +/- 1.49 vs creatinine >1.7 PARP: 2.29 +/- 1.33, P =.047, Mann-Whitney U test). CONCLUSION: We conclude that the determination of PARP-1 in biopsy specimens from aged donors may be a useful predictive factor for renal graft function.

Effects of starvation, diabetes and carbon tetrachloride intoxication on rat kidney cortex and liver pyruvate carboxylase levels.

Pyruvate carboxylase (PC) has been quantified in rat liver and kidney cortex under experimental conditions that modify the gluconeogenic response in both organs: fasting, carbon tetrachloride-induced liver degeneration and alloxan-induced diabetes. Enzymatic activity has been assayed by a 14CO2-fixation method. The amount of enzyme has been determined by competitive ELISA using antibodies raised against the purified rat kidney cortex enzyme. Purified fractions of rat-liver and rat-kidney cortex PC have been used as standards. Fasting and carbon tetrachloride administration induced a significant increase (25% to 30%) in the amount of enzyme in liver and kidney cortex. Alloxan-induced diabetes produced a nearly two-fold increase in the hepatic levels of enzyme without a significant modification in the content of the renal enzyme. These results are discussed on the basis of the different metabolic implications of both organs during the physiological or toxic treatments.

Interaction between PARP-1 and HIF-2α in the hypoxic response.

Hypoxia-inducible factors (HIFs) mediate the transcriptional adaptation of hypoxic cells. The extensive transcriptional programm regulated by HIFs involves the induction of genes controlling angiogenesis, cellular metabolism, cell growth, metastasis, apoptosis, extracellular matrix remodeling and others. HIF is a heterodimer of HIF-α and HIF-ß subunits. In addition to HIF-1α, HIF-2α has evolved as an isoform that contributes differently to the hypoxic adaptation by performing non-redundant functions. Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear protein involved in the control of DNA repair and gene transcription by modulating chromatin structure and acting as part of gene-specific enhancer/promoter-binding complexes. Previous results have shown that PARP-1 regulates HIF-1 activity. In this study, we focused on the cross-talk between HIF-2α and PARP-1. By using different approaches to suppress PARP-1, we show that HIF-2α mRNA expression, protein levels and HIF-2-dependent gene expression, such as ANGPTL4 and erythropoietin (EPO), are regulated by PARP-1. This regulation occurs at both the transcriptional and post-trancriptional level. We also show a complex formation between HIF-2α with PARP-1. This complex is sensitive to PARP inhibition and seems to protect against the von Hippel-Lindau-dependent HIF-2α degradation. Finally, we show that parp-1(-/-) mice display a significant reduction in the circulating hypoxia-induced EPO levels, number of red cells and hemoglobin concentration. Altogether, these results reveal a complex functional interaction between PARP-1 and the HIF system and suggest that PARP-1 is involved in the fine tuning of the HIF-mediated hypoxic response in vivo.

Poly(ADP-ribose)-dependent regulation of Snail1 protein stability.

Snail1 is a master regulator of the epithelial-mesenchymal transition (EMT) and has been implicated in key tumor biological processes such as invasion and metastasis. It has been previously shown that poly(ADP-ribose) polymerase-1 (PARP-1) knockdown, but not PARP inhibition, downregulates the expression of Snail1. In this study we have characterized a novel regulatory mechanism controlling Snail1 protein expression through poly(ADP-ribosyl)ation. The effect is not only limited to repression of Snail1 transcription but also to downregulated Snail1 protein stability. PARP-1 (but not PARP-2) poly(ADP) ribosylates Snail1, both in vivo and in vitro, and interacts with Snail1, an association that is sensitive to PARP inhibitors. PARP inhibition has also clear effects on EMT phenotype of different tumor cells, including Snail1 downregulation, E-cadherin upregulation, decreased cell elongation and invasiveness. Therefore, this study reveals a new regulatory mechanism of Snail1 activation through poly(ADP-ribosyl)ation with consequences in malignant transformation through EMT.

Inhibition of poly (ADP-ribose) polymerase-1 enhances doxorubicin activity against liver cancer cells.

The purpose of this study was to investigate whether PARP-1 inhibition sensitizes human liver cancer cell lines to doxorubicin treatment. Both the addition of PARP-1 inhibitor (ANI) and depletion by means of stable siRNA significantly enhanced the growth inhibition induced by the DNA damage agents used. This effect was associated with an accumulation of unrepaired DNA, with a reduction in EGFR and Bcl-xL gene expression as well as with positive annexin-V staining. These results provide novel evidence of the direct role of PARP-1 in tumour chemoresistance in relation to its effects on the transcription of key genes involved in tumour survival.

Human umbilical cord stromal stem cell express CD10 and exert contractile properties.

BACKGROUND: It has been demonstrated that human umbilical cord stromal stem cells (UCSSCs) are bio-equivalent to bone marrow mesenchymal stem cells. However, little is known about their tissue origin or in vivo functions, and data on their expansion properties are limited due to early senescence in the culture methods described to date. METHODS: UC sections and cultured UCSSCs were analyzed with a panel of 12 antibodies. UCSSCs were grown in low-FCS containing medium at 5% or 21% oxygen and were assayed for their clonogenic properties, karyotype stability, expression of specific cellular markers, and multi-lineage potential. UCSSC contractile properties were evaluated by using collagen gel contraction assays under cytokine stimulus. RESULTS: Immunohistochemistry studies showed that the UCSSCs were derived from the Wharton's jelly and not from the vascular smooth muscle sheath of the blood vessels. UCSSC growth properties were increased in a 5% oxygen atmosphere in comparison to normoxic culture conditions. In both culture conditions, UCSSCs were CD14-, CD34-, and CD45-negative while expressing high levels of CD73, CD90 and CD105 and maintaining their differentiation potentialities. UCSSCs expressed alpha smooth muscle actin and behaved as functional myofibroblasts when cellular contraction was challenged with appropriate stimuli. CONCLUSIONS: UCSCs are mesenchymal stem cells that reside in the perivascular area of Wharton's jelly and are phenotypically and functionally related to myofibroblasts.

Apoptosis of haematopoietic cells upon thymidylate synthase inhibition is independent of p53 accumulation and CD95-CD95 ligand interaction.

Treatment of haematopoietic BA/F3 cells with the thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine (FUdR) activated apoptosis through a mechanism that required continuous protein synthesis and was inhibited by Bcl-2 over-expression. Analysis of p53 levels in cells treated with FUdR indicated a marked accumulation of this protein. Accumulation of p53 was also observed in cells over-expressing Bcl-2. In BA/F3 cells transfected with a cDNA coding for the human papilloma virus protein E6, p53 accumulation after FUdR treatment was inhibited markedly. However, apoptosis was induced in both control and E6 cells to a similar extent. The role of the CD95/CD95 ligand (CD95L) system in FUdR-induced apoptosis was also assessed. As determined by reverse transcriptase PCR, BA/F3 expressed a low constitutive level of CD95L mRNA, which decreased following FUdR treatment. Moreover, blocking CD95-CD95L interactions with antagonistic CD95 monoclonal antibody did not prevent drug-induced apoptosis. Furthermore, analysis of caspase involvement showed important differences in apoptosis induced by CD95-triggering or FUdR treatment. In summary, these results suggest that apoptosis induced by thymineless stress in haematopoietic BA/F3 cells occurs by a mechanism that does not require accumulation of p53 and which is independent of CD95-CD95L interactions.