A reporter gene construct for studying the regulation of manganese peroxidase gene expression

Peroxisome proliferator-activated receptor γ inhibits pulmonary hypertension targeting store-operated calcium entry

In this study, we investigated the role of peroxisome proliferator-activated receptor γ (PPARγ) on store-operated calcium entry (SOCE) and expression of the main store-operated calcium channel (SOCCs) components, canonical transient receptor potential (TRPC) in chronic hypoxia (CH)-induced pulmonary hypertension (CHPH) rat models. Small interfering RNA (siRNA) knockdown and adenoviral overexpression strategies were constructed for loss-of-function and gain-of-function experiments. PPARγ agonist rosiglitazone attenuates the pathogenesis of CHPH and suppresses Hif-1α, TRPC1, TRPC6 expression in the distal pulmonary arteries (PA), and SOCE in freshly isolated rat distal pulmonary arterial smooth muscle cells (PASMCs). By comprehensive use of knockdown and overexpression studies, and bioinformatical analysis of the TRPC gene promoter and luciferase reporter assay, we demonstrated that PPARγ exerts roles of anti-proliferation, anti-migration, and pro-apoptosis in PASMCs, likely by inhibiting the elevated SOCE and TRPC expression. These effects were inhibited under the conditions of hypoxia or Hif-1α accumulation. We also found that under hypoxia, accumulated Hif-1α protein acts as upstream of suppressed PPARγ level; however, targeted PPARγ rescue acts as negative feedback on suppressing Hif-1α level and Hif-1α mediated signaling pathway. PPARγ inhibits CHPH by targeting SOCE and TRPC via inhibiting Hif-1α expression and signaling transduction.

KEY MESSAGES

Rosiglitazone protects PH by normalizing RVSP but not right ventricle hypotrophy. PPARγ inhibits PASMCs proliferation via targeting SOCE and TRPC by suppressing Hif-1α. PPARγ and Hif-1α share mutual inhibitory regulation in PASMCs. PPARγ restoration might be a beneficial strategy for PH treatment.

Ligninolytic peroxidase gene expression by Pleurotus ostreatus: differential regulation in lignocellulose medium and effect of temperature and pH

Pleurotus ostreatus is an important edible mushroom and a model lignin degrading organism, whose genome contains nine genes of ligninolytic peroxidases, characteristic of white-rot fungi. These genes encode six manganese peroxidase (MnP) and three versatile peroxidase (VP) isoenzymes. Using liquid chromatography coupled to tandem mass spectrometry, secretion of four of these peroxidase isoenzymes (VP1, VP2, MnP2 and MnP6) was confirmed when P. ostreatus grows in a lignocellulose medium at 25°C (three more isoenzymes were identified by only one unique peptide). Then, the effect of environmental parameters on the expression of the above nine genes was studied by reverse transcription-quantitative PCR by changing the incubation temperature and medium pH of P. ostreatus cultures pre-grown under the above conditions (using specific primers and two reference genes for result normalization). The cultures maintained at 25°C (without pH adjustment) provided the highest levels of peroxidase transcripts and the highest total activity on Mn(2+) (a substrate of both MnP and VP) and Reactive Black 5 (a VP specific substrate). The global analysis of the expression patterns divides peroxidase genes into three main groups according to the level of expression at optimal conditions (vp1/mnp3>vp2/vp3/mnp1/mnp2/mnp6>mnp4/mnp5). Decreasing or increasing the incubation temperature (to 10°C or 37°C) and adjusting the culture pH to acidic or alkaline conditions (pH 3 and 8) generally led to downregulation of most of the peroxidase genes (and decrease of the enzymatic activity), as shown when the transcription levels were referred to those found in the cultures maintained at the initial conditions. Temperature modification produced less dramatic effects than pH modification, with most genes being downregulated during the whole 10°C treatment, while many of them were alternatively upregulated (often 6h after the thermal shock) and downregulated (12h) at 37°C. Interestingly, mnp4 and mnp5 were the only peroxidase genes upregulated under alkaline pH conditions. The differences in the transcription levels of the peroxidase genes when the culture temperature and pH parameters were changed suggest an adaptive expression according to environmental conditions. Finally, the intracellular proteome was analyzed, under the same conditions used in the secretomic analysis, and the protein product of the highly-transcribed gene mnp3 was detected. Therefore, it was concluded that the absence of MnP3 from the secretome of the P. ostreatus lignocellulose cultures was related to impaired secretion.

