The pulvinar nucleus and antidepressant treatment: dynamic modeling of antidepressant response and remission with ultra-high field functional MRI

Functional magnetic resonance imaging (fMRI) successfully disentangled neuronal pathophysiology of major depression (MD), but only a few fMRI studies have investigated correlates and predictors of remission. Moreover, most studies have used clinical outcome parameters from two time points, which do not optimally depict differential response times. Therefore, we aimed to detect neuronal correlates of response and remission in an antidepressant treatment study with 7 T fMRI, potentially harnessing advances in detection power and spatial specificity. Moreover, we modeled outcome parameters from multiple study visits during a 12-week antidepressant fMRI study in 26 acute (aMD) patients compared to 36 stable remitted (rMD) patients and 33 healthy control subjects (HC). During an electrical painful stimulation task, significantly higher baseline activity in aMD compared to HC and rMD in the medial thalamic nuclei of the pulvinar was detected (p = 0.004, FWE-corrected), which was reduced by treatment. Moreover, clinical response followed a sigmoid function with a plateau phase in the beginning, a rapid decline and a further plateau at treatment end. By modeling the dynamic speed of response with fMRI-data, perigenual anterior cingulate activity after treatment was significantly associated with antidepressant response (p < 0.001, FWE-corrected). Temporoparietal junction (TPJ) baseline activity significantly predicted non-remission after 2 antidepressant trials (p = 0.005, FWE-corrected). The results underline the importance of the medial thalamus, attention networks in MD and antidepressant treatment. Moreover, by using a sigmoid model, this study provides a novel method to analyze the dynamic nature of response and remission for future trials.

Sustained consumption of cocoa-based dark chocolate enhances seizure-like events in the mouse hippocampus

While the consumption of caffeine and cocoa has been associated with a variety of health benefits to humans, some authors have proposed that excessive caffeine intake may increase the frequency of epileptic seizures in humans and reduce the efficiency of antiepileptic drugs. Little is known, however, about the proconvulsant potential of the sustained, excessive intake of cocoa on hippocampal neural circuits. Using the mouse as an experimental model, we examined the effects of the chronic consumption of food enriched in cocoa-based dark chocolate on motor and mood-related behaviours as well as on the excitability properties of hippocampal neurons. Cocoa food enrichment did not affect body weights or mood-related behaviours but rather promoted general locomotion and improved motor coordination. However, ex vivo electrophysiological analysis revealed a significant enhancement in seizure-like population spike bursting at the neurogenic dentate gyrus, which was paralleled by a significant reduction in the levels of GABA-α1 receptors thus suggesting that an excessive dietary intake of cocoa-enriched food might alter some of the synaptic elements involved in epileptogenesis. These data invite further multidisciplinary research aiming to elucidate the potential deleterious effects of chocolate abuse on behaviour and brain hyperexcitability.

Default mode network deactivation during emotion processing predicts early antidepressant response

Several previous functional magnetic resonance imaging (fMRI) studies have demonstrated the predictive value of brain activity during emotion processing for antidepressant response, with a focus on clinical outcome after 6-8 weeks. However, longitudinal studies emphasize the paramount importance of early symptom improvement for the course of disease in major depressive disorder (MDD). We therefore aimed to assess whether neural activity during the emotion discrimination task (EDT) predicts early antidepressant effects, and how these predictive measures relate to more sustained response. Twenty-three MDD patients were investigated once with ultrahigh-field 7T fMRI and the EDT. Following fMRI, patients received Escitalopram in a flexible dose schema and were assessed with the Hamilton Depression Rating Scale (HAMD) before, and after 2 and 4 weeks of treatment. Deactivation of the precuneus and posterior cingulate cortex (PCC) during the EDT predicted change in HAMD scores after 2 weeks of treatment. Baseline EDT activity was not predictive of HAMD change after 4 weeks of treatment. The precuneus and PCC are integral components of the default mode network (DMN). We show that patients who exhibit stronger DMN suppression during emotion processing are more likely to show antidepressant response after 2 weeks. This is, to our knowledge, the first study to show that DMN activity predicts early antidepressant effects. However, DMN deactivation did not predict response at 4 weeks, suggesting that our finding is representative of early, likely treatment-related, yet unspecific symptom improvement. Regardless, early effects may be harnessed for optimization of treatment regimens and patient care.

Hydrogen bonding and Raman, IR, and 2D-IR spectroscopy of dilute HOD in liquid D2O

We present improvements on our previous approaches for calculating vibrational spectroscopy observables for the OH stretch region of dilute HOD in liquid D2O. These revised approaches are implemented to calculate IR and isotropic Raman spectra, using the SPC/E simulation model, and the results are in good agreement with experiment. We also calculate observables associated with three-pulse IR echoes: the peak shift and 2D-IR spectrum. The agreement with experiment for the former is improved over our previous calculations, but discrepancies between theory and experiment still exist. Using our proposed definition for hydrogen bonding in liquid water, we decompose the distribution of frequencies in the OH stretch region in terms of subensembles of HOD molecules with different local hydrogen-bonding environments. Such a decomposition allows us to make the connection with experiments and calculations on water clusters and more generally to understand the extent of the relationship between transition frequency and local structure in the liquid.

Survey on the Listeria Contamination of Ready-to-Eat Food Products and Household Environments in Vienna, Austria

Qualitative and quantitative contamination of ready-to-eat food-stuffs with the pathogen Listeria monocytogenes was studied in 1586 samples collected from 103 supermarkets (n = 946) and 61 households (n = 640) in Vienna, Austria. Seventeen groups of ready-to-eat foods were classified into three risk categories for contamination (CP1-CP3). Three to four samples were randomly collected at the retail level from each CP. Regarding the households, the sampling procedure was started with food items of CP1, and if not available, was continued with sampling of food items of CP2 and finally of CP3. Additionally, 184 environmental samples (swabs from the kitchen area, dust samples from the vacuum cleaner) and faecal samples (household members and pet animals) were included. One-hundred and twenty-four (13.1%) and 45 (4.8%) samples out of 946 food samples collected from food retailers tested positive for Listeria spp. and L. monocytogenes, respectively, with five smoked fish samples exceeding the tolerated limit of 100 CFU/g food. Food-stuffs associated with the highest risk of contamination were twice as frequently contaminated with L. monocytogenes as food-stuffs associated with a medium risk of contamination. Products showing the highest contamination rate were fish and seafood (19.4%), followed by raw meat sausages (6.3%), soft cheese (5.5%) and cooked meat products/patés (4.5%). The overall contamination rate of foods collected at the household level was more than two times lower. Only 5.6% and 1.7% of 640 food-stuffs analysed tested positive for Listeria spp. and L. monocytogenes, respectively. However, CP1 foods were rarely collected. Pulsed-field gel electrophoresis (PFGE) typing of the collected L. monocytogenes isolates revealed a high degree of diversity between the isolates, with some exceptions. PFGE typing of isolates harvested from green-veined cheese revealed a match among strains, although the manufacturer seemed to be distinguishable. Typing of household strains revealed an epidemiological link within one family. In this case, food-stuffs and the kitchen environment were contaminated by an indistinguishable isolate. In addition, the same isolate was collected from a pooled faecal sample of the household members suggesting that consumption of even low contaminated food items (<100 CFU/g) results in Listeria shedding after the passage through the gut.

