Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

NAD(P)H: quinone oxidoreductase (NQO1) is believed to be protective against cancer and toxicity caused by exposure to quinones and their metabolic precursors. This enzyme catalyzes the two-electron reduction of compounds, compared with one-electron reduction mediated by NADPH: cytochrome-P450 oxidoreductase which produces toxic and mutagenic free radicals. Recently we cloned and sequenced the cDNA encoding human 2.3,7,8-tetrachlorodibenzo-p-dioxin (dioxin)-inducible cytosolic NQO1 [Jaiswal et al. (1988) J. Biol. Chem. 263, 13572-13578] and provided preliminary evidence that this enzyme may correspond to diaphorase 4, an enzymatic activity present in various tissues that catalyzes the reduction of a variety of quinones by both NADH and NADPH [Edwards et al. (1980) Biochem. J. 187, 429-436]. In the present report we characterize the catalytic properties of the protein encoded by the NQO1 cDNA. The enzyme was synthesized in monkey kidney COS-1 cells transfected with a pMT2-based expression plasmid containing the NQO1 cDNA. Western blot analysis of the transfected cells using an antibody against rat liver cytosolic NQO1 revealed a 31-kDa band that was not detected in nontransfected cells. This band corresponded to a polypeptide with the same electrophoretic mobility as the endogenous NQO1 protein detected in the human hepatoblastoma (Hep-G2) cells with the same antibody. The immunoreactive protein detected in human Hep-G2 cells was induced approximately fourfold by exposure of the cultures to dioxin, an increase commensurate with the increased in quinone oxidoreductase activity. These studies suggest that the protein encoded by NQO1 cDNA is indeed similar, if not identical, to the dioxin-inducible protein band detected in human Hep-G2 cells. Further characterization of the product of NQO1 cDNA, which was present at approximately 20-30-fold higher levels in transfected COS cells than the endogenous product in uninduced human Hep-G2 cells indicated that it had very high capacity (greater than 1000-fold over background) to catalyze the reduction of 2.6-dichloroindophenol and menadione. Besides these two commonly used substrates for quinone reductase, the expressed NQO1 protein also effectively metabolized 2,6-dimethylbenzoquinone, methylene blue, p-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-benzoquinone, with the latter being the most potent electron acceptor at 50 microM concentration of the substrate.
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PMID:The human dioxin-inducible NAD(P)H: quinone oxidoreductase cDNA-encoded protein expressed in COS-1 cells is identical to diaphorase 4. 189 80

Human breast (MCF-7, HBL 100, T47D, BT20, HS578T), colon (HT29, CACO2, SW620, SW480, COLO320DM) and small cell lung cancer (NCI-N417, OH3, SW2) cell lines were transplanted subcutaneously into severe combined immunodeficient (SCID) mice. When sizeable tumours developed, the mice were sacrificed and the following enzyme activities were detected histochemically: presumed nitric oxide synthase-associated diaphorase (NOSaD), beta-D-glucuronidase (beta-Gluc) and non-specific alkaline phosphatase (alP). Except for HT29 and MCF-7 presumed NOSaD activity was not detected in the tumour itself or in the neo-vasculature of the tumours. beta-Gluc activity was found in all tumour cells (except N417 and COLO 320), in the necrotic parts of the tumours and in stromal cells of the tumour bed. AlP activity was present in all tumours including their necrotic areas. However, the activities of beta-Gluc and alP varied considerably even within one tumour, ranging from very weak to very strong. Principally the results show that the human/SCID mouse tumour model is well suited to test modern applications of tumour therapy involving the enzymes NOSaD, beta-Gluc and alP. In particular, antibody directed enzyme prodrug therapy concepts and activation of prodrugs by enzymes released from tumour cells into the necrotic areas of the tumour can be evaluated in this in vivo model.
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PMID:Histochemistry of therapeutically relevant enzymes in human tumours transplanted into severe combined immunodeficient (SCID) mice: nitric oxide synthase-associated diaphorase, beta-D-glucuronidase and non-specific alkaline phosphatase. 896 Mar 2

The objective of this study was to identify pathways that regulate the cytotoxicity induced by free fatty acids (FFAs) in human hepatoblastoma cells (HepG2/C3A). Gene expression profiles of HepG2/C3A cells were obtained at three time points, after 24, 48, and 72 h of exposure to different types of FFA. Saturated fatty acid (palmitate) was found to be cytotoxic. The pathways activated by the different FFAs at the different time points were identified using global gene module map analysis. Unsaturated FFAs exerted transcriptional regulation mainly within the first 24 h, whereas saturated FFA, palmitate, regulated energy production pathways, such as the electron transport chain (ETC) and tricarboxylic acid cycle, within the first 24 h. In the next 24 h, palmitate up-regulated 36 cell death relevant pathways and down-regulated several protective pathways, such as the pentose phosphate pathway and glutathione-related pathways. In the final 24 h, the FFAs did not induce significant transcriptional regulation. We hypothesized that palmitate induced cytotoxicity by first perturbing metabolic pathways in the initial 24 h, resulting in changes to factors, such as metabolites or signaling molecules, which subsequently triggered cell death relevant pathways in the next 24 h. The uptake and release of 27 metabolites were measured to further elucidate the metabolic changes in the first 24 h. It was determined that ketone bodies such as beta-hydroxybutyrate and acetoacetate were important in separating the toxic from the nontoxic phenotypes. A regression model was used to identify the genes relevant to these metabolites. Some of the genes identified to be important were experimentally validated. It was found that ETC genes such as NADH dehydrogenase and succinate dehydrogenase were involved in palmitate induced cytotoxicity.
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PMID:Using dynamic gene module map analysis to identify targets that modulate free fatty acid induced cytotoxicity. 1805 88