Supposedly identical microplastic particles substantially differ in their material properties influencing particle-cell interactions and cellular responses

Microplastics and its putative adverse effects on environmental and human health increasingly gain scientific and public attention. Systematic studies on the effects of microplastics are currently hampered by using rather poorly characterised particles, leading to contradictory results for the same particle type. Here, surface properties and chemical composition of two commercially available nominally identical polystyrene microparticles, frequently used in effect studies, were characterised. We show distinct differences in monomer content, ζ-potentials and surface charge densities. Cells exposed to particles showing a lower ζ-potential and a higher monomer content displayed a higher number of particle-cell-interactions and consequently a decrease in cell metabolism and proliferation, especially at higher particle concentrations. Our study emphasises that no general statements can be made about the effects of microplastics, not even for the same polymer type in the same size class, unless the physicochemical properties are well characterised.

Use of the mitochondria toxicity assay for quantifying the viable cell density of microencapsulated jurkat cells

The mitochondria toxicity assay (MTT assay) is an established method for monitoring cell viability based on mitochondrial activity. Here the MTT assay is proposed for the in situ quantification of the living cell density of microencapsulated Jurkat cells. Three systems were used to encapsulate the cells, namely a membrane consisting of an interpenetrating polyelectrolyte network of sodium cellulose sulphate/poly(diallyldimethylammonium chloride) (NaCS/PDADMAC), a calcium alginate hydrogel covered with poly(L-lysine) (Ca-alg-PLL), and a novel calcium alginate-poly(ethylene glycol) hybrid material (Ca-alg-PEG). MTT results were correlated to data obtained by the trypan blue exclusion assay after release of the cells from the NaCS/PDADMAC and Ca-alg-PLL capsules, while a resazurin-based assay was used for comparison in case of the Ca-alg-PEG material. Analysis by MTT assay allows quick and reliable determination of viable cell densities of encapsulated cells independent of the capsule material. The assay is highly reproducible with inter-assay relative standard deviations below 10%.

Direct detection of formaldehyde in air by a novel NAD+- and glutathione-independent formaldehyde dehydrogenase-based biosensor

An amperometric enzyme-based sensor-system for the direct detection of formaldehyde in air is under investigation. The biosensor is based on a native bacterial NAD(+)- and glutathione-independent formaldehyde dehydrogenase as biorecognition element. The enzyme was isolated from Hyphomicrobium zavarzinii strain ZV 580, grown on methylamine hydrochloride in a fed-batch process. The sensor depends on the enzymatic conversion of the analyte to formic acid. Released electrons are detected in an amperometric measurement at 0.2V vs. Ag/AgCl reference electrode by means of a redox-mediator. To optimize the sensing device, Ca(2+) and pyrroloquinoline quinone (PQQ) were added to the buffer solution as reconstitutional substances. At this stage, the sensor shows linear response in the tested ppm-range with a sensitivity of 0.39 microA/ppm. The signal is highly reproducible with respect to sensitivity and base line signal. Reproducibility of sensitivity is more than 90% within the same bacterial batch and even when enzyme of different bacterial batches is used.

Targeting of adenovirus to endothelial cells by a bispecific single-chain diabody directed against the adenovirus fiber knob domain and human endoglin (CD105)

The use of adenoviruses for antivascular cancer gene therapy is limited by their low transduction efficiency for endothelial cells. We have developed a recombinant bispecific antibody as a molecular bridge, linking the adenovirus capsid to the endothelial cell surface protein endoglin, for vascular targeting of adenoviruses. Endoglin (CD105), a component of the transforming growth factor beta receptor complex, represents a promising target for antivascular cancer therapy. Endoglin is expressed predominantly on endothelial cells and is upregulated in angiogenic areas of tumors. We isolated single-chain Fv fragments directed against human endoglin from a human semisynthetic antibody library. One of the isolated scFv fragments (scFv C4) bound specifically to various proliferating primary endothelial cells or cell lines including HUVEC, HDMEC, HMVEC, and HMEC. ScFv C4 was therefore used to construct a bispecific single-chain diabody directed against endoglin and the adenovirus fiber knob domain (scDb EDG-Ad). This bispecific molecule mediated enhanced and selective adenovirus transduction of HUVECs, which was independent from binding to the coxsackievirus and adenovirus receptor (CAR) and alpha(v)-integrins. Thus, adenovirus infection was redirected to a new cellular receptor (CD105) and cell entry pathway. These results demonstrate the utility of bispecific single-chain diabodies, which can be produced in large quantities in bacteria, for the retargeting of adenoviruses in cancer gene therapy.