LST1: a gene with extensive alternative splicing and immunomodulatory function

The gene of the leukocyte-specific transcript (LST1) is encoded within the TNF region of the human MHC. The LST1 gene is constitutively expressed in leukocytes and dendritic cells, and it is characterized by extensive alternative splicing. We identified 7 different LST1 splice variants in PBMC; thus, 14 LST1 splice variants (LST1/A-LST1/N) have been detected in various cell types. These isoforms code for transmembrane as well as soluble LST1 proteins characterized by two alternative open reading frames at their 3' end. We demonstrate the presence of the transmembrane variant LST1/C on the cell surface of the monocytic cell lines U937 and THP1. Recombinant expression of LST1/C permitted its profound inhibitory effect on lymphocyte proliferation to be observed. In contrast, the alternative transmembrane variant LST1/A, the extracellular domain of which shows no amino acid sequence homology to LST1/C exerted a weaker but similar inhibitory effect on PBMC. These data demonstrate the protein expression of LST1 on the cell surface of mononuclear cells, and they show an inhibitory effect on lymphocyte proliferation of two LST1 proteins although they have only a very short amino acid homology.

pADPRT-2: a novel mammalian polymerizing(ADP-ribosyl)transferase gene related to truncated pADPRT homologues in plants and Caenorhabditis elegans

Until recently, poly(ADP-ribosyl)ation was supposed to be confined only to polymerizing(ADP-ribosyl)transferase/(ADP-ribose)polymerase (E.C. 2.4.2.30). Here, we present novel polymerizing(ADP-ribosyl)transferase homologues from mouse and man that lack all of the N-terminal DNA binding and BRCA1 C-terminus domains and will be designated polymerizing(ADP-ribosyl)transferase-2 as distinguished from the classical polymerizing(ADP-ribosyl)transferase (polymerizing(ADP-ribosyl)transferase-1). The murine polymerizing(ADP-ribosyl)transferase-2 gene shares three identical intron positions with its Caenorhabditis elegans (EMBL nucleotide sequence database Z47075) and one with the Arabidopsis thaliana homologue ('APP', GenBank database AF069298). Expression of the murine polymerizing(ADP-ribosyl)transferase-2 gene was elevated in spleen, thymus and testis and the corresponding poly(ADP-ribosyl)ation activity might account for most of the residual poly(ADP-ribosyl)ation observed in polymerizing(ADP-ribosyl)transferase-1(-/-) mice.

Poly ADP-ribosylation: a DNA break signal mechanism

Recent evidence obtained with transgenic knockout mice suggests that the enzyme poly(ADP-ribose)polymerase (PARP) does not play a direct role in DNA break processing. Nevertheless, inactivation of the catalytic or the DNA nick-binding functions of PARP affects cellular responses to genotoxins at the level of cell survival, sister chromatid exchanges and apoptosis. In the present report, we conceptualize the idea that PARP is part of a DNA break signal mechanism. In vitro screening studies revealed the existence of a protein family containing a polymer-binding motif of about 22 amino acids. This motif is present in p53 protein as well as in MARCKS, a protein involved in the regulation of the actin cytoskeleton. Biochemical analyses showed that these sequences are directly targeted by PARP-associated polymers in vitro, and this alters several molecular functions of p53- and MARCKS protein. PARP-deficient knockout mice from transgenic mice were found to exhibit several phenotypic features compatible with altered DNA damage signaling, such as downregulation and lack of responsiveness of p53 protein to genotoxins, and morphological changes compatible with MARCKS-related cytoskeletal dysfunction. The knockout phenotype could be rescued by stable expression of the PARP gene. We propose that PARP-associated polymers may recruit signal proteins to sites of DNA breakage and reprogram their functions.

Bcl-2 interferes with the execution phase, but not upstream events, in glucocorticoid-induced leukemia apoptosis

Due to their growth arrest- and apoptosis-inducing ability, glucocorticoids (GC) are widely used in the therapy of various lymphoid malignancies. Cell death is associated with activation of members of the interleukin-1beta-converting enzyme (ICE) protease/caspase family and, is presumably prevented by the anti-apoptotic protein Bcl-2. To further address the role of Bcl-2 in GC-mediated cytotoxicity, we generated subclones of the GC-sensitive human T-cell acute lymphoblastic leukemia line CCRF-CEM, in which transgenic Bcl-2 expression is regulated by tetracycline. Up to about 48 h, exogenous Bcl-2 almost completely protected these cells from apoptosis, digestion of poly-ADP ribose polymerase (PARP) and generation of Asp-Glu-Val-Asp cleaving (DEVDase) activity. However, when the cells were cultured for another 24 h in the continuous presence of GC, they underwent massive apoptosis that was associated with DEVDase activity and PARP cleavage. Bcl-2 did not markedly affect GC-mediated growth arrest, thereby separating the anti-proliferative from the apoptosis-inducing effect of GC. Moreover, Bcl-2 did not prevent the dramatic reduction in the levels of several mRNAs observed during GC treatment, including the transgenic Bcl-2 mRNA. Thus, Bcl-2 can be placed upstream of effector caspase activation, but downstream of other GC-regulated events, such as growth arrest and the potentially critical repression of steady state levels of multiple mRNA.

Analysis of the TPA regulatory element in the genomic poly(ADP-ribose) synthetase gene in human leukemia U937 cells

The human leukemia U937 cells differentiate into monocyte/macrophage-like cells when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA). We observed that during this process, both protein and mRNA levels for PARS markedly decreased in U937 cells. Through deletion analysis of the PARS regulatory gene, we found that the sequence within the first intron region was responsible for the TPA-dependent repression. Electrophoretic mobility shift assays (EMSAs) and Southwestern blot analysis indicate that this element bound specifically to a nuclear protein. TPA treatment abolished the binding of the protein in U937 cells but not in HeLa cells. DNase I footprinting data show that the cis regulatory element is located between residues 328 and 383. We further examined the function of this cis element (BS207) in a basal promoter regulatory reporter construct and found that this cis element (BS207) functions as an enhancer via the binding of an unknown trans-acting factor. TPA treatment diminished the binding activity of the factor in U937 cells, resulting in a decrease in the enhanced activity to the basal level. These results suggest that abolishment of the binding of a special nuclear protein to the first intron of the PARS gene is related to the TPA-responsive downregulation of PARS in U937 cells.

