Nicotinamide mononucleotide adenylyl transferase (NMNAT) is an essential enzyme in all organisms, because it catalyzes a key step of NAD synthesis. However, little is known about the structure and regulation of this enzyme. In this study we established the primary structure of human NMNAT. The human sequence represents the first report of the primary structure of this enzyme for an organism higher than yeast. The enzyme was purified from human placenta and internal peptide sequences determined. Analysis of human DNA sequence data then permitted the cloning of a cDNA encoding this enzyme. Recombinant NMNAT exhibited catalytic properties similar to the originally purified enzyme. Human NMNAT (molecular weight 31 932) consists of 279 amino acids and exhibits substantial structural differences to the enzymes from lower organisms. A putative nuclear localization signal was confirmed by immunofluorescence studies. NMNAT strongly inhibited recombinant human poly(ADP-ribose) polymerase 1, however, NMNAT was not modified by poly(ADP-ribose). NMNAT appears to be a substrate of nuclear kinases and contains at least three potential phosphorylation sites. Endogenous and recombinant NMNAT were phosphorylated in nuclear extracts in the presence of [Q Q-32 P]ATP. We propose that NMNAT's activity or interaction with nuclear proteins are likely to be modulated by phosphorylation. ß 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

The epigenetic sensor BRD4 (bromodomain protein 4) is a potent target for anti-cancer therapies. To study the transcriptional impact of BRD4 in cancer, we generated an expression signature of BRD4 knockdown cells and found oxidative stress response genes significantly enriched. We integrated the RNA-Seq results with DNA-binding sites of BRD4 generated by chromatin immunoprecipitations, correlated these with gene expressions from human prostate cancers and identified 21 top BRD4 candidate genes among which the oxidative stress pathway genes KEAP1, SESN3 and HDAC6 are represented. Knock down of BRD4 or treatment with the BRD4 inhibitor JQ1 resulted in decreased reactive oxygen species (ROS) production and increased cell viability under H2O2 exposure. Consistently, a deregulation of BRD4 diminished the KEAP1/NRF2 axis and led to a disturbed regulation of the inducible heme oxygenase 1 (HMOX1). Without exogenous stress induction, we also found BRD4 directly targeting the HMOX1 promoter over the SP1-binding sites. Our findings provide insight into the transcriptional regulatory network of BRD4 and highlight BRD4 as signal transducer of the cellular response to oxidative stress.

Adult T cell leukemia derived factor (ADF)/thioredoxin (Trx) is known to be an important intracellular antioxidant involved in a number of redox reactions such as ribonucleotide reductase (RNR) as well as of tyrosinase. Since RNR is a key enzyme of nucleotide metabolism and DNA synthesis, a reduced Trx level would result in reduced enzymatic activity and cause DNA damage. Furthermore, Trx is considered to be an effective regulator of redox sensitive gene expression. The role of Trx in nucleotide metabolism and gene expression may be an explanation for increased chromosomal instability as well as hypersensitivity towards oxygen, ROI and ROI generating agents. The activity of tyrosinase, the key enzyme of melanin biosynthesis, is influenced by the thioredoxin level and by superoxide radicals. Low thioredoxin levels and high superoxide concentrations activate tyrosinase causing hyperpigmentation of the skin. In addition to the observed high superoxide concentration in Fanconi anemia (FA) patients, a low thioredoxin level might be responsible for the hyperpigmentation (cafe è-aulait spots) in this disease. We observed that overexpression of the thioredoxin cDNA in FA fibroblasts completely abolished the DNA damaging effects of mitomycin C and diepoxybutane and inhibited the constitutive activity of the nuclear factor U UB (NF-U UB) in SV40 transformed FA fibroblasts. However, spontaneous chromosomal breakage was not affected.z 1998 Federation of European Biochemical Societies.

The molecular defect of the hereditary disease Fanconi anemia (FA) remains unknown. The two theoretical possibilities are (1) an impaired DNA crosslink-repair system or (2) a disturbed oxygen metabolism either by overproduction of reactive oxygen intermediates (ROI) or by diminished detoxification of ROI. In order to gain further insight into the molecular mechanism of this disease, we have determined the repair capacity of FA cells challenged by crosslinking agents and have analyzed diverse biological systems that are involved in oxygen metabolism. We have tested normal and FA cells for oxygen consumption and for the activity of the antioxidant phospholipid-hydroperoxide-glutathione-peroxidase (PHGPx). FA cells show a reduced oxygen consumption and an increased PHGPx activity. Since spontaneous and induced chromosomal instability is a main cellular feature of FA, we have analyzed the redox state of cells and the effect of cytochrome P-450 (Cyt P-450) inhibitors and inducers on chromosomal breaks and micronuclei production. Our results indicate that Cyt P-450 enzymes, especially Cyt P-450 1A2, play a crucial role in radical metabolism in FA cells. Furthermore, we have determined NF-kappa B activity in untransformed cells and in SV40-transformed cells by gel shift experiments. NF-kappa B is a multiunit transcription factor that is known to be induced by ROI and that activates the expression of various genes involved in cellular responses to stress. NF-kappa B is constitutively induced in SV40-transformed FA cells probably as a consequence of an increased ROI level. Our results suggest that enzymatic defects in oxygen metabolism mediate the FA phenotype via impaired reactivity with ROI. Cyt P-450 1A2 appears to be a good candidate for the defective enzyme, even though no differences have been measured in the activity of this enzyme in FA and control fibroblasts in pilot experiments.

After infection with bacteriophage T7 the ft' and to a lesser extent the , subunits of E. coli DNA-dependent RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) are phosphorylated by a phagegene-encoded protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37). The phosphorylation occurs on threonine residues and appears site-specific. It (v/v) glycerol] were applied as bands of about 0.75 cm width. Staining and destaining were as described in Heil and Zillig (6); Cellogel strips (Chemetron, Milano) were dried as described in the recipe leaflet of Chemetron.