Efavirenz as a potential drug for the treatment of triple-negative breast cancers.

PURPOSE: In contrast to hormone receptor driven breast cancer, patients presenting with triple-negative breast cancer (TNBC) often have limited drug treatment options. Efavirenz, a non-nucleoside reverse transcriptase (RT) inhibitor targets abnormally overexpressed long interspersed nuclear element 1 (LINE-1) RT and has been shown to be a promising anticancer agent for treating prostate and pancreatic cancers. However, its effectiveness in treating patients with TNBC has not been comprehensively examined. METHODS: In this study, the effect of Efavirenz on several TNBC cell lines was investigated by examining several cellular characteristics including viability, cell division and death, changes in cell morphology as well as the expression of LINE-1. RESULTS: The results show that in a range of TNBC cell lines, Efavirenz causes cell death, retards cell proliferation and changes cell morphology to an epithelial-like phenotype. In addition, it is the first time that a whole-genome RNA sequence analysis has identified the fatty acid metabolism pathway as a key regulator in this Efavirenz-induced anticancer process. CONCLUSION: In summary, we propose Efavirenz is a potential anti-TNBC drug and that its mode of action can be linked to the fatty acid metabolism pathway.

Genomic innovations, transcriptional plasticity and gene loss underlying the evolution and divergence of two highly polyphagous and invasive Helicoverpa pest species.

BACKGROUND: Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests. RESULTS: We find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes. CONCLUSIONS: The extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera's invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant.

Activation of LINE-1 Retrotransposon Increases the Risk of Epithelial-Mesenchymal Transition and Metastasis in Epithelial Cancer.

Epithelial cancers comprise 80-90% of human cancers. During the process of cancer progression, cells lose their epithelial characteristics and acquire stem-like mesenchymal features that are resistant to chemotherapy. This process, termed the epithelial-mesenchymal transition (EMT), plays a critical role in the development of metastases. Because of the unique migratory and invasive properties of cells undergoing the EMT, therapeutic control of the EMT offers great hope and new opportunities for treating cancer. In recent years, a plethora of genes and noncoding RNAs, including miRNAs, have been linked to the EMT and the acquisition of stem cell-like properties. Despite these advances, questions remain unanswered about the molecular processes underlying such a cellular transition. In this article, we discuss how expression of the normally repressed LINE-1 (or L1) retrotransposons activates the process of EMT and the development of metastases. L1 is rarely expressed in differentiated stem cells or adult somatic tissues. However, its expression is widespread in almost all epithelial cancers and in stem cells in their undifferentiated state, suggesting a link between L1 activity and the proliferative and metastatic behaviour of cancer cells. We present an overview of L1 activity in cancer cells including how genes involved in proliferation, invasive and metastasis are modulated by L1 expression. The role of L1 in the differential expression of the let-7 family of miRNAs (that regulate genes involved in the EMT and metastasis) is also discussed. We also summarize recent novel insights into the role of the L1-encoded reverse transcriptase enzyme in epithelial cell plasticity that suggest it might be a potential therapeutic target that could reverse the EMT and the metastasis-associated stem cell-like properties of cancer cells.

The impact of glutathione transferase kappa deficiency on adiponectin multimerisation in vivo.

Glutathione transferase Kappa (GSTK1-1) also termed disulfide bond-forming oxidoreductase A-like protein (DsbA-L) has been implicated in the post-translational multimerization of adiponectin and has been negatively correlated with obesity in mice and humans. We investigated adiponectin in Gstk1(-/-) mice and surprisingly found no difference in the levels of total serum adiponectin or the level of high molecular weight (HMW) multimers when compared with normal controls. Non-reducing SDS-polyacrylamide gel electrophoresis and western blotting also showed a similar distribution of low, middle and HMW multimers in normal and Gstk1(-/-) mice. Variation in adiponectin has been correlated with glucose tolerance and with the levels of phosphorylated AMP-kinase but we found similar glucose tolerance and similar levels of phospho 5-AMP-activated protein kinase in normal and Gstk1(-/-) mice. Consequently, our findings suggest that GSTK1-1 is not absolutely required for adiponectin multimerization in vivo and alternate pathways may be activated in GSTK1-1 deficiency.

Interactions between dihydropyridine receptors and ryanodine receptors in striated muscle.

