Identical cis-acting elements and related trans-acting factors control activity of nonviral promoter in Schizosaccharomyces pombe and mammalian cells

Reciprocal relation between reporter gene transcription and translation efficiency in fission yeast

The fission yeast, Schizosaccharomyces pombe, is an excellent model for basic research but is not useful for commercial scale protein expression due to lack of strong expression vectors. Earlier, we showed that the lsd90 promoter elicited significantly greater GFP expression level than the adh1 and nmt1 promoters, albeit in different vector backbones. Here, we have systematically investigated the contribution of selectable markers, LEU2 and URA3m to GFP expression: while LEU2 elicited very low expression, the URA3m gene, with truncated promoter, elicited much greater GFP expression level with all promoters. Paradoxically, an inverse correlation was observed between the GFP transcription and translation efficiency. This system can be useful for understanding the factors governing recombinant gene expression and optimization of protein production.

The helicase-like transcription factor (HLTF) in cancer: loss of function or oncomorphic conversion of a tumor suppressor?

The Helicase-like Transcription Factor (HLTF) belongs to the SWI/SNF family of proteins involved in chromatin remodeling. In addition to its role in gene transcription, HLTF has been implicated in DNA repair, which suggests that this protein acts as a tumor suppressor. Accumulating evidence indicates that HLTF expression is altered in various cancers via two mechanisms: gene silencing through promoter hypermethylation or alternative mRNA splicing, which leads to the expression of truncated proteins that lack DNA repair domains. In either case, the alteration of HLTF expression in cancer has a poor prognosis. In this review, we gathered published clinical and molecular data on HLTF. Our purposes are (a) to address whether HLTF alterations could be considered as cancer drivers or passengers and (b) to determine whether its different functions (transcription or DNA repair) could be diverted in clonal selection during cancer progression.

Biotechnological synthesis of drug metabolites using human cytochrome P450 isozymes heterologously expressed in fission yeast

Cytochrome P450 mono-oxygenases (CYPs) are the major enzymes involved in the metabolism of drugs and poisons in humans. The variation of their activity - due to genetic polymorphisms or enzyme inhibition/induction - potentially increases the risk of side effects or toxicity. Studies on CYP-dependent metabolism are important in drug-development or toxicity studies. Reference standards of drug metabolites required for such studies, especially in the context of metabolites in safety testing (MIST), are often not commercially available and their classical chemical synthesis can be cumbersome. Recently, a biotechnological approach using human CYP isozymes heterologously expressed in fission yeast was developed for the synthesis of drug metabolites. Among other aspects, this approach has the distinct advantages that the reactions run under mild conditions and that only the final product must be isolated and characterized. This review overviews the first practical applications of this new approach and discusses the selection of substrates, metabolites and fission yeast strains as well as important aspects of incubation, product isolation and clean-up.

Biotechnological synthesis of drug metabolites using human cytochrome P450 2D6 heterologously expressed in fission yeast exemplified for the designer drug metabolite 4′-hydroxymethyl-α-pyrrolidinobutyrophenone

The aim of this study was evaluating the principle feasibility of biotechnological synthesis of drug metabolites using heterologously expressed human cytochrome P450 (CYP) enzymes. Human CYP2D6 expressed in fission yeast (Schizosaccharomyces pombe) strain CAD58 was used as model enzyme and the designer drug 4'-methyl-alpha-pyrrolidinobutyrophenone (MPBP) as model drug. For synthesis of 4'-hydroxmethyl-alpha-pyrrolidinobutyrophenone (HO-MPBP), 250 micromol of MPBP.HNO(3) were incubated with one litre of CAD58 culture (10(8)cells/mL, pH 9, 48 h, 30 degrees C). HO-MPBP was isolated by liquid-liquid extraction and precipitated as its hydrochloride salt. Identity and purity of the product were tested by HPLC with ultraviolet (UV) detection, GC-MS, and (1)H-NMR. CAD58 was further characterized regarding the influence of incubation pH (5-10), cell density (10(7)-10(8)cells/mL), and incubation time (0-120 h) on metabolite formation using the substrates dextromethorphan and MPBP. The preparative experiment yielded 40 mg (141mumol) of HO-MPBP.HCl with a purity of >98%. In the characterization experiments, the metabolite formation rate peaked at pH 8. A linear relationship was observed between cell density and metabolite formation (R(2)>0.996). The rate of metabolite formation was slower in the earlier stages of incubation but then increased. For HO-MPBP, it became constant in the time interval of 2.5-34 h (R(2)>998).