A synthetic leucine zipper-based dimerization system for combining multiple promoter specificities

One of the biggest challenges facing gene therapy is the development of vectors that direct the activity of therapeutic genes specifically to the sites of disease. To achieve this goal, the restriction of transgene transcription via synthetic promoters that are endowed with multiple specificities represents a particularly promising strategy. Towards this end, we have developed a generally applicable strategy (DCTF system) where a synthetic promoter is driven by an artificial heterodimeric transcription factor whose DNA-binding and transactivating subunits are expressed from two promoters with different selectivity. A crucial determinant of the DCTF system is the heterodimerization interface that should provide for a high affinity interaction without interference by endogenous proteins. Here, we describe such a dimerization system based on engineered Fos and Jun leucine zippers. We show the usefulness of this system for the combination of cell type-specific and cell cycle-regulated transcription and demonstrate its functionality in an in vivo setting.

Gene therapy: designer promoters for tumour targeting

One of the biggest challenges facing cancer therapy is to generate tumour-specific treatment strategies. Gene therapy hopes to achieve this by directing the activity of therapeutic genes specifically to the sites of disease. Of paramount importance for the success of this approach is the availability of tumour-specific delivery systems: both the transductional targeting of the vector vehicle and the restriction of transgene expression to the tumour are promising strategies towards this goal. This review will focus on the recent achievements in the field of transcriptional targeting and the different strategies to improve or design promoters with the desired specificities.

A dual specificity promoter system combining cell cycle-regulated and tissue-specific transcriptional control

The expression of both proliferation-associated and cell type-specific genes is a hallmark of both cancer cells and tumor endothelial cells. The possibility to combine both features in a single transcriptional control unit would greatly increase the selectivity of vectors used for cancer gene therapy. Previous studies by our laboratory have shown that the transcription of several cell cycle genes is regulated by a novel cell cycle-regulated repressor, termed CDF-1. This repressor functions by blocking in resting cells the transcriptional activation by specific factors binding to the upstream activating sequence (UAS), most notably the CCAAT-box binding factor NF-Y/CBF. Based on this work we have developed a dual specificity promoter system that combines cell type specificity with cell cycle regulation. A chimeric transcription factor (Gal4/NF-Y) consisting of the transactivation domain of NF-Y and the DNA-binding domain of Gal4 is expressed from a tissue-specific promoter. Gal4/NF-Y can bind to a second promoter consisting of a minimal cyclin A promoter with multiple Gal4 binding sites replacing the normal UAS. This leads to the tissue-specific expression of Gal4/NF-Y whose stimulatory activity on the promoter is restrained in resting cells by the recruitment of the CDF-1 repressor to the promoter. The functionality of this system is demonstrated for the specific transcriptional targeting of proliferating melanoma cells, where cell cycle regulation was >20-fold and cell type specificity was >50-fold.

Tissue-specific, cell cycle-regulated chimeric transcription factors for the targeting of gene expression to tumor cells

A major challenge in the gene therapy of proliferative diseases is the specific targeting of gene expression. Here we describe a new approach based on the development of dual-specificity promoters that are both cell type specific and cell cycle regulated. The gene of interest is driven by an artificial heterodimeric transcription factor, whose DNA-binding subunit is expressed from a tissue-specific promoter, whereas the trans-activating subunit is transcribed from a cell cycle-regulated promoter. As a result gene expression occurs preferentially in the proliferating cells of a specific type of tissue. The selectivity of this strategy is demonstrated for the expression of a transgene in proliferating melanoma cells, using a combination of cyclin A and tyrosinase promoter elements. We also show that the level of expression that can be achieved by this system is sufficient to induce a clear biological effect in a TNF-alpha cytotoxicity assay.