Excitation-contraction coupling in both skeletal and cardiac muscle depends on structural and functional interactions between the voltage-sensing dihydropyridine receptor L-type Ca(2+) channels in the surface/transverse tubular membrane and ryanodine receptor Ca(2+) release channels in the sarcoplasmic reticulum membrane. The channels are targeted to either side of a narrow junctional gap that separates the external and internal membrane systems and are arranged so that bi-directional structural and functional coupling can occur between the proteins. There is strong evidence for a physical interaction between the two types of channel protein in skeletal muscle. This evidence is derived from studies of excitation-contraction coupling in intact myocytes and from experiments in isolated systems where fragments of the dihydropyridine receptor can bind to the ryanodine receptors in sarcoplasmic reticulum vesicles or in lipid bilayers and alter channel activity. Although micro-regions that participate in the functional interactions have been identified in each protein, the role of these regions and the molecular nature of the protein-protein interaction remain unknown. The trigger for Ca(2+) release through ryanodine receptors in cardiac muscle is a Ca(2+) influx through the L-type Ca(2+) channel. The Ca(2+) entering through the surface membrane Ca(2+) channels flows directly onto underlying ryanodine receptors and activates the channels. This was thought to be a relatively simple system compared with that in skeletal muscle. However, complexities are emerging and evidence has now been obtained for a bi-directional physical coupling between the proteins in cardiac as well as skeletal muscle. The molecular nature of this coupling remains to be elucidated.

Identification and characterization of polymorphisms at the HAS alpha1-acid glycoprotein (ORM*) gene locus in Caucasians

Human alpha(1)-acid glycoprotein (AGP) or orosomucoid (ORM) is a major acute phase protein that is thought to play a crucial role in maintaining homeostasis. Human AGP is the product of a cluster of at least two adjacent genes located on HSA chromosome 9. Using a range of restriction endonucleases we have investigated DNA variation at the locus encoding the AGP genes in a group of healthy Caucasians. Polymorphisms were identified using BamHI, EcoRI, BglII, PvuII, HindIII, TaqI and MspI. Nonrandom associations were found between the BamHI, EcoRI and BglII RFLPs. The RFLPs detected with PvuII, TaqI and MspI were all located in exon 6 of both AGP genes. The duplication of an AGP gene was observed in 11 of the individuals studied and was in linkage disequilibrium with the TaqI RFLP. The identification and characterization of these polymorphisms should prove useful for other population and forensic studies

GSTZ1d: a new allele of glutathione transferase zeta and maleylacetoacetate isomerase.

The zeta class glutathione transferases (GSTs) are known to catalyse the isomerization of maleylacetoacetate (MAA) to fumarylacetoacetate (FAA), and the biotransformation of dichloroacetic acid to glyoxylate. A new allele of human GSTZ1, characterized by a Thr82Met substitution and termed GSTZ1d, has been identified by analysis of the expressed sequence tag (EST) database. In European Australians, GSTZ1d occurs with a frequency of 0.16. Like GSTZ1b-1b and GSTZ1c-1c, the new isoform has low activity with dichloroacetic acid compared with GSTZ1a-1a. The low activity appears to be due to a high sensitivity to substrate inhibition. The maleylacetoacetate isomerase (MAAI) activity of all known variants was compared using maleylacetone as a substrate. Significant differences in activity were noted, with GSTZ1a-1a having a notably lower catalytic efficiency. The unusual catalytic properties of GSTZ1a-1a in both reactions suggest that its characteristic arginine at position 42 plays a significant role in the regulation of substrate access and/or product release. The different amino acid substitutions have been mapped on to the recently determined crystal structure of GSTZ1-1 to evaluate and explain their influence on function.

Human monomethylarsonic acid (MMA(V)) reductase is a member of the glutathione-S-transferase superfamily.

The drinking of water containing large amounts of inorganic arsenic is a worldwide major public health problem because of arsenic carcinogenicity. Yet an understanding of the specific mechanism(s) of inorganic arsenic toxicity has been elusive. We have now partially purified the rate-limiting enzyme of inorganic arsenic metabolism, human liver MMA(V) reductase, using ion exchange, molecular exclusion, and hydroxyapatite chromatography. When SDS-beta-mercaptoethanol-PAGE was performed on the most purified fraction, seven protein bands were obtained. Each band was excised from the gel, sequenced by LC-MS/MS and identified according to the SWISS-PROT and TrEMBL Protein Sequence databases. Human liver MMA(V) reductase is 100% identical, over 92% of sequence that we analyzed, with the recently discovered human glutathione-S-transferase Omega class hGSTO 1-1. Recombinant human GSTO1-1 had MMA(V) reductase activity with K(m) and V(max) values comparable to those of human liver MMA(V) reductase. The partially purified human liver MMA(V) reductase had glutathione S-transferase (GST) activity. MMA(V) reductase activity was competitively inhibited by the GST substrate, 1-chloro 2,4-dinitrobenzene and also by the GST inhibitor, deoxycholate. Western blot analysis of the most purified human liver MMA(V) reductase showed one band when probed with hGSTO1-1 antiserum. We propose that MMA(V) reductase and hGSTO 1-1 are identical proteins.