Novel promoter sequence required for manganese regulation of manganese peroxidase isozyme 1 gene expression in Phanerochaete chrysosporium

Manganese peroxidase (MnP) is a major, extracellular component of the lignin-degrading system produced by the wood-rotting basidiomycetous fungus Phanerochaete chrysosporium. The transcription of MnP-encoding genes (mnps) in P. chrysosporium occurs as a secondary metabolic event, triggered by nutrient-nitrogen limitation. In addition, mnp expression occurs only under Mn2+ supplementation. Using a reporter system based on the enhanced green fluorescent protein gene (egfp), we have characterized the P. chrysosporium mnp1 promoter by examining the effects of deletion, replacement, and translocation mutations on mnp1 promoter-directed egfp expression. The 1,528-bp mnp1 promoter fragment drives egfp expression only under Mn2+-sufficient, nitrogen-limiting conditions, as required for endogenous MnP production. However, deletion of a 48-bp fragment, residing 521 bp upstream of the translation start codon in the mnp1 promoter, or replacement of this fragment with an unrelated sequence resulted in egfp expression under nitrogen limitation, both in the absence and presence of exogenous Mn2+. Translocation of the 48-bp fragment to a site 120 bp downstream of its original location resulted in Mn2+-dependent egfp expression under conditions similar to those observed with the wild-type mnp1 promoter. These results suggest that the 48-bp fragment contains at least one Mn2+-responsive cis element. Additional promoter-deletion experiments suggested that the Mn2+ element(s) is located within the 33-bp sequence at the 3' end of the 48-bp fragment. This is the first promoter sequence containing a Mn2+-responsive element(s) to be characterized in any eukaryotic organism.

Homologous expression of Phanerochaete chrysosporium manganese peroxidase, using bialaphos resistance as a dominant selectable marker

Manganese peroxidase (MnP) is a major extracellular component of the lignin-degrading system of the white-rot fungus, Phanerochaete chrysosporium. Homologous expression of recombinant MnP isozyme 1 (rMnP1) in P. chrysosporium was achieved using a novel transformation system for this fungus, which utilizes the Streptomyces hygroscopicus bialaphos-resistant gene, bar, as the selectable marker. The transformation frequency for this system is approximately 100 bialaphos-resistant transformants per microgram of plasmid DNA. Transformed strains all contain plasmid DNA, ectopically integrated into the fungal genome. Using this transformation system, the promoter region of the P. chrysosporium translation elongation factor gene was used to drive expression of mnp1, encoding MnP1, in primary metabolic cultures of P. chrysosporium, where endogenous MnP was not expressed. Approximately 2-3 mg of active recombinant MnP1 per liter of extracellular medium was produced in agitated cultures of transformants.

The green fluorescent protein gene functions as a reporter of gene expression in Phanerochaete chrysosporium