A truncated derivative of nmt 1 promoter exhibits temperature-dependent induction of gene expression in Schizosaccharomyces pombe

Despite increasing exploitation of Schizosaccharomyces pombe as a model system there is a lack of convenient vectors for research and application. Expression with the commonly used promoter, nmt 1, requires a laborious regime involving the removal of repressor, thiamine, from a growing culture and further growth for 18 h to achieve maximum expression, thus underlining the need for more user-friendly promoters. We report here the isolation and characterization of a truncated derivative of the nmt 1 promoter having novel induction characteristics: it is induced by shift of growth temperature from 36 degrees C to 25 degrees C, achieving maximum expression within 3 h. Similar features of expression were observed with the reporter genes GFP and beta-galactosidase, a native gene, cdc 18, and a commercially important foreign therapeutic protein, streptokinase. The new promoter element offers additional advantages, such as lack of deleterious effect on cell viability and potential ability to express toxic proteins. These features make the new promoter a potentially better alternative to nmt 1, both as a research tool and for expression of commercially important proteins in Sz. pombe, and suggest the possibility of using similar approaches to design promoters with novel and useful properties.

Comparison of different signal peptides for secretion of heterologous proteins in fission yeast

In the fission yeast Schizosaccharomyces pombe, there are relatively few signal peptides available and most reports of their activity have not been comparative. Using sequence information from the S. pombe genome database we have identified three putative signal peptides, designated Cpy, Amy and Dpp, and compared their ability to support secretion of green fluorescent protein (GFP). In the comparison we also included the two well-described secretion signals derived from the precursors of, respectively, the Saccharomyces cerevisiae alpha-factor and the S. pombe P-factor. The capability of the tested signal peptides to direct secretion of GFP varied greatly. The alpha-factor signal did not confer secretion to GFP and all the produced GFP was trapped intracellular. In contrast, the Cpy signal peptide supported efficient secretion of GFP with yields approximating 10 mg/L. We also found that the use of an attenuated version of the S. cerevisiae URA3 marker substantially increases vector copy number and expression yield in fission yeast.

In vitro transcription and start site selection in Schizosaccharomyces pombe

We have used the fission yeast Schizosaccharomyces pombe to establish both a biochemical and genetic system to study the roles of general transcription factors in transcription initiation. Extracts were prepared that faithfully transcribed S. pombe promoters and the results confirm that, in contrast to the budding yeast Saccharomyces cerevisiae, in vitro transcription in S. pombe initiates near to the TATA element. S. pombe transcription relies on upstream activation sequence elements and these can be replaced successfully with sites for binding Gal4-VP16 activators. Although it is mammalian-like in these respects, S. pombe initiation uses an unusual scanning mechanism. This directs initiation, preferentially using purines, within a narrow window approximately 25-40 base-pairs downstream from the edge of the TATA element. Genetic experiments showed that this scanning mechanism was associated with the properties of the TFIIB polypeptide. When human TFIIB was expressed in S. pombe, it was accepted by the endogenous transcription machinery and caused initiation to be restricted to the closer edge of this window, corresponding to the distance in humans. Preliminary experiments suggested that S. cerevisiae TFIIB was not accepted. The results enlarge the potential for using fission yeast to study the properties of general transcription factors such as TFIIB in choosing the sites at which transcription initiates.

A novel expression cloning method to isolate mammalian transcription factors in Schizosaccharomyces pombe

We describe a novel expression cloning strategy in the fission yeast for the isolation of mammalian transcription factors using a mammalian promoter as target. This strategy is possible because of the conservation between mammalian cells and Schizosaccharomyces pombe of the mechanism that leads to the selection of the transcription start site. It also opens new perspectives to investigate the transcriptional regulation of genes for which detailed promoter analysis is difficult.