Immunohistochemistry of omega class glutathione S-transferase in human tissues.

Omega class glutathione transferase (GSTO) has been recently described in a number of mammalian species. We used immunohistochemistry to determine the cellular and tissue distribution of GSTO1-1 in humans. Expression of GSTO1-1 was abundant in a wide range of normal tissues, particularly liver, macrophages, glial cells, and endocrine cells. We also found nuclear staining in several types of cells, including glial cells, myoepithelial cells of the breast, neuroendocrine cells of colon, fetal myocytes, hepatocytes, biliary epithelium, ductal epithelium of the pancreas, Hoffbauer cells of the placenta, and follicular and C-cells of the thyroid. These observations and the known activity of GSTO1-1 suggest biological functions that are not shared with other GSTs.

Dichloromethane mediated in vivo selection and functional characterization of rat glutathione S-transferase theta 1-1 variants.

Methylobacterium dichloromethanicum DM4 is able to grow with dichloromethane as the sole carbon and energy source by using a dichloromethane dehalogenase/glutathione S-transferase (GST) for the conversion of dichloromethane to formaldehyde. Mammalian homologs of this bacterial enzyme are also known to catalyze this reaction. However, the dehalogenation of dichloromethane by GST T1-1 from rat was highly mutagenic and toxic to methylotrophic bacteria. Plasmid-driven expression of rat GST T1-1 in strain DM4-2cr, a mutant of strain DM4 lacking dichloromethane dehalogenase, reduced cell viability 10(5)-fold in the presence of dichloromethane. This effect was exploited to select dichloromethane-resistant transconjugants of strain DM4-2cr carrying a plasmid-encoded rGSTT1 gene. Transconjugants that still expressed the GST T1 protein after dichloromethane treatment included rGSTT1 mutants encoding protein variants with sequence changes from the wild-type ranging from single residue exchanges to large insertions and deletions. A structural model of rat GST T1-1 suggested that sequence variation was clustered around the glutathione activation site and at the protein C-terminus believed to cap the active site. The enzymatic activity of purified His-tagged GST T1-1 variants expressed in Escherichia coli was markedly reduced with both dichloromethane and the alternative substrate 1,2-epoxy-3-(4'-nitrophenoxy)propane. These results provide the first experimental evidence for the involvement of Gln102 and Arg107 in catalysis, and illustrate the potential of in vivo approaches to identify catalytic residues in GSTs whose activity leads to toxic effects.

Crystal structure of maleylacetoacetate isomerase/glutathione transferase zeta reveals the molecular basis for its remarkable catalytic promiscuity.

Maleylacetoacetate isomerase (MAAI), a key enzyme in the metabolic degradation of phenylalanine and tyrosine, catalyzes the glutathione-dependent isomerization of maleylacetoacetate to fumarylacetoacetate. Deficiencies in enzymes along the degradation pathway lead to serious diseases including phenylketonuria, alkaptonuria, and the fatal disease, hereditary tyrosinemia type I. The structure of MAAI might prove useful in the design of inhibitors that could be used in the clinical management of the latter disease. Here we report the crystal structure of human MAAI at 1.9 A resolution in complex with glutathione and a sulfate ion which mimics substrate binding. The enzyme has previously been shown to belong to the zeta class of the glutathione S-transferase (GST) superfamily based on limited sequence similarity. The structure of MAAI shows that it does adopt the GST canonical fold but with a number of functionally important differences. The structure provides insights into the molecular bases of the remarkable array of different reactions the enzyme is capable of performing including isomerization, oxygenation, dehalogenation, peroxidation, and transferase activity.

Identification of the apical membrane-targeting signal of the multidrug resistance-associated protein 2 (MRP2/MOAT).

The human canalicular multispecific organic anion transporter (cMOAT), known as the multidrug resistance-associated protein 2 (MRP2), is normally expressed in the liver and to a lesser extent in the kidney proximal tubules. In these tissues MRP2 specifically localizes to the apical membrane. The construction of MRP2 fused to the green fluorescent protein, and subsequent site-directed mutagenesis enabled the identification of a targeting signal in MRP2 that is responsible for its apical localization in polarized cells. The specific apical localization of MRP2 is due to a C-terminal tail that is not present in the basolaterally targeted MRP1. Deletion of three amino acids from the C-terminal of MRP2 (DeltaMRP2) causes the protein to be localized predominantly in the basolateral membrane in polarized Madin-Darby canine kidney cells. Interestingly, MRP2 expressed in a mouse leukemia cell line (L1210 cells) predominantly accumulates intracellularly with minimal cell membrane localization. In contrast, DeltaMRP2 was shown to predominantly localize in the cell membrane in L1210 cells. Increased transport of 2,4-dinitrophenyl glutathione from L1210 cells expressing DeltaMRP2 showed that the re-targeted protein retains its normal function.