A strategy for enhancing the transcriptional activity of weak cell type-specific promoters

Cell type- and tissue-specific promoters play an important role in the development of site-selective vectors for gene therapy. A large number of highly specific promoters has been described, but their applicability is often hampered by their inefficient transcriptional activity. In this study, we describe a new strategy for enhancing the activity of weak promoters without loss of specificity. The basic principle of this strategy is to establish a positive feedback loop which is initiated by transcription from a cell type-specific promoter. This was achieved by using a cell type-specific promoter to drive the simultaneous expression of the desired effector/reporter gene product and a strong artificial transcriptional activator which stimulates transcription through appropriate binding sites in the promoter. Using a VP16-LexA chimeric transcription factor, we show that this approach leads to a 14- to > 100-fold enhancement of both the endothelial cell-specific von Willebrand factor promoter and the gastrointestinal-specific sucrase-isomaltase promoter while maintaining approximately 30- to > 100-fold cell type specificity.

CDF-1 mediated repression of cell cycle genes targets a specific subset of transactivators

The cdc25C, cyclin A and cdc2 genes are regulated during the cell cycle through two contiguous repressor binding sites, the CDE and CHR, located in the region of transcription initiation and interacting with a factor termed CDF-1. The target of this repression seems to be transcriptional activation of these promoters by transcription factors bound upstream. The majority of these factors falls into the class of glutamine-rich activators, suggesting that CDF-1-mediated repression might be activation domain specific. In the present study we have used chimeric promoter constructs to demonstrate that the cdc25C UAS, but not the core promoter, is crucial for repression. In addition, we show that only specific transcription factors and activation domains are responsive to CDE-CHR-mediated cell cycle regulation. These observations clearly indicate that CDF-1 interferes with activation of transcription by a specific subset of transactivators. The repressible activation domains belong to the same class of glutamine-rich activators, pointing to specific interactions of CDF-1 with components of the transcription machinery. In agreement with this conclusion we find that a simple inversion of the CDF-CHR module completely abrogates cell cycle-regulated repression.

CDF-1-mediated repression of cell cycle genes targets a specific subset of transactivators

The cdc25C , cyclin A and cdc2 genes are regulated during the cell cycle through two contiguous repressor binding sites, the CDE and CHR, located in the region of transcription initiation and interacting with a factor termed CDF-1. The target of this repression seems to be transcriptional activation of these promoters by transcription factors bound upstream. The majority of these factors falls into the class of glutamine-rich activators, suggesting that CDF-1-mediated repression might be activation domain specific. In the present study we have used chimeric promoter constructs to demonstrate that the cdc25C UAS, but not the core promoter, is crucial for repression. In addition, we show that only specific transcription factors and activation domains are responsive to CDE-CHR-mediated cell cycle regulation. These observations clearly indicate that CDF-1 interferes with activation of transcription by a specific subset of transactivators. The repressible activation domains belong to the same class of glutamine-rich activators, pointing to specific interactions of CDF-1 with components of the transcription machinery. In agreement with this conclusion we find that a simple inversion of the CDE-CHR module completely abrogates cell cycle-regulated repression.

