An AP1 element is involved in transcriptional regulation of delta9-desaturase gene of Histoplasma capsulatum

Polymorphism in the flanking regions of the PbGP43 gene from the human pathogen Paracoccidioides brasiliensis: search for protein binding sequences and poly(A) cleavage sites

Background

Paracoccidioides brasiliensis is a thermo-dimorphic fungus that causes paracoccidiodomycosis (PCM). Glycoprotein gp43 is the fungal main diagnostic antigen, which can also protect against murine PCM and interact with extracellular matrix proteins. It is structurally related to glucanases, however not active, and whose expression varies considerably. We have presently studied polymorphisms in the PbGP43 flanking regions to help understand such variations.

Results

we tested the protein-binding capacity of oligonucleotides covering the PbGP43 proximal 5' flanking region, including overlap and mutated probes. We used electrophoretic mobility shift assays and found DNA binding regions between positions -134 to -103 and -255 to -215. Only mutation at -230, characteristic of P. brasiliensis phylogenetic species PS2, altered binding affinity. Next, we cloned and sequenced the 5' intergenic region up to position -2,047 from P. brasiliensis Pb339 and observed that it is composed of three tandem repetitive regions of about 500 bp preceded upstream by 442 bp. Correspondent PCR fragments of about 2,000 bp were found in eight out of fourteen isolates; in PS2 samples they were 1,500-bp long due to the absence of one repetitive region, as detected in Pb3. We also compared fifty-six PbGP43 3' UTR sequences from ten isolates and have not observed polymorphisms; however we detected two main poly(A) clusters (1,420 to 1,441 and 1,451 to 1,457) of multiple cleavage sites. In a single isolate we found one to seven sites.

Conclusions

We observed that the amount of PbGP43 transcripts accumulated in P. brasiliensis Pb339 grown in defined medium was about 1,000-fold higher than in Pb18 and 120-fold higher than in Pb3. We have described a series of features in the gene flanking regions and differences among isolates, including DNA-binding sequences, which might impact gene regulation. Little is known about regulatory sequences in thermo-dimorphic fungi. The peculiar structure of tandem repetitive fragments in the 5' intergenic region of PbGP43, their characteristic sequences, besides the presence of multiple poly(A) cleavage sites in the 3' UTR will certainly guide future studies.

Neutral storage lipids of Histoplasma capsulatum: effect of culture age

Lipids contribute significantly to the pathogenesis of fungal infectious diseases and an understanding of lipid metabolism occurring in fungal pathogens can help the development of more efficient antifungal therapeutic strategies. In this study, the effect of culture age on the distribution of fatty acids among different neutral lipid (NL) classes in the dimorphic fungus Histoplasma capsulatum was investigated. Yeast cells of the G217B strain grown in two different media were collected after 4 and 7 days of growth, which roughly correspond to log and stationary culture growth phases, respectively. Neither culture age nor medium type had any influence on qualitative fatty acid (FA) profiles; however, the FA percentage composition varied with culture growth. A culture age-related decrease in the content of unsaturated FAs could be observed in all four of the NL classes examined, but the most intensive changes were detected in diacylglycerol and free FA fractions. Conversely, an increase in saturated FAs was observed. The transcriptional analysis of two major delta 9- and delta 12-FA desaturase genes, ode1 and sde1, showed no differences in their expression levels under experimental conditions. These results showing the dynamics of changes in FA composition in the NL fraction were concomitant with nutrient exhaustion in aging H. capsulatum cultures. Overall, the results presented in this work not only have implications for our knowledge of basic lipid biochemistry of H. capsulatum, but also will contribute to better understanding of biology and pathogenesis of this fungus and, consequently, can help in the discovery of more effective antifungal drugs.

Identification of a novel delta9-fatty acid desaturase gene and its promoter from oil-producing fungus Rhizopus arrhizus

Reverse Transcriptional Polymerase Chain Reaction (RT-PCR), Rapid Amplification of the cDNA ends (RACE) and Thermal asymmetric interlaced (TAIL)-PCR were used successfully to clone the open reading frame (1,377 bp) of delta9-fatty acid desaturase gene (named as RAD9) and its promoter region from oil-producing fungi Rhizopus arrhizus. Functional identification of the protein was done by sub-cloning RAD9 into the expression vector pYES2.0 to generate a recombinant plasmid pYRAD9, which was then subsequently transformed into Saccharomyces cerevisiae delta9-fatty acid desaturase mutation strain L8-14C to be expressed under the control of GAL1 promoter. The transformant containing RAD9 named as L8-14C-pYRAD9 could grow on the synthetic minimal medium plate with out oleic acid supplement. Fatty acid analysis also showed that the transformant contained 16:1 and 18:1. This indicated that pYRAD9 could successfully complement the mutation of L8-14C. Computational analysis of the nucleotide sequence of RAD9 promoter showed several basic transcriptional elements including a CAAT box, a GC box, a CACCC box, two TATA boxes and also several putative target-binding sites for transcription factors, which have been reported to be involved in the regulation of lipid metabolism. Preliminary functional analysis of this promoter in S. cerevisiae was done using lacZ report gene.