Identification of novel glutathione transferases and polymorphic variants by expressed sequence tag database analysis.

The human expressed sequence tag (EST) database can be searched by different sequence alignment strategies to identify new members of gene families and allelic variants. To illustrate the value of database analysis for gene discovery, we have focused on the glutathione S-transferase (GST) super family, an approach that has led to the identification of the Zeta class. The Zeta class GSTs catalyze the glutathione-dependent biotransformation of alpha-haloacids and the isomerization of maleylacetoacetic acid to fumarylacetoacetic acid, an essential step in the catabolism of tyrosine. Allelic variants of the GST Z1 and GST A2 genes have also been identified by EST database analysis. One GST Z1 variant (GST Z1A) has significantly higher activity with dichloroacetic acid as a substrate than other GST Z1 isoforms. This variant may be important in the clinical treatment of lactic acidosis where dichloroacetic acid is prescribed. Our experience with the application of EST database searching methods suggests that it may be productively applied to other gene families of pharmacogenetic interest.

Human glutathione transferase T2-2 discloses some evolutionary strategies for optimization of substrate binding to the active site of glutathione transferases.

Rapid kinetic, spectroscopic, and potentiometric studies have been performed on human Theta class glutathione transferase T2-2 to dissect the mechanism of interaction of this enzyme with its natural substrate GSH. Theta class glutathione transferases are considered to be older than Alpha, Pi, and Mu classes in the evolutionary pathway. As in the more recently evolved GSTs, the activation of GSH in the human Theta enzyme proceeds by a forced deprotonation of the sulfhydryl group (pK(a) = 6.1). The thiol proton is released quantitatively in solution, but above pH 6.5, a protein residue acts as an internal base. Unlike Alpha, Mu, and Pi class isoenzymes, the GSH-binding mechanism occurs via a simple bimolecular reaction with k(on) and k(off) values at least hundred times lower (k(on) = (2.7 +/- 0.8) x 10(4) M(-1) s(-1), k(off) = 36 +/- 9 s(-1), at 37 degrees C). Replacement of Arg-107 by alanine, using site-directed mutagenesis, remarkably increases the pK(a) value of the bound GSH and modifies the substrate binding modality. Y107A mutant enzyme displays a mechanism and rate constants for GSH binding approaching those of Alpha, Mu, and Pi isoenzymes. Comparison of available crystallographic data for all these GSTs reveals an unexpected evolutionary trend in terms of flexibility, which provides a basis for understanding our experimental results.

Human glutathione transferase T2-2 discloses some evolutionary strategies for optimization of the catalytic activity of glutathione transferases.

Steady state, pre-steady state kinetic experiments, and site-directed mutagenesis have been used to dissect the catalytic mechanism of human glutathione transferase T2-2 with 1-menaphthyl sulfate as co-substrate. This enzyme is close to the ancestral precursor of the more recently evolved glutathione transferases belonging to Alpha, Pi, and Mu classes. The enzyme displays a random kinetic mechanism with very low k(cat) and k(cat)/K(m)((GSH)) values and with a rate-limiting step identified as the product release. The chemical step, which is fast and causes product accumulation before the steady state catalysis, strictly depends on the deprotonation of the bound GSH. Replacement of Arg-107 with Ala dramatically affects the fast phase, indicating that this residue is crucial both in the activation and orientation of GSH in the ternary complex. All pre-steady state and steady state kinetic data were convincingly fit to a kinetic mechanism that reflects a quite primordial catalytic efficiency of this enzyme. It involves two slowly interconverting or not interconverting enzyme populations (or active sites of the dimeric enzyme) both able to bind and activate GSH and strongly inhibited by the product. Only one population or subunit is catalytically competent. The proposed mechanism accounts for the apparent half-site behavior of this enzyme and for the apparent negative cooperativity observed under steady state conditions. These findings also suggest some evolutionary strategies in the glutathione transferase family that have been adopted for the optimization of the catalytic activity, which are mainly based on an increased flexibility of critical protein segments and on an optimal orientation of the substrate.