The enhanced green fluorescent protein (GFP) gene (egfp) was used as a reporter of gene expression driven by the glyceraldehyde-p-dehydrogenase (gpd) gene promoter and the manganese peroxidase isozyme 1 (mnp1) gene promoter in Phanerochaete chrysosporium. Four different constructs were prepared. pUGGM3' and pUGiGM3' contain the P. chrysosporium gpd promoter fused upstream of the egfp coding region, and pUMGM3' and pUMiGM3' contain the P. chrysosporium mnp1 promoter fused upstream of the egfp gene. In all constructs, the egfp gene was followed by the mnp1 gene 3' untranslated region. In pUGGM3' and pUMGM3', the promoters were fused directly with egfp, whereas in pUGiGM3' and pUMiGM3', following the promoters, the first exon (6 bp), the first intron (55 bp), and part of the second exon (9 bp) of the gpd gene were inserted at the 5' end of the egfp gene. All constructs were ligated into a plasmid containing the ura1 gene of Schizophyllum commune as a selectable marker and were used to transform a Ural1 auxotrophic strain of P. chrysosporium to prototrophy. Crude cell extracts were examined for GFP fluorescence, and where appropriate, the extracellular fluid was examined for MnP activity. The transformants containing a construct with an intron 5' of the egfp gene (pUGiGM3' and pUMiGM3') exhibited maximal fluorescence under the appropriate conditions. The transformants containing constructs with no introns exhibited minimal or no fluorescence. Northern (RNA) blots indicated that the insertion of a 5' intron resulted in more egfp RNA than was found in transformants carrying an intronless egfp. These results suggest that the presence of a 5' intron affects the expression of the egfp gene in P. chrysosporium. The expression of GFP in the transformants carrying pUMiGM3' paralled the expression of endogenous mnp with respect to nitrogen and Mn levels, suggesting that this construct will be useful in studying cis-acting elements in the mnp1 gene promoter.

Role of arginine 177 in the MnII binding site of manganese peroxidase. Studies with R177D, R177E, R177N, and R177Q mutants

Previously, we reported that Arg177 is involved in MnII binding at the MnII binding site of manganese peroxidase isozyme 1 (MnP1) of Phanerochaete chrysosporium by examining two mutants: R177A and R177K. We now report on additional mutants: R177D, R177E, R177N, and R177Q. These new mutant enzymes were produced by homologous expression in P. chrysosporium and were purified to homogeneity. The molecular mass and the UV/visible spectra of the ferric and oxidized intermediates of the mutant enzymes were similar to those of the wild-type enzyme, suggesting proper folding, heme insertion, and preservation of the heme environment. However, steady-state and transient-state kinetic analyses demonstrate significantly altered characteristics of MnII oxidation by these new mutant enzymes. Increased dissociation constants (Kd) and apparent Km values for MnII suggest that these mutations at Arg177 decrease binding of MnII to the enzyme. These lowered binding efficiencies, as observed with the R177A and R177K mutants, suggest that the salt-bridge between Arg177 and the MnII binding ligand Glu35 is disrupted in these new mutants. Decreased kcat values for MnII oxidation, decreased second-order rate constants for compound I reduction (k2app), and decreased first-order rate constants for compound II reduction (k3) indicate that these new mutations also decrease the electron-transfer rate. This decrease in rate constants for compounds I and II reduction was not observed in our previous study on the R177A and R177K mutations. The lower rate constants suggest that, even with high MnII concentrations, the MnII binding geometries may be altered in the MnII binding site of these new mutants. These new results, combined with the results from our previous study, clearly indicate a role for Arg177 in promoting efficient MnII binding and oxidation by MnP.

Fungi in lignocellulose breakdown and biopulping

Biological pulping has the potential to improve the quality of pulp, properties of paper and to reduce energy costs and environmental impact relative to traditional pulping operations. It has been suggested that energy savings alone could make the process economically viable. Other benefits include improved burst strength and tear indices of the product and reduced pitch deposition during the production process. The technology has focused on the white rot fungi, which have complex extracellular ligninolytic enzyme systems that can selectively remove or alter lignin and allow cellulose fibers to be obtained. Although still far from completely understood, these enzyme systems are being characterized mechanistically and on a molecular level with primary emphasis on the enzymes lignin peroxidase, manganese peroxidase and laccase. Scale-up to industrial process requirements presents challenges that are difficult to simulate in laboratory or pilot-scale tests. Inoculation, aeration and heat dissipation are key parameters for maintaining fungal activity. It may be possible to monitor and maintain consistent treatments through a program of active wood chip pile management. Overcoming these challenges will determine, in large part, if biopulping becomes a reality.