Identification of transcription elements in the 5′ intergenic region shared by LON and MDJ1 heat shock genes from the human pathogen Paracoccidioides brasiliensis. Evaluation of gene expression

The MDJ1/LON locus is conserved among pathogenic dimorphic fungi. We have mapped using DNase I footprinting and mobility shift assays three putative heat shock elements and one AP-1 binding domain (ARE) in the 5' intergenic region shared by PbMDJ1and PbLON (ML) from Paracoccidioides brasiliensis. The region bearing an ARE-like towards PbLON also has an opposite skn-1-like element. We studied genetically and pathogenically distinct isolates Pb18 and Pb3, where ML is polymorphic and the number of elements detected was higher. The functionality of the elements was suggested by the stimulatory response of both genes to heat shock and oxidative stress. Co-regulation occurred upon heat shock from 36 to 42 degrees C and, only in Pb3, also during mycelium to yeast transformation (26-36 degrees C). In Pb18, PbMDJ1 seemed to be preferentially expressed in yeast. Our study might help understand regulation of genes involved in fungal adaptation to the host.

Promoter analysis of Mucor rouxii delta9-desaturase: its implication for transcriptional regulation in Saccharomyces cerevisiae

Promoter study was performed to understand the transcriptional control of delta9-desaturase gene of Mucor rouxii. Several putative cis-elements involved in lipid metabolism were mapped by computational analysis. 5' deletion analysis shows the presence of elements with repressing activity, especially in 122 bp located upstream of the transcription start site. Truncation of these repressor domains showed that the promoter of M. rouxii is functional in Saccharomyces cerevisiae without additional components and is insensitive to nutritional depletion. The promoter also drove effectively the expression of a M. rouxii delta12-desaturase gene, and the linoleic acid content increased with the age of the yeast culture in parallel with the promoter activity. This approach provides a genetic tool for programming heterologous protein production in the yeast.

Cyp1a2 protects against reactive oxygen production in mouse liver microsomes

H(2)O(2) production was evaluated in liver microsomes prepared from Cyp1a1/1a2(+/+) wild-type and Cyp1a1(-/-) and Cyp1a2(-/-) knockout mice pretreated with 5 microg dioxin (TCDD)/kg body wt or vehicle alone. NADPH-dependent H(2)O(2) production in TCDD-induced microsomes from wild-type mice was about one-third of that in noninduced microsomes. In Cyp1a2(-/-) mice, H(2)O(2) production was the same for induced and noninduced microsomes, with levels significantly higher than those in wild-type mice. Cyp1a1(-/-) microsomes displayed markedly lower levels of H(2)O(2) production in both induced and noninduced microsomes, compared with those in wild-type and Cyp1a2(-/-) microsomes. The CYP1A2 inhibitor furafylline in vitro exacerbated microsomal H(2)O(2) production proportional to the degree of CYP1A2 inhibition, and the CYP2E1 inhibitor diethyldithiocarbamate decreased H(2)O(2) production proportional to the degree of CYP2E1 inhibition. Microsomal H(2)O(2) production was strongly correlated to NADPH-stimulated production of thiobarbituric acid-reactive substances, as well as to decreases in microsomal membrane polarization anisotropy, indicative of peroxidation of unsaturated membrane lipids. Our results suggest that possibly acting as an "electron sink," CYP1A2 might decrease CYP2E1-and CYP1A1-mediated H(2)O(2) production and oxidative stress. In this regard, CYP1A2 may be considered an antioxidant enzyme.

Changes in membrane fatty acids and delta-9 desaturase in senescence accelerated (SAMP8) mouse hippocampus with aging

Senescence accelerated mice (SAMP8) exhibit age induced impairments such as loss of memory and learning disabilities by the age of 8-10 months. Analysis of hippocampus of SAMP8 mice revealed that delta 9-desaturase (delta9desaturase) activity reduced up to 44-50% with age. Correspondingly, levels of unsaturated fatty acids are also lowered in the aged animals approximately to the same levels. RNase protection assay showed that delta9specific message decreased similarly with age. As such a decrease is known to cause alterations in membrane fluidity and affect cellular signaling pathways, these results suggest that lowering of delta9gene expression may be partly involved in age induced impairments.