Escherichia coli bacteriophage T1 DNA methyltransferase appears to interact with Escherichia coli enolase

Infection of Escherichia coli cells with bacteriophage T1 induces synthesis of a bacteriophage-specific DNA methyltransferase (M.EcoT1, EC No: 2.1.1.72) with a specificity for adenine residues in the sequence 5'-GATC-3'. Purification of M.EcoT1 allowed the determination of the coding sequence of the gene (Schneider-Scherzer et al., 1990). The peptide of the entire coding sequence was over-expressed as a histidine-hexapeptide tagged protein in E. coli. Affinity purification using a Ni2+ chelating (Ni-NTA) resin yielded a recombinant enzyme with almost the same enzymatic properties as the protein purified from T1 infected E. coli cells. Interestingly, in both purification procedures, a protein with a molecular weight of 50000 was found to copurify with M.EcoT1. The N-terminal amino acid sequence identified these proteins in both cases as E. coli enolase (EC No: 4.2.1.11).

p53-induced apoptosis in the human T-ALL cell line CCRF-CEM

The tumor suppressor p53 has been implicated in apoptosis induction and is mutated in human T-ALL CCRF-CEM cells. To investigate possible consequences of wild-type p53 loss, we reconstituted CEM-C7H2, a subclone of CCRF-CEM, with a temperature-sensitive p53 allele (p53ts). Stably transfected lines expressed high levels of p53ts and shift to the permissive temperature (32 degrees C) caused rapid induction of p53-regulated genes, such as p21(CIP1/WAF1), mdm-2 and bax. This was followed by extensive apoptosis within 24 h to 36 h, supporting the notion that mutational p53 inactivation contributed to the malignant phenotype. p53-dependent apoptosis was preceded by digestion of poly(ADP-ribose) polymerase, a typical target of interleukin-1beta-converting enzyme (ICE)-like proteases/caspases, and was markedly resistant to the ICE/caspase-1 and FLICE/caspase-8 inhibitor acetyl-Tyr-Val-Ala-Asp.chloromethylketone (YVAD), but sensitive to the CPP32/caspase-3 inhibitor benzyloxycarbonyl-Asp-Glu-Val-Asp.fluoromethylketone (DEVD) and benzyloxycarbonyl-Val-Ala-Asp.fluoromethylketone (zVAD), a caspase inhibitor with broader specificity. This indicated an essential involvement of caspases, but argued against a significant role of ICE/caspase-1 or FLICE/caspase-8. Actinomycin D or cycloheximide prevented cell death, suggesting that, in this system, p53-induced apoptosis depends upon macromolecule biosynthesis. Introduction of functional p53 into CEM cells enhanced their sensitivity to the DNA-damaging agent doxorubicin, but not to the tubulin-active compound vincristine. Thus, mutational p53 inactivation in ALL might entail relative resistance to DNA-damaging, but not to tubulin-destabilizing, chemotherapy.

The interleukin 1beta-converting enzyme inhibitor CrmA prevents Apo1/Fas- but not glucocorticoid-induced poly(ADP-ribose) polymerase cleavage and apoptosis in lymphoblastic leukemia cells

Glucocorticoids (GC) induce programmed cell death (apoptosis) in immature lymphocytes and are an essential component in the therapy of acute lymphatic leukemia. The mechanism underlying GC-induced apoptosis particularly in leukemia cells is, however, not well understood. Most forms of apoptosis seem to employ a common final effector pathway characterized by specific proteolytic events mediated by interleukin 1beta-converting enzyme (ICE) and/or other ICE-like cysteine proteases. These events may result in the morphologic changes characteristic of apoptosis. To determine whether a similar proteolytic pathway is activated during GC-induced leukemia cell apoptosis, we investigated poly(ADP-ribose) polymerase (PARP), a typical target of ICE-like proteases, during GC-induced apoptosis of the human acute T-cell leukemic cell line CEM-C7H2. Our studies showed proteolytic PARP cleavage suggestive of activation of ICE-like proteases that preceeded morphologic signs of apoptosis. We further established stably transfected CEM-C7H2 sublines expressing the cowpox virus protein CrmA that inhibits some, but not all, ICE-like proteases. GC-induced PARP cleavage and apoptosis were neither inhibited nor delayed in crmA-expressing cell lines. In contrast, crmA expression rendered the same lines resistant to Apo1/Fas-induced PARP cleavage and apoptosis. Thus, different proteases might be activated during the effector phases of GC-and Apo1/Fas-induced apoptosis in human leukemia cells.

Modulation of Apo-1/Fas (CD95)-induced programmed cell death in myeloma cells by interferon-alpha 2

The Apo-1/Fas (CD95) antigen is known to be involved in the process of T cell-mediated target cell killing and has recently been shown to be expressed on myeloma cell lines and native malignant plasma cells. Several cytokines have been reported to interfere with spontaneous and even Apo-1/Fas-induced apoptosis, but no attempt has been made yet to investigate these interactions and the possible underlying mechanisms in myeloma cells. Since in myeloma patients Interferon (IFN)-alpha2 displays a profound therapeutic effect in vivo, which is usually attributed to its growth inhibitory and/or immunomodulatory capacity, we set out to study the potential interference of IFN-alpha2 with Apo-1/Fas-induced apoptosis. Contrary to expectations, IFN-alpha2 reduced the degree of apoptosis caused by the treatment of five Apo-1/Fas-sensitive myeloma cell lines with a Fas monoclonal antibody (mAb). Simultaneous application of IFN-alpha2 and Fas mAb was superior to the prolonged (i.e. >8 h) preincubation with the cytokine as far as inhibition of Apo-1/Fas-induced apoptosis was concerned. This effect of IFN-alpha2 was neither explained by a down-regulation of the Apo-1/Fas receptor nor caused by modulation of the expression levels of c-myc, bcl-2-, bcl-xL, bax- or p53 genes. IFN-alpha2 did not alter the Apo-1/Fas-induced activity of Mitogen-activated protein kinase (MAPK) 1 and did not inhibit the Apo-1/Fas-mediated proteolytic cleavage of ADP-ribosyltransferase, a substrate of Interleukin-beta1 converting enzyme (ICE) and homologues. However, activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) mimicked the effects of IFN-alpha2. Furthermore, the bis-indolylmaleimide GF 109203X, a specific inhibitor of PKC, inhibited the effect of PMA as well as that of IFN-alpha2 on Apo-1/Fas-induced apoptosis. These results point to a PKC-dependent mechanism of transient interaction between the intracellular signaling along the IFN-alpha2 and the Apo-1/Fas pathway (downstream of MAPK signaling as well as of ICE homologues), which becomes exhausted by prolonged stimulation with the cytokine. According to our data IFN-alpha2, applied continuously and in high doses resembling the therapeutic situation in vivo, inhibits myeloma growth. However, based on the observed inhibitory effect of IFN-alpha2 on Apo-1/Fas-induced apoptosis, a partial inhibition of the natural immune surveillance on myeloma cells by endogenous IFN-alpha2 present in the bone marrow microenvironment of this malignancy should be investigated.