The yeast Cryptococcus neoformans uses 'mammalian' enhancer sites in the regulation of the virulence gene, CNLAC1

Transcriptional regulation in mammalian and plant cells is distinguished from fungi by the presence of blocks of multiple interacting DNA binding sites distributed over a relatively large upstream region of genes and the ability to use glutamine-rich enhancers such as Sp1. We offer evidence that the haploid yeast Cryptococcus neoformans contains a virulence gene, CNLAC1, having regulatory properties more similar to mammalian systems than to that of yeast. We used a novel promoter plasmid, pVEW, and electromobility shift assay techniques adapted for the fungus for the first systematic structural and functional study of a 5'-enhancer region of a basidiomycete fungus using the upstream region of CNLAC1. Two groups of interactive enhancer regions, located over a range of 1.5kb from the mRNA start site are involved in CNLAC1 regulation (region 2: -1721 to -1615 and region 7) in addition to a TATA promoter at position -539. Region 2 contains a consensus Sp1 site and region 7 contains a consensus E2F site, each of which shows significant binding to nuclear proteins under derepressed conditions; cooperative binding was also suggested between DNA-binding protein of these sites and those binding nearby CCAAT sequences in each region. Two regions of repression were also evident under derepressed conditions (region 5: -1351 to -1207 and region 8: -991 to -971). Identification of functional Sp1 binding sites and the presence of multiple interactive enhancer sites over a fairly large upstream range suggests that cryptococcal transcriptional regulation contains features often associated with higher eukaryotic regulation. C. neoformans thus may provide a unique system for the study of certain aspects of higher eukaryotic transcription, using yeast genetic approaches. In addition, properties of basidiomycete yeast such as Cryptococcus exemplified in the present study suggest an evolutionary progression in gene regulation within fungi toward properties exhibited in the kingdoms Animalia and Plantae.

Reverse transcription-PCR analysis of the regulation of the manganese peroxidase gene family

Manganese peroxidase (MnP) gene expression in the lignin-degrading fungus Phanerochaete chrysosporium is regulated by nutrient nitrogen levels and by Mn(II), the substrate for the enzyme, as well as by heat shock and other factors. Reverse transcription-PCR (RT-PCR) of total RNA can distinguish the mRNAs of each of the three sequenced P. chrysosporium mnp genes, i.e., mnp1, mnp2, and mnp3. Quantitative RT-PCR demonstrates that each of the three transcripts is present at a similar low basal level in nitrogen-sufficient cultures, with or without Mn, and in nitrogen-limited cultures lacking Mn. However, in 5-day-old, nitrogen-limited, stationary cultures supplemented with 180 microM Mn, the levels of the mnp1 and mnp2 transcripts increased approximately 100- and 1,700-fold, respectively, over basal levels. In contrast, under these conditions, the level of the mnp3 transcript did not increase significantly over the basal level. Quantitative RT-PCR of total RNA extracted from nitrogen-deficient, Mn-supplemented cultures on days 2 through 7 demonstrates that whereas the mnp1 transcript was present at relatively low levels on days 3 through 7, the mnp2 transcript level peaked on day 5 and the mnp3 transcript level peaked on day 3. Comparison of total RNA extracted on day 5 from nitrogen-deficient, Mn-supplemented stationary and agitated cultures indicates that in stationary cultures, mnp2 was the major expressed mnp gene, whereas in large agitated cultures, mnp1 was the major expressed mnp gene.

