Biomedical subjects

Philip J Moos

Publications and source records attributed to Philip J Moos.

7 recordsLinked to original sources

PubMed2006

Thioredoxin reductase is required for the inactivation of tumor suppressor p53 and for apoptosis induced by endogenous electrophiles.

Previous studies demonstrate that the covalent modification of thioredoxin reductase (TrxR) by both endogenous and exogenous electrophiles results in disruption of the conformation of the tumor suppressor protein p53. Here we report that the loss of normal cellular TrxR enzymatic activity by electrophilic modification or deletion of the C-terminal catalytic selenocysteine residue has functional consequences that are distinct from those resulting from depletion of TrxR protein in human RKO colon cancer cells. A thorough kinetic analysis was performed on purified TrxR in order to characterize the mechanism of its inhibition by electrophiles. Furthermore, electrospray mass spectrometry confirmed the alkylation of TrxR by lipid electrophiles and liquid chromatography-mass spectrometry/mass spectrometry identified the C-terminus as one target for alkylation. Then the consequences of TrxR modification by electrophiles on p53 conformation, transactivation and apoptosis were compared and contrasted with the effects of depletion of TrxR protein by treatment of cells with small interfering RNA directed against TrxR1. We found that cells depleted of TrxR were actually less sensitive to electrophile-induced disruption of p53 conformation and apoptosis than were cells expressing normal levels of TrxR. When RKO cells depleted of wild-type TrxR were transfected with C-terminal mutants of TrxR lacking the catalytic selenocysteine, p53 was found to be conformationally deranged, similar to cells treated with electrophiles. These results lead us to conclude that C-terminal modification of TrxR is both necessary and sufficient for the disruption of p53 and for the induction of apoptosis. Endogenous lipid electrophiles have been our primary focus; however, metabolic activation of hormones can generate endogenous mutagens, and we demonstrate that estrone-quinone attenuates p53 function in human MCF7 cells.

Apoptosis↗

PubMed2004

Conditional expression of 15-lipoxygenase-1 inhibits the selenoenzyme thioredoxin reductase: modulation of selenoproteins by lipoxygenase enzymes.

The selenoenzyme thioredoxin reductase regulates redox-sensitive proteins involved in inflammation and carcinogenesis, including ribonucleotide reductase, p53, NFkappaB, and others. Little is known about endogenous cellular factors that modulate thioredoxin reductase activity. Here we report that several metabolites of 15-lipoxygenase-1 inhibit purified thioredoxin reductase in vitro. 15(S)-Hydroperoxy-5,8,11-cis-13-trans-eicosatetraenoic acid, a metastable hydroperoxide generated by 15-lipoxygenase-1, and 4-hydroxy-2-nonenal, its non-enzymatic rearrangement product inhibit thioredoxin reductase with IC(50) = 13 +/- 1.5 microm and 1 +/- 0.2 microm, respectively. Endogenously generated metabolites of 15-lipoxygenase-1 also inhibit thioredoxin reductase in HEK-293 cells that harbor a 15-LOX-1 gene under the control of an inducible promoter complex. Conditional, highly selective induction of 15-lipoxygenase-1 caused an inhibition of ribonucleotide reductase activity, cell cycle arrest in G(1), impairment of anchorage-independent growth, and accumulation of the pro-apoptotic protein BAX. All of these responses are consistent with inhibition of thioredoxin reductase via 15-lipoxygenase-1 overexpression. In contrast, metabolites of 5-lipoxygenase were poor inhibitors of isolated thioredoxin reductase, and the overexpression of 5-lipoxygenase did not inhibit thioredoxin reductase or cause a G cell cycle arrest. The influences of 15-lipoxygenase-1 on (1)inflammation, cell growth, and survival may be attributable, in part, to inhibition of thioredoxin reductase and several redox-sensitive processes subordinate to thioredoxin reductase.

Aldehydes↗

PubMed2004

Curcumin impairs tumor suppressor p53 function in colon cancer cells.

Curcumin (diferuloylmethane) is being considered as a potential chemopreventive agent in humans. In vitro it inhibits transcription by NF-kappaB, and the activity of lipoxygenase or cyclooxygenase enzymes, which facilitate tumor progression. In vivo it is protective in rodent models of chemical carcinogenesis. Curcumin contains an alpha,beta-unsaturated ketone, a reactive chemical substituent that is responsible for its repression of NF-kappaB. In compounds other than curcumin this same electrophilic moiety is associated with inactivation of the tumor suppressor, p53. Here we report that curcumin behaves analogously to these compounds. It disrupts the conformation of the p53 protein required for its serine phosphorylation, its binding to DNA, its transactivation of p53-responsive genes and p53-mediated cell cycle arrest.

Antineoplastic Agents↗

PubMed2004

Impact of microarray technology in clinical oncology.