Characterization of detergent-solubilized beef liver mitochondrial NAD+ glycohydrolase and its truncated hydrosoluble form

Membrane-bound beef liver mitochondrial NAD+ glycohydrolase (NADase) was partially purified after its solubilization by either detergent or crude pancreatic lipase, steapsin. Solubilization by steapsin yielded a homogeneous water-soluble enzyme. A fluorescence assay was developed that allowed visualization of NADase activity directly within the gel after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent molecular masses of the detergent- and steapsin-solubilized forms were estimated to be about 30,000 and 28,000, respectively. The small part that was cleaved by steapsin represents presumably the membrane anchor of the mitochondrial NADase, as its removal converted the enzyme from a highly hydrophobic to a hydrosoluble protein. The fluorescence staining for activity was also successfully applied to other NADases. Kinetic analyses of the two forms of solubilized mitochondrial NADase revealed that the catalytic properties were unaffected after the steapsin treatment. Neither the binding affinity of the substrate analog 1, N6-etheno-NAD+ nor the inhibition by nicotinamide differed significantly between these two forms of the enzyme. Moreover, the dependence of the enzyme activity on temperature, pH, or ionic strength was also similar for both preparations. However, activity of the detergent-solubilized but not of the truncated steapsin-solubilized enzyme was strongly dependent on the presence of bivalent metal ions such as ZN2+. These results suggest that the membrane part of the mitochondrial NAD+ glycohydrolase is not required for catalysis. It appears, however, to be of importance for the regulation of the enzyme.

Induction of endothelial cell differentiation into capillary-like structures by substance P

Angiogenesis is an important process in inflammatory diseases and wound healing. We observed that the proinflammatory neuropeptide, substance P, stimulated angiogenesis in an in vitro model using human umbilical cord vein endothelial cells cultured on a basement membrane (Matrigel) substrate. Substance P stimulated endothelial cell differentiation into capillary-like structures in a dose-dependent manner. Stimulation of endothelial cell differentiation is a newly recognized biological function of substance P. The increased levels of substance P found in chronic inflammatory conditions may play an important role in tissue repair by promoting the development of new vessels and thus achieving compensation for ischemia.

Prenatal effects of betamethasone-L-carnitine combinations on fetal rat lung

Lungs of fetal rats between the 18th and 20th gestational day (total gestation lasting 22 days) were examined. There was a significant increase (p < 0.01) of the dipalmitoyl phosphatidylcholine content from day 19 to day 20 of gestation. In the second trial, pregnant rats were treated with different doses of betamethasone, L-carnitine, betamethasone-L-carnitine combinations, and saline (controls) for three days before Cesarean section on the 19th gestational day. Maternal injections of 0.10 mg/kg body weight betamethasone and 100 mg/kg body weight L-carnitine significantly (p < 0.05, p < 0.01 respectively) increased the dipalmitoyl phosphatidylcholine content of fetal lungs. Combinations of either 0.05 or 0.10 mg/kg body weight betamethasone with 100 mg L-carnitine also significantly increased the dipalmitoyl phosphatidylcholine content of the fetal lungs above control values (p < 0.001) and values achieved with betamethasone alone (p < 0.05). Maternal treatment with a betamethasone-L-carnitine combination on day 19 of gestation resulted in dipalmitoyl phosphatidylcholine levels comparable to those found on the 20th gestational day during normal lung maturation. Fetal rats delivered on the 20th gestational day survived, while fetuses delivered on the 19th gestational day did not survive.

Identification and purification of a bovine liver mitochondrial NAD(+)-glycohydrolase

Nonenzymatic ADP-ribosylation of mitochondrial proteins is thought to play a role in the regulation of Ca2+ efflux from mitochondria. It has been shown that intramitochondrial ADP-ribose is generated by a specific NAD(+)glycohydrolase, which catalizes hydrolysis of NAD+ to ADP-ribose and nicotinamide. We purified this enzyme from bovine liver mitochondrial membranes. The final preparation had a 1660-fold purified enzyme activity and contained a main protein band with an apparent molar mass of 32,000 in a SDS-polyacrylamide gel. The identity of this protein band with NAD(+)-glycohydrolase was verified by renaturation of its enzymatic activity. Partial amino acid sequence information was obtained from two enzyme fragments after proteolytic cleavage of the protein band in the SDS-polyacrylamide gel. Searches in protein databases revealed that an arginine ADP-ribosyl hydrolase harbours two stretches of amino acids that are highly similar to the partial NAD(+)-glycohydrolase sequences.

Specific neurotrophin binding to leucine-rich motif peptides of TrkA and TrkB

The extracellular domains of the TrkA and TrkB neurotrophin receptors contain defined structural modules such as immunoglobulin-like domains and leucine-rich motifs (LRMs) [Schneider and Schweiger, Oncogene 6 (1991) 1807-1811]. Recently, the second LRM of TrkA was identified as a functional nerve growth factor (NGF) binding site [Windisch et al, J. Biol. chem. (1995) in press]. A peptide corresponding to this region effectively bound NGF and blocked binding of NGF to the recombinant extracellular domain of TrkA. The corresponding TrkB peptide exhibited the same effects with respect to brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4), indicating that all three TrkB ligands utilize this same binding site. Isolated LRMs therefore embody independent functional entities.

Brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4 bind to a single leucine-rich motif of TrkB

TrkB is a member of the Trk family of neurotrophin receptors. Its extracellular domain exhibits the same modular structure found in its homologs, TrkA and TrkC, consisting of an N-terminal LRM3 cassette and two immunoglobulin-like modules (Ig2 domain) adjacent to the membrane. The LRM3 cassette comprises two cysteine-rich clusters framing a tandem array of three leucine-rich motifs (LRMs). On the basis of the recent identification of a nerve growth factor (NGF) binding site within TrkA, the ability of the different structural entities within the extracellular domain of TrkB to bind the various neurotrophins was determined by using a recombinant receptor approach. Brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) bound to the LRM3 cassette of TrkB, whereas NGF did not. These binding characteristics evidently reflect in vivo specificities. A more precise mapping of the region(s) responsible for binding BDNF, NT-3, and NT-4 identified the second leucine-rich motif of TrkB as a functional unit capable of binding all three neurotrophins. The affinities and kinetics that this short stretch of amino acids exhibited with respect to the different neurotrophins were clearly akin to those observed for cells ectopically expressing TrkB receptors. With 24 amino acids determining the affinities and kinetics of the interactions with three different partners, the leucine-rich motif is strongly established as one of the most potent and flexible protein--protein interaction motifs.