Purification and characterization of two manganese peroxidase isozymes from the white-rot basidiomycete Dichomitus squalens

Two manganese peroxidase isozymes, MnP1 and MnP2, were purified from the extracellular medium of ligninolytic cultures of Dichomitus squalens. The proteins were purified to homogeneity using DEAE-Sepharose chromatography and Mono Q fast protein liquid chromatography. MnP1 and MnP2 have molecular masses of 48000 and 48900 Da, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both isozymes are glycoproteins and each contains one iron protoporphyrin IX as a prosthetic group. The pl values of MnP1 and MnP2 are 4.15 and 3.90, respectively. N-Terminal amino-acid analysis suggests that these proteins are encoded by distinct genes. The Soret bands of the native ferric enzymes (408 nm and 406 nm, respectively) are shifted to 434 nm in the reduced enzymes and to 422 nm in the reduced-CO complexes. EPR g-values of the native enzymes are essentially identical to those for other MnPs and lignin peroxidases, and they confirm the high-spin state of the iron. The addition of 1 equivalent of H2O2 to either of the native ferric isozymes yields spectra which are characteristic of compound 1. Successive additions of 1 equivalent of ferrocyanide and 1 equivalent of H2O2 to the native enzymes yield spectra which are characteristic of compound II. Both MnP isozymes oxidize Mn2+ to Mn3+ in the presence of organic acid chelators. The MnP isozymes are produced by D. squalens only when the cells are grown in the presence of Mn.

Regulation of manganese peroxidase gene transcription by hydrogen peroxide, chemical stress, and molecular oxygen

The expression of manganese peroxidase (MnP) in nitrogen-limited cultures of the lignin-degrading fungus Phanerochaete chrysosporium is regulated at the level of gene transcription by H2O2 and various chemicals, including ethanol, sodium arsenite, and 2,4-dichlorophenol, as well as by Mn(II) and heat shock. Northern (RNA) blot analysis demonstrates that the addition of 1.0 mM H2O2 to 5-day-old cultures grown in the absence of Mn results in the appearance of mnp mRNA within 15 min. Higher levels of mnp mRNA are obtained with simultaneous induction by Mn and H2O2 than with H2O2 alone. Although neither MnP activity nor associated protein is detectable in H2O2-induced cultures grown in the absence of Mn, simultaneous induction with Mn and H2O2 results in a 1.6-fold increase in MnP activity compared with the MnP activity resulting from Mn induction alone. In the presence of Mn, purging of low-nitrogen cultures with 100% O2, in contrast to incubation under air, results in an increase in the accumulation of mnp mRNA and a 13-fold increase in MnP activity on day 5. However, in contrast to the effects of H2O2 and heat shock, O2 purging of Mn-deficient cultures results in negligible accumulation of mnp mRNA.

Homologous expression of recombinant manganese peroxidase in Phanerochaete chrysosporium

The promoter region of the glyceraldehyde-3-phosphate dehydrogenase gene (gpd) was used to drive expression of mnp1, the gene encoding Mn peroxidase isozyme 1, in primary metabolic cultures of Phanerochaete chrysosporium. A 1,100-bp fragment of the P. chrysosporium gpd promoter region was fused upstream of the mnp1 gene to construct plasmid pAGM1, which contained the Schizophyllum commune ade5 gene as a selectable marker. pAGM1 was used to transform a P. chrysosporium ade1 auxotroph to prototrophy. Ade+ transformants were screened for peroxidase activity on a solid medium containing high carbon and high nitrogen (2% glucose and 24 mM NH4 tartrate) and o-anisidine as the peroxidase substrate. Several transformants that expressed high peroxidase activities were purified and analyzed further in liquid cultures. Recombinant Mn peroxidase (rMnP) was expressed and secreted by transformant cultures on day 2 under primary metabolic growth conditions (high carbon and high nitrogen), whereas endogenous wild-type mnp genes were not expressed under these conditions. Expression of rMnP was not influenced by the level of Mn in the culture medium, as previously observed for the wild-type Mn peroxidase (wtMnP). The amount of active rMnP expressed and secreted in this system was comparable to the amount of enzyme expressed by the wild-type strain under ligninolytic conditions. rMnP was purified to homogeneity by using DEAE-Sepharose chromatography, Blue Agarose chromatography, and Mono Q column chromatography. The M(r) and absorption spectrum of rMnP were essentially identical to the M(r) and absorption spectrum of wtMnP, indicating that heme insertion, folding, and secretion were normal.(ABSTRACT TRUNCATED AT 250 WORDS)