CDR1, a multidrug resistance gene from Candida albicans, contains multiple regulatory domains in its promoter and the distal AP-1 element mediates its induction by miconazole

We previously demonstrated that the CDR1 gene, encoding a multidrug transporter in Candida albicans, is differentially upregulated by various drugs and steroids. In order to get an insight into the molecular basis of the induction of this gene we analyzed its promoter region. The transcription start site was mapped to 63 nucleotides upstream of the initiating ATG. Reporter assays revealed the presence of four upstream activating and four upstream repressing sequence domains along the entire promoter. Like the native gene, promoter-luciferase recombinants showed enhanced activity in response to various stresses like drugs, human steroid hormones and heavy metals. Mutational analysis demonstrated that while the proximal promoter (-345/+1) contains all the regulatory domains required for its induction by various other stresses, the miconazole response is mediated via the distal promoter (-857/-1147), harboring an AP-1 site. The involvement of the AP-1 element in mediating the latter effect was evident by an increase in AP-1 binding activity following miconazole treatment.

Characterization of a gene encoding a developmentally regulated winged helix transcription factor of the sea urchin Strongylocentrotus purpuratus

Spfkh1 is a Strongylocentrotus purpuratus transcription factor that contains a winged helix DNA binding domain. Both the gene and overlapping cDNAs encoding this factor have been cloned and completely sequenced. We have mapped the start of transcription by primer extension to a site 600 base pairs 5' to the start of translation. Spfkh1 is transcribed in one open reading frame that contains the DNA binding domain, nuclear localization signal and transactivation domain. The deduced amino acid sequence encodes a 40. 7kDa protein with a pI of 9.96. Alignments of the DNA binding domain with other forkhead domains reveal that this gene falls into Class II of the winged helix transcription factors. We have identified a unique carboxyl-terminal motif of unknown function that is present in all winged helix Class II transcription factors. A phylogenetic analysis of the DNA binding domains shows that, within the Class II, Spfkh1 groups with the deuterostomes as opposed to the protostomes. Analysis of the sequence 5' to the start of translation revealed binding sites for a large number of different transcription factors, many of which are present in multiple copies. The constellation of binding sites in the cis-regulatory region indicates that Spfkh1 is regulated by a complex set of factors, some of which are known to be endoderm specific. Included among these are binding sites for factors downstream of the Wnt/beta-catenin and hedgehog signaling pathways, implicating these pathways in both regulation of Spfkh1 and specification of endoderm.

MGA2 or SPT23 is required for transcription of the delta9 fatty acid desaturase gene, OLE1, and nuclear membrane integrity in Saccharomyces cerevisiae

MGA2 and SPT23 are functionally and genetically redundant homologs in Saccharomyces cerevisiae. Both genes are implicated in the transcription of a subset of genes, including Ty retrotransposons and Ty-induced mutations. Neither gene is essential for growth, but mga2 spt23 double mutants are inviable. We have isolated a gene-specific activator, SWI5, and the Delta9 fatty acid desaturase of yeast, OLE1, as multicopy suppressors of an mga2Delta spt23 temperature-sensitive mutation (spt23-ts). The level of unsaturated fatty acids decreases 35-40% when the mga2Delta spt23-ts mutant is incubated at 37 degrees. Electron microscopy of these cells reveals a separation of inner and outer nuclear membranes that is sometimes accompanied by vesicle-like projections in the intermembrane space. The products of Ole1p catalysis, oleic acid and palmitoleic acid, suppress mga2Delta spt23-ts and mga2Delta spt23Delta lethality and restore normal nuclear membrane morphology. Furthermore, the level of the OLE1 transcript decreases more than 15-fold in the absence of wild-type Mga2p and Spt23p. Our results suggest that Mga2p/Spt23p control cell viability by stimulating OLE1 transcription.

Modulation of lipid unsaturation and membrane fluid state in mammalian cells by stable transformation with the delta9-desaturase gene of Saccharomyces cerevisiae

The composition and physical state of membrane lipids determine the dynamic nature of membranes, which in turn, could directly be linked to the activity of various membrane-associated cellular functions. To better understand the molecular basis of different membrane-related phenomena we established a novel strategy to alter unsaturation of mammalian cell membranes with an identical genetic background. We transfected L929 mouse fibroblastoid cells with DNA constructs containing the Delta9-fatty acid desaturase gene (Ole1) of S. cerevisiae under the control of desaturase promoters derived either from wild type or mutant strains of the dimorphic fungus H. capsulatum.