Mice lacking ADPRT and poly(ADP-ribosyl)ation develop normally but are susceptible to skin disease

Poly(ADP-ribosyl)ation is catalyzed by NAD+: protein(ADP-ribosyl) transferase (ADPRT), a chromatin-associated enzyme which, in the presence of DNA breaks, transfers ADP-ribose from NAD+ to nuclear proteins. This post-translational modification has been implicated in many fundamental processes, like DNA repair, chromatin stability, cell proliferation, and cell death. To elucidate the biological function of ADPRT and poly(ADP-ribosyl)ation in vivo the gene was inactivated in the mouse germ line. Mice homozygous for the ADPRT mutation are healthy and fertile. Analysis of mutant tissues and fibroblasts isolated from mutant fetuses revealed the absence of ADPRT enzymatic activity and poly(ADP-ribose), implying that no poly(ADP-ribosyl)ated proteins are present. Mutant embryonic fibroblasts were able to efficiently repair DNA damaged by UV and alkylating agents. However, proliferation of mutant primary fibroblasts as well as thymocytes following gamma-radiation in vivo was impaired. Moreover, mutant mice are susceptible to the spontaneous development of skin disease as approximately 30% of older mice develop epidermal hyperplasia. The generation of viable ADPRT-/-mice negates an essential role for this enzyme in normal chromatin function, but the impaired proliferation and the onset of skin lesions in older mice suggest a function for ADPRT in response to environmental stress.

Pregnancy-related changes of carnitine and acylcarnitine concentrations of plasma and erythrocytes

Total-, free-, and acylcarnitine concentrations were determined in whole blood, plasma, and red blood cells of 88 women during pregnancy. Already in the 12th week of gestation the mean whole blood carnitine level was significantly (p < 0.01) lower than those of the controls. From the 12th gestational week up to parturition there was a further significant (p < 0.01) decrease. This reduction of total carnitine in whole bloods was mainly caused by a significant (p < 0.01) decrease of free carnitine levels, since no marked changes of short chain acylcarnitine values were found throughout pregnancy. The contribution of red blood cell L-carnitine to whole blood carnitine increased significantly (p < 0.05) to 61% at delivery versus 39% (controls). In umbilical cord blood free and total carnitine levels were significantly (p < 0.05) higher than the corresponding maternal levels. The contribution of red blood cell L-carnitine to whole blood carnitine was higher in cord blood than in maternal blood. The results of the present study demonstrate that during pregnancy whole blood and plasma carnitine levels decrease to those levels found in patients with carnitine deficiency. Also the percentage of acylcarnitine on total carnitine, found in the present study, is characteristic for a secondary carnitine deficiency. Thus L-carnitine substitution in pregnant women, especially in risk pregnancies, may be advantageous.

On the biological role of the nuclear polymerizing NAD+: protein(ADP-ribosyl) transferase (ADPRT): ADPRT from Dictyostelium discoideum and inactivation of the ADPRT gene in the mouse

Two approaches have been used to elucidate the role of the nuclear polymerizing NAD+:protein(ADP-ribosyl)-transferase (ADPRT): i) comparison of the primary structure of Dictyostelium discoideum ADPRT derived from a 2 kb, partial cDNA sequence with the mammalian, fish, amphibian and insect counterparts revealed an overall homology of 25%. Whereas the automodification domain was not conserved at all, the NAD+ binding domain (aa 859-908) showed more than 70% identical amino acids in all species. Together with the similar enzymatic properties of the ADPRTs the genetic conservation underlined the notion that ADPRT plays a major role in various cellular processes; and ii) inactivation of the ADPRT gene in murine embryonic stem cells by homologous recombination led to mouse strains with a complete lack of nuclear poly(ADP-ribosyl)ation. These ADPRT mutant mice were viable and fertile indicating that ADPRT is dispensable in mouse development. Moreover, repair of UV and MNNG induced DNA damage was not affected in ADPRT/3T3 like fibroblasts, as measured by reactivation of in vitro damaged reporter plasmids and unscheduled DNA synthesis. However, about 30% of the ADPRT mutant mice developed pathological skin aberrations on a mixed 129/Sv x C57B1/6 genetic background. These mice will be extremely useful to define the precise biological role of poly(ADP-ribosyl)ation.

Regulation of the human poly(ADP-ribosyl) transferase promoter via alternative DNA racket structures

Human nuclear poly(ADP-ribosyl) transferase (ADPRT) protein content in cells suggests that ADPRT expression is stringently controlled. Analysis of the 3 kb promoter sequence, which is required for high level expression, revealed an extraordinary architecture: several Sp1 motifs are located in the vicinity of the first exon but the closest CCAAT/TATA boxes are several hundred basepairs away. Four Alu type repetitive sequences are in the promoter structure. Within these Alu sequences there exist inverted repeat elements, which could form two mutually exclusive types of DNA tertiary structure consisting of quadruplex DNA and loops resembling rackets. Thereby, a CCAAT/TATA element would be moved to spatial vicinity of the Sp1 site activating the promoter. Deletion analysis showed the functional significance of these racket elements. We also obtained evidence for DNA racket structures when we studied mutational mechanisms in a human adenine phosphoribosyltransferase (APRT) deficient patient. One of his alleles harbours a novel complex type of deletion/insertion mutation. Based on several highly informative sequence features in this genomic region a model is proposed for the generation of this unusual type of mutation involving two steps: an initial targeting step and a subsequent complex rearrangement. This process includes the formation of a DNA racket structure, which resembles that of the ADPRT promoter. Thus we conclude that DNA racket structures seem to be of general importance in nature.