Cell cycle regulation of the chicken hsp90 alpha expression

The heat-shock protein of 90 kDa (hsp90), constitutively expressed in most cells, is up-regulated by thermal stress and by developmental and mitogenic stimuli. When the serum-starved chicken hepatoma cell line DU249 is stimulated by serum, insulin, or growth factors acting via tyrosine kinase receptors, a transient induced expression of the hsp90 alpha gene takes place at both the messenger RNA and the protein synthesis level. This response is protein synthesis dependent and DNA synthesis independent. The maximum level of hsp90 alpha mRNA accumulation always precedes the maximum level of thymidine incorporation, suggesting a possible link between cell cycle and hsp90 alpha regulation (Jérôme, V., J. Léger, J. Devin, E.E. Baulieu, and M. G. Catelli. Growth Factors 4:317-327, 1991). Herein, we examine the subcellular distribution of hsp90 and the cell cycle-dependent regulation of the hsp90 alpha mRNA level. We show that, in contrast to hsp70, the 35S metabolically-labeled hsp90, which accumulates in the cytosoluble fraction 6 to 8 h after serum treatment, is not preferentially translocated to the nuclear compartment, although a small fraction is always present in the nucleus. We also demonstrated that serum- or insulin-induced accumulation of hsp90 alpha mRNA results from an activation of gene transcription and that hsp90 alpha promotor activity, which is low in quiescent DU249 cells, is induced approximately fivefold after serum stimulation. Finally, in cell culture synchronized by nocodazole or aphidicholin, hsp90 alpha mRNA accumulation seems an event specific to G1/S transition.

Cloning of chicken hsp90 beta: the only vertebrate hsp90 insensitive to heat shock

The cloning of chicken hsp90 beta, reported here, supports the hypothesis that the hsp90 alpha and beta genes are the result of a gene duplication event that occurred at the time of the emergence of vertebrates. Avian hsp90 beta mRNA is not inducible by thermal stress contrary to the mouse and human hsp90 alpha and beta mRNAs. Moreover, hsp90 beta mRNA level is not increased by mitogenic stimuli, like serum or insulin, which induce hsp90 alpha mRNA. Different functions and regulations of hsp90 alpha and beta will be probably more easily understood in the avian species than in higher vertebrates.

Growth factors acting via tyrosine kinase receptors induce HSP90 alpha gene expression

Hsp90 is a heat-shock protein constitutively expressed in most cells. Besides regulation by thermal stress, the expression of hsp90 is also positively regulated by developmental and mitogenic stimuli. The effect of serum and insulin on protein and hsp90 alpha-mRNA levels has been studied in the chicken hepatoma cell line DU249. The culture of cells in serum-free medium resulted in a decrease of hsp90 alpha-mRNA level. A transient increase was observed at 6-9 h after serum restimulation. The expression of hsp90 gene was also increased by insulin alone in a dose-dependent manner and was maximum between 6 and 9 h treatment. The insulin induced increase of hsp90 alpha-mRNA was suppressed by cycloheximide (10 micrograms/ml) but not by an inhibitor of DNA synthesis, demonstrating that this induction requires protein neosynthesis. In serum starved cells, other growth factors (IGF1, EGF and bFGF) showed a positive effect on hsp90 alpha-mRNA level which took place before DNA synthesis with the same time-course as that of insulin. With PDGF, the induction of hsp90 alpha-mRNA occurred earlier. The time interval between the maximum of hsp90 alpha-mRNA induction and that of DNA synthesis was the same for all growth factors studied. From these results, we conclude that growth factors acting via tyrosine kinase receptors up-regulate hsp90 alpha-mRNA level in a DNA synthesis independent manner, possibly in late G1.

Isolation and functional analysis of chicken 90-kDa heat shock protein gene promoter

We report the nucleotide sequence of a 2652 bp derived from a chicken 90-kDa heat shock protein (hsp 90) genomic clone. This fragment contains 890 bp of the 5' flanking region and 1762 bp of structural gene sequence encoding the first 85 amino acids of the protein. The start site of transcription was determined by primer extension and RNase mapping. Two introns have been identified. The first intron presents two features in common with the unique intron of the hsp 83 of drosophila: its location just before the ATG initiation codon and its length of approximately 1.3 Kb. The 5' flanking region contains a TATAA element, a CCAAT box and several putative cis-regulatory elements that might account for the basal level of expression and developmental regulation of the gene. Functional analyses show that hsp 90 gene expression is constitutive and heat inducible and that a full heat shock response requires the cooperativity of two distinct blocks of overlapping heat shock response elements.