Genomic technologies are rapidly evolving and have demonstrated utility in augmenting oncological pathology or clinical presentation in disease classification and risk of relapse assessment. Numerous malignancies have been subject to microarray examination, and through a variety of analysis methodologies, groups of reporter genes have been identified to generate 'molecular portraits' of these diseases. Once validated, it is likely that assessment of the expression levels of subsets of reporter genes will contribute to personalized genomic medicine through diagnosis and selection of treatment options for patients. The dynamic nature of this field ensures that new developments are missing from this review.

Diagnosis, Differential↗

PubMed2002

Electrophilic prostaglandins and lipid aldehydes repress redox-sensitive transcription factors p53 and hypoxia-inducible factor by impairing the selenoprotein thioredoxin reductase.

Tumor suppressor p53 exhibits an enigmatic phenotype in cells exposed to electrophilic, cyclopentenone prostaglandins of the A and J series. Namely, cells harboring a wild-type p53 gene accumulate p53 protein that is conformationally and functionally impaired. This occurs via an unknown molecular mechanism. We report that electrophilic cyclopentenone prostaglandins covalently modify and inhibit thioredoxin reductase, a selenoprotein that governs p53 and other redox-sensitive transcription factors. This mechanism accounts fully for the unusual p53 phenotype in cells exposed to electrophilic prostaglandins. Based on this mechanism we derived, tested, and affirmed several predictions regarding the kinetics of p53 inactivation; the protective effects of selenium; the structure-activity relationships for inhibition of thioredoxin reductase and impairment of p53 by electrophilic lipids; the susceptibility of hypoxia-inducible factor to inactivation by electrophilic lipids; and the equivalence of chemical inactivation of p53 to deletion of a p53 allele. Chemical precepts dictate that other electrophilic agents should also inhibit thioredoxin reductase and impair its governance of redox-sensitive proteins. Our results provide a novel framework to understand how endogenous and exogenous electrophiles might participate in carcinogenesis; how selenoproteins and selenium might confer protection against cancer; how certain tumors might acquire their paradoxical p53 phenotype; and how chronic inflammation might heighten the risk for cancer.

Aldehydes↗

PubMed2002

Cyclooxygenase-2 induction by paclitaxel, docetaxel, and taxane analogues in human monocytes and murine macrophages: structure-activity relationships and their implications.

Paclitaxel and docetaxel can induce pro-inflammatory proteins, typified by cyclooxygenase-2 (prostaglandin H synthase). In some circumstances, this phenomenon may be relevant to the immunomodulatory actions and the adverse effects associated with paclitaxel or docetaxel. Accordingly, we compared a panel of sixteen taxanes, including paclitaxel and docetaxel, for their ability to induce cyclooxygenase-2 in a murine macrophage cell line (RAW 264.7) and in human peripheral blood monocytes. We discovered that the structure-activity relationships governing the induction of cyclooxygenase-2 protein differ markedly between the two species. Of 14 analogues evaluated, only 2 had activity comparable with paclitaxel in RAW 264.7 cells. In contrast, docetaxel and 12 of 14 analogues had activity comparable with paclitaxel in human monocytes. Our results enabled us to predict and subsequently affirm that the major human hepatic metabolite, 6alpha-hydroxypaclitaxel, would induce cyclooxygenase-2 in human cells but not in murine cells. Our structure-activity data and our experiments with combinations of taxanes suggest a provisional model for cyclooxygenase-2 induction. This model suggests that binding at a high-affinity site on tubulin and stabilization of microtubules is necessary, but not sufficient, for cyclooxygenase-2 induction. Binding at a second, lower-affinity receptor site is also necessary. However, our structure activity data are not fully compatible with two candidate proteins currently proposed as the low-affinity receptor.

Animals↗

PubMed2002

Identification of gene expression profiles that segregate patients with childhood leukemia.

To identify genes whose expression correlated with biological features of childhood leukemia, we prospectively analyzed the expression profiles of 4608 genes using cDNA microarrays in 51 freshly processed bone marrow samples from children with acute leukemia, over a 24-month period, at a single institution. Two supervised methods of analysis were used to identify the 20 best discriminating genes between the following cohorts: acute myelogenous leukemia (AML) versus acute lymphoblastic leukemia (ALL); B-lineage versus T-lineage ALL; newly diagnosed B-lineage standard-risk versus high-risk ALL; and B-lineage leukemia harboring the TEL-AML 1 fusion versus patients without a molecularly characterized translocation. These methods identified overlapping sets of genes that segregated patients within described subgroups. Cross-validation demonstrated that the majority of patients could be correctly classified based on these genes alone, and hierarchical clustering grouped patients with similar clinical and biological disease features. The potential for select genes to discriminate patients was validated using real-time PCR in samples that were analyzed by microarray profiling and in other uniformly processed leukemic marrow samples. As expected, microarray technology can successfully segregate patients defined by traditional measures such as immunophenotype and cytogenetic alterations. However, among specific subgroups, this preliminary analysis also suggests that microarrays can identify unanticipated similarities and diversity in individual patients and thus may be useful in augmenting risk-group stratification in the future.

Child↗