Transcriptional regulation and autoregulation of the human gene for ADP-ribosyltransferase

Human nuclear poly(ADP-ribosyl)transferase (ADPRT) modifies proteins with branched ADP-ribose-polymers. Various proteins, including ADPRT itself, serve as acceptors for polyADP-ribose. Target proteins include those controlling basic cellular processes such as DNA repair, differentiation and proliferation. Because of the outstanding features of this enzyme: automodification, several functional domains and central role in physiology of the cell, the molecular biology of ADPRT gained wide interest. The promoter structure contains several CCAAT/TATA boxes and SP1 sites. However, there is no CCAAT/TATA box in the neighbourhood of an SP1 site and, thus no obvious site for initiation of transcription. Within this region there are several noteworthy inverted repeats, which by internal basepairing could form two types of cruciform structures. Deletion analysis revealed that these cruciform structures have functional significance. Removal of one type increases the promoter activity, whereas removal of the other diminishes the promoter function. Overexpression of ADPRT from heterologous promoters (MMTV, SV40) leads to repression of the activity of the ADPRT promoter. Indeed, ADPRT was shown to bind specifically to one type of cruciform structure. This specific interaction indicates autorepression of the ADPRT gene: the enzyme ADPRT acts directly as a negative modulator of the activity of its own promoter.

The immunosuppressive substance 2-chloro-2-deoxyadenosine modulates lipoprotein metabolism in a murine macrophage cell line (P388 cells)

A recently developed immunosuppressive substance, 2-chloro-2-deoxyadenosine (2-CdA), was reported to inhibit monocyte functions at low concentration. Because macrophages play a key role in the formation of atherosclerotic plaques, it was of interest to study the effect of 2-CdA on cellular lipid metabolism. For this purpose we have used a macrophage cell line (P388) to perform incubation studies in the presence of acetylated low density lipoprotein (Ac-LDL) and 2-CdA. The addition of 2-CdA, in concentrations ranging from 5-20 nM, induced a dose-dependent decrease in cellular cholesterol content and in the amount of extracellular [14C]oleic acid (OA) incorporated into the cholesteryl ester (CE) fraction. The effect was maximized at 20 nM 2-CdA with an 86% reduction in cholesterol esterification compared to controls (P < 0.008). To evaluate the mechanism of interaction of 2-CdA with cellular lipid metabolism, deoxycytidine (dCyt) and 3-methoxybenzamide (3-MOB), substances known to antagonize the effect of 2-CdA in different ways, were co-administered with 2-CdA. dCyt, a competitive inhibitor of dCyt kinase, which catalyzes phosphorylation to the active metabolite, antagonized the effects of 20 nM 2-CdA, producing significantly greater incorporation of extracellular [14C]OA into the CE fraction than in the presence of 2-CdA alone (P < 0.0086). Co-incubation with 2-CdA and the poly-ADP-ribose synthetase inhibitor 3-MOB, which is known to render cells resistant to 2-CdA toxicity by preventing cellular nicotinamide adenine dinucleotide (NAD)- and adenosine triphosphase-depletion, also reversed the effect of 2-CdA on lipid accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The human ubiquitin-conjugating enzyme UbcH1 is involved in the repair of UV-damaged, alkylated and cross-linked DNA

The human ubiquitin-conjugating enzyme UbcH1 shows 69% identity to the Saccharomyces cerevisiae RAD6/UBC2 which plays a key role in DNA repair. To examine the function of UbcH1 (formerly named E2, M(r) 17,000), [(1990) EMBO J. 9, 1431-1435]) we tested its ability to functionally substitute for yeast RAD6/UBC2 in the recovery of cells from various DNA damage. Complementation by expression of the human UbcH1 cDNA revealed that the UbcH1 carries out the function of S. cerevisiae RAD6/UBC2 in the repair of UV-damaged, alkylated and cross-linked DNA.

Effect of transfection of human poly(ADP-ribose)polymerase in Chinese hamster cells on mutagen resistance

Poly(ADP-ribose)polymerase (PARP) is a DNA-binding protein that is activated upon induction of DNA breaks and supposed to play a role in DNA repair. To elucidate the effect of overexpression of PARP on the resistance of cells to mutagens, Chinese hamster ovary cells (both the line CHO-9 and the mutagen-hypersensitive derivative 27-1) were transfected with the human PARP cDNA along with pSV2neo. Treatment of the transfected cell population with a high dose of MNNG and selection with G418 gave rise to a significant increase of neo+ clones, as compared to the control transfection with pSV2neo + salmon sperm DNA. The frequency of survivors in these mass culture experiments was lower, however, than after transfection with the bacterial ada gene encoding the DNA repair protein O6-alkylguanine-DNA alkyltransferase. Thus transfection of PARP cDNA in CHO cells is only weakly effective in inducing alkylation resistance. This was confirmed by analyzing the mutagen resistance of individual PARP transfectant clones derived from CHO-9 and 27-1 cells that expressed increased levels of PARP mRNA, protein and PARP activity. These strains were slightly more resistant to the toxic effect of MMS and showed a reduced frequency of MMS-induced chromosomal aberrations. CHO-9-PARP transfectants also gained resistance to UV. From these data we conclude that, in CHO cells, PARP is limiting in handling critical lesions during the repair process and that increase of the amount of PARP protein can elicit some protection against genotoxic effects of mutagens.

Purification and characterization of NAD+:ADP-ribosyltransferase (polymerizing) from Dictyostelium discoideum

A novel affinity-purification scheme based on the tight binding of NAD+:ADP-ribosyltransferase (polymerizing) [pADPRT; poly(ADP-ribose) polymerase; EC 2.4.2.30] to single-strand nicks in DNA, single-stranded patches and DNA ends has been developed to facilitate the purification of this enzyme from the lower eukaryote Dictyostelium discoideum. Two homogeneous forms of the enzyme, with M(r) values of 116,000 and 90,000, were prepared from D. discoideum by using poly(A) hybridized to oligo(dT)-cellulose as affinity material. The Km is 20 microM NAD+ for the 90,000-M(r) protein and 77 microM NAD+ for the 116,000-M(r) protein. The optimum conditions for the enzyme activity in vitro are 6-10 degrees C and pH 8. The time course is linear during the first 10 min of the reaction only. As in enzymes of higher eukaryotes, the activity is dependent on DNA and histone H1 and is inhibited by 3-methoxybenzamide, nicotinamide, theophylline, caffeine and thymidine.

Polyclonal antibody-based immunoradiometric assay for quantification of cholesteryl ester transfer protein

Cholesteryl ester transfer protein (CETP) catalyzes the transfer of neutral lipids among plasma lipoproteins and in this way plays a prominent role in cholesterol metabolic routing and, thus, probably for atherosclerosis. Studies of this important protein in various clinical settings require the ability to accurately quantify CETP in plasma. In order to gain access to such a capability, an immunoradiometric assay (IRMA) for quantification of CETP was developed. CETP was purified from human plasma to apparent homogeneity and used for raising anti-CETP antibodies in rabbits. The specificity of the polyclonal antiserum obtained was demonstrated by inhibition assays and immunoblot analysis. Before use in the CETP-IRMA, the antibodies were affinity-purified by chromatography on CETP-Sepharose. Sensitivity of the CETP-IRMA was 0.1 ng, and intra- and interassay coefficients of variation were 2.9 and 8.0%, respectively. In 30 normolipidemic healthy subjects, the mean (+/- SD) CETP concentration was 1.1 (+/- 0.22) micrograms/ml of plasma; individual values ranged from 0.644 to 1.694 micrograms CETP/ml and agreed well with measurements of CETP activity of the same samples (r = 0.85).

Genomic organization, localization, and allelic differences in the gene for the human neuropeptide Y Y1 receptor

A 14-kilobase pair (kb) region of genomic DNA encoding the human neuropeptide Y Y1-receptor gene including 3'- and 5'-flanking sequences has been cloned and the human gene localized to chromosome 4q(31.3-32). In contrast to the contiguous structure of most G protein-coupled receptor genes, the NPY Y1 receptor gene is divided into three exons. A small 5'-exon of the mRNA untranslated region is separated by a 6-kb intron from the second exon. The coding region of the receptor is interrupted by a small intron, containing an in-frame stop codon, shortly after the proposed fifth transmembrane domain. In the 5'-flanking region a potential cAMP-response element and an AP-2 site, in addition to a TATA-like sequence and a typical CAAT, box are present. A single point mutation within the 6-kb intron generates a PstI polymorphic site with a highly informative allele frequency of 54:46% in the population.

Inhibition of cell proliferation in Saccharomyces cerevisiae by expression of human NAD+ ADP-ribosyltransferase requires the DNA binding domain ("zinc fingers")

Constitutive expression of human nuclear NAD+: protein ADP-ribosyltransferase (polymerizing) [pADPRT; poly(ADP-ribose)polymerase; EC 2.4.2.30] as an active enzyme in Saccharomyces cerevisiae, under the control of the alcohol dehydrogenase promoter, was only possible with simultaneous inhibition of ADP-ribosylation by 3-methoxybenzamide. Induction of fully active pADPRT from the inducible galactose epimerase promoter resulted in inhibition of cell division and morphological changes reminiscent of cell cycle mutants. Expression of a pADPRT cDNA truncated at its 5' end had no influence on cell proliferation at all. Obviously the amino-terminal part of the DNA binding domain containing the first "zinc finger", which is essential for inducibility of pADPRT activity by DNA breaks, is also required for inhibition of cell growth on expression in yeast. Full-length as well as truncated pADPRT molecules were directed to the cell nucleus where the fully active enzyme produced large amounts of poly(ADP-ribose) by automodification. Since pADPRT turned out to be the only target for ADP-ribosylation in these cells, elevated levels of poly(ADP-ribose) were the most likely cause of inhibition of cell division, presumably resulting from interaction with chromosomal proteins.

Fluorescence in situ mapping of the human nuclear NAD+ ADP-ribosyltransferase gene (ADPRT) and two secondary sites to human chromosomal bands 1q42, 13q34, and 14q24

A 3.5-kb cDNA probe containing the 23 exons from the coding sequence of human nuclear NAD+ ADP-ribosyltransferase (poly [ADP-ribose] polymerase [ADPRT], E.C.2.4.2.30) was used to map the gene and two additional sites by nonisotopic in situ chromosomal hybridization. The previous localization of the structural gene on 1q42 was confirmed. Two other hybridization peaks on 13q34 and 14q24 suggested the presence of ADPRT pseudogenes.

Primary structure of a DNA (N6-adenine)-methyltransferase from Escherichia coli virus T1. DNA sequence, genomic organization, and comparative analysis

Escherichia coli virus T1 encodes a DNA (N6-adenine)-methyltransferase (M.T1) with the same sequence specificity as the E. coli DNA (N6-adenine)-methyltransferase (M.Eco dam). This enzyme was purified to homogeneity and a partial amino acid sequence determined. Oligonucleotides were constructed and used not only as probes to map the gene on the T1 genome, but also as primers in sequencing reactions to establish the nucleotide sequence of the M.T1 locus by primer extension. These data represent the first analysis of the genomic organization of bacterial virus T1 on a molecular level. Significant homology to E. coli consensus transcription and translation-initiation signals suggest that the gene for M.T1 is most probably under control of its own promoter. It may be transcribed as a polycistronic mRNA, together with a downstream open reading frame which codes for a polypeptide containing 83 amino acids (HP 83). Both the deduced primary and the secondary structure of the M.T1 were compared to those of other known DNA methyltransferases, especially those recognizing the sequence, GATC; there is little similarity of the T1 enzyme to the other members of this family.

Effects of haloperidol and clozapine on preprotachykinin-A messenger RNA, tachykinin tissue levels, release and neurokinin-1 receptors in the striato-nigral system

The effects of haloperidol and clozapine on tachykinin tissue levels, preprotachykinin-A messenger RNA, spontaneous and potassium-evoked tachykinin release, dopamine D2 receptors, and [125I]Bolton-Hunter-substance P binding sites in the striato-nigral system were examined. Chronic administration (10 days) of the dopamine receptor antagonist haloperidol (2 mg/kg i.p.) significantly decreased tissue levels of substance P like-immunoreactivity and neurokinin A like-immunoreactivity in the striatum and the substantia nigra. The corresponding preprotachykinin-A mRNA was decreased in the striatum. Haloperidol did not affect the potassium-evoked tachykinin release in the substantia nigra but significantly increased the spontaneous release. Haloperidol increased the number of D2-receptors but left [125I]Bolton-Hunter-substance P binding sites, representing neurokinin 1 (NK-1) receptors, as determined by competition experiments with selective ligands, unchanged. Clozapine (30 mg/kg, i.m.) did not influence nigral and striatal tachykinin tissue levels, preprotachykinin-A mRNA and potassium-evoked release or spontaneous efflux in the substantia nigra, or D2-receptors and [125I]Bolton-Hunter-substance P binding sites. The present data indicate that neuroleptics influence the striato-nigral tachykinin system in different ways. Tachykinins may, therefore, contribute to the therapeutic and/or untoward effects of certain neuroleptic drugs.

Human nuclear NAD+ ADP-ribosyltransferase(polymerizing): organization of the gene

Human nuclear NAD+: protein ADP-ribosyltransferase(polymerizing) [pADPRT; poly(ADP-ribose)poly-merase; EC 2.4.2.30] is a DNA-dependent protein-modifying enzyme composed of several domains important for DNA binding, automodification, and NAD binding. We report that the human pADPRT gene is 43 kb in length and is split into 23 exons. All the intron-exon boundaries correspond to a canonical splice consensus sequence. Each of the four metal coordinating sites putatively forming the two zinc fingers of the DNA-binding domain is encoded separately. The automodification domain and the NAD-binding domain are coded for by 4 and 12 exons, respectively.

Human nuclear NAD+ ADP-ribosyltransferase: localization of the gene on chromosome 1q41-q42 and expression of an active human enzyme in Escherichia coli

The gene for human nuclear NAD+ ADP-ribosyltransferase [NAD+:poly(adenosine diphosphate D-ribose) ADP-D-ribosetransferase, EC 2.4.2.30; pADPRT] was localized to chromosome 1 at q41-q42 by in situ hybridization with a pADPRT-specific cDNA probe. Expression of a pADPRT cDNA under control of the lac promoter in Escherichia coli induces the synthesis of a group of related proteins that were immunoreactive with pADPRT antibody and that had catalytic properties very similar to those of the human enzyme. Purification of this enzymatic activity was performed essentially as described for the human enzyme. The Km, pH optimum, optimal reaction temperature, and inhibition by 3-aminobenzamide and 3-methoxybenzamide were found to be similar for the recombinant and the human enzymes. The purified recombinant enzyme consists of two major proteins of Mr 99,000 and Mr 89,000. Both proteins show pADPRT activity in activity gel analysis with [32P]NAD+ as substrate. Microsequencing of these two proteins isolated by denaturing gel electrophoresis and deletion mutagenesis of the pADPRT expression plasmid shows that the Mr 99,000 and Mr 89,000 proteins derive from initiation of translation at internal translational start signals located within the pADPRT cDNA.

L-carnitine substitution in patients on chronic hemodialysis

Patients on chronic hemodialysis with hyperlipidemia were found to respond either with decreased levels (responders) or with a further increase of the plasma triglyceride levels (nonresponders) to a carnitine substitution therapy. The aim of the present study was to find possible predictors to distinguish between responders and nonresponders prior to the initiation of therapy. Since it is suggested that erythrocytes are involved in carnitine transport to tissues, it was of interest to determine plasma and erythrocyte carnitine concentrations in the hemodialyzed patients before and during carnitine substitution therapy and to compare the results with those of healthy controls. Before therapy, comparatively lower plasma levels of both free and total carnitine, but higher portions of short-chain acylcarnitine on total carnitine were found in all patients. In erythrocytes, the nonresponders showed significantly higher total carnitine levels, compared to responders and controls. After the start of carnitine substitution, the increase of total plasma carnitine during the substitution period corresponded with the carnitine dose administered in responders, in nonresponders the highest carnitine values were found in the second week when the lower carnitine dose was administered. The changes of the plasma short-chain acylcarnitine levels with time were very similar to those of plasma triglycerides. All patients showed a time-delayed accumulation of carnitine in erythrocytes and, interestingly, markedly higher concentrations in the second week when the lower carnitine dose was administered. The results of the present study demonstrate that the erythrocyte carnitine content is a reliable predictor to distinguish between responders and nonresponders prior to the start of a carnitine substitution therapy.

The primary structure of human ribonuclease/angiogenin inhibitor (RAI) discloses a novel highly diversified protein superfamily with a common repetitive module

Immunological screening of a lambda gt11 library, constructed from HeLa mRNA, yielded several ribonuclease/angiogenin inhibitor (RAI) cDNA clones containing 900-bp inserts. Northern blot analysis revealed that the length of the RAI mRNA is approximately 1.9 kb. Construction and screening of a eukaryotic cDNA expression library (HeLa) containing preferentially complete cDNA inserts led to the isolation of a full length clone. The complete nucleotide sequence was determined. The C-terminal amino acid sequence deduced from the cDNA is identical to the peptide sequence obtained from a CNBr fragment of RAI, confirming the identity of the clone. The deduced primary structure of RAI consists of eight homologous tandem repeats with remarkable periodicity of leucine and cysteine residues. Each repeat is derived from the duplication of a leucine-rich 28-amino-acid module. This prototype module is closely related to a repetitive 24-amino-acid motif of unclear function, previously found in proteins involved in important biological processes such as blood coagulation, embryonic development, cell morphogenesis and signal transduction. Although homologous, the RAI modules show distinct differences in length and amino acid composition to the modules of this group of proteins, demonstrating their high potential of variability, necessary for adaptation to very diverse roles. Based on our results we propose that these repetitive modules are a common structural feature of a novel protein superfamily whose members exert their function by highly specific protein-protein interactions.

ADP-ribosylation in isolated nuclei of Physarum polycephalum

ADP-ribosylation of histones and non-histone nuclear proteins was studied in isolated nuclei during the naturally synchronous cell cycle of Physarum polycephalum. Aside from ADP-ribosyltransferase (ADPRT) itself, histones and high mobility group-like proteins are the main acceptors for ADP-ribose. The majority of these ADP-ribose residues is NH2OH-labile. ADP-ribosylation of the nuclear proteins is periodic during the cell cycle with maximum incorporation in early to mid G2-phase. In activity gels two enzyme forms with Mr of 115,000 and 75,000 can be identified. Both enzyme forms are present at a constant ratio of 3:1 during the cell cycle. The higher molecular mass form cannot be converted in vitro to the low molecular mass form, excluding an artificial degradation during isolation of nuclei. The ADPRT forms were purified and separated by h.p.l.c. The low molecular mass form is inhibited by different ADPRT inhibitors to a stronger extent and is the main acceptor for auto-ADP-ribosylation. The high molecular mass form is only moderately auto-ADP-ribosylated.

ADP-ribosyltransferase from Helix pomatia. Purification and characterization

ADP-ribosyltransferases from several higher eukaryotes have been purified and characterized, but little is known about ADP-ribosyltransferases in lower eukaryotes. We have purified an ADP-ribosyltransferase (EC 2.4.2.30) from Helix pomatia. The enzyme has an apparent Km of 26.7 microM. Optimal conditions for the enzyme reaction are 17.5 degrees C and pH 8. The time course is linear during the first 10 min of the reaction. The enzyme is capable of poly-ADP-ribosylation. The most highly purified preparation shows one major band at an Mr of 75,000 on electrophoresis in an SDS/polyacrylamide gel, with minor bands at Mr 115,000 and 155,000. Re-activation of SDS/polyacrylamide gels in situ shows the 75,000-Mr band to be enzymically active and additional active bands with Mr values of 115,000, 90,000 and 87,000 respectively. The 115,000-Mr and 75,000-Mr bands cross-react with a polyclonal affinity-purified antiserum against human ADP-ribosyltransferase. Like enzymes from higher eukaryotes, the activity from Helix pomatia is inhibited by thymidine, theophylline, theobromine nicotinamide, 3-methoxybenzamide and 3-aminobenzamide, and is dependent on histone and DNA.