ONLY A SMALL FRACTION OF CELLS PRODUCE ASSEMBLED CAPSIDS DURING TRANSFECTION-BASED MANUFACTURING OF ADENO-ASSOCIATED VIRUS VECTORS

Plasmid transfection of mammalian cells is the dominant platform used to produce adeno‐associated virus (AAV) vectors for clinical and research applications. Low yields from this platform currently make it difficult to supply these activities with adequate material. In an effort to better understand the current limitations of transfection‐based manufacturing, this study examines what proportion of cells in a model transfection produce appreciable amounts of assembled AAV capsid. Using conformation‐specific antibody staining and flow cytometry, we report the surprising result that despite obtaining high transfection efficiencies and nominal vector yields in our model system, only 5%–10% of cells appear to produce measurable levels of assembled AAV capsids. This finding implies that considerable increases in vector titer could be realized through increasing the proportion of productive cells. Furthermore, we suggest that the flow cytometry assay used here to quantify productive cells may be a useful metric for future optimization of transfection‐based AAV vector manufacturing platforms.

Assisted Design of Antibody and Protein Therapeutics (ADAPT)

Effective biologic therapeutics require binding affinities that are fine-tuned to their disease-related molecular target. The ADAPT (Assisted Design of Antibody and Protein Therapeutics) platform aids in the selection of mutants that improve/modulate the affinity of antibodies and other biologics. It uses a consensus z-score from three scoring functions and interleaves computational predictions with experimental validation, significantly enhancing the robustness of the design and selection of mutants. The platform was tested on three antibody Fab-antigen systems that spanned a wide range of initial binding affinities: bH1-VEGF-A (44 nM), bH1-HER2 (3.6 nM) and Herceptin-HER2 (0.058 nM). Novel triple mutants were obtained that exhibited 104-, 46- and 32-fold improvements in binding affinity for each system, respectively. Moreover, for all three antibody-antigen systems over 90% of all the intermediate single and double mutants that were designed and tested showed higher affinities than the parent sequence. The contributions of the individual mutants to the change in binding affinity appear to be roughly additive when combined to form double and triple mutants. The new interactions introduced by the affinity-enhancing mutants included long-range electrostatics as well as short-range nonpolar interactions. This diversity in the types of new interactions formed by the mutants was reflected in SPR kinetics that showed that the enhancements in affinities arose from increasing on-rates, decreasing off-rates or a combination of the two effects, depending on the mutation. ADAPT is a very focused search of sequence space and required only 20-30 mutants for each system to be made and tested to achieve the affinity enhancements mentioned above.

Rapid protein production from stable CHO cell pools using plasmid vector and the cumate gene-switch

To rapidly produce large amounts of recombinant proteins, the generation of stable Chinese Hamster Ovary (CHO) cell pools represents a useful alternative to large-scale transient gene expression (TGE). We have developed a cell line (CHO^BRI/rcTA) allowing the inducible expression of recombinant proteins, based on the cumate gene switch. After the identification of optimal plasmid DNA topology (supercoiled vs linearized plasmid) for PEIpro™ mediated transfection and of optimal conditions for methionine sulfoximine (MSX) selection, we were able to generate CHO^BRI/rcTA pools producing high levels of recombinant proteins. Volumetric productivities of up to 900mg/L were reproducibly achieved for a Fc fusion protein and up to 350mg/L for an antibody after 14days post-induction in non-optimized fed-batch cultures. In addition, we show that CHO pool volumetric productivities are not affected by a freeze-thaw cycle or following maintenance in culture for over one month in the presence of MSX. Finally, we demonstrate that volumetric protein production with the CR5 cumate-inducible promoter is three- to four-fold higher than with the human CMV or hybrid EF1α-HTLV constitutive promoters. These results suggest that the cumate-inducible CHO^BRI/rcTA stable pool platform is a powerful and robust system for the rapid production of gram amounts of recombinant proteins.

Critical assessment of influenza VLP production in Sf9 and HEK293 expression systems

Background

Each year, influenza is responsible for hundreds of thousand cases of illness and deaths worldwide. Due to the virus’ fast mutation rate, the World Health Organization (WHO) is constantly on alert to rapidly respond to emerging pandemic strains. Although anti-viral therapies exist, the most proficient way to stop the spread of disease is through vaccination. The majority of influenza vaccines on the market are produced in embryonic hen’s eggs and are composed of purified viral antigens from inactivated whole virus. This manufacturing system, however, is limited in its production capacity. Cell culture produced vaccines have been proposed for their potential to overcome the problems associated with egg-based production. Virus-like particles (VLPs) of influenza virus are promising candidate vaccines under consideration by both academic and industry researchers.

Methods

In this study, VLPs were produced in HEK293 suspension cells using the Bacmam transduction system and Sf9 cells using the baculovirus infection system. The proposed systems were assessed for their ability to produce influenza VLPs composed of Hemagglutinin (HA), Neuraminidase (NA) and Matrix Protein (M1) and compared through the lens of bioprocessing by highlighting baseline production yields and bioactivity. VLPs from both systems were characterized using available influenza quantification techniques, such as single radial immunodiffusion assay (SRID), HA assay, western blot and negative staining transmission electron microscopy (NSTEM) to quantify total particles.

Results

For the HEK293 production system, VLPs were found to be associated with the cell pellet in addition to those released in the supernatant. Sf9 cells produced 35 times more VLPs than HEK293 cells. Sf9-VLPs had higher total HA activity and were generally more homogeneous in morphology and size. However, Sf9 VLP samples contained 20 times more baculovirus than VLPs, whereas 293 VLPs were produced along with vesicles.

Conclusions

This study highlights key production hurdles that must be overcome in both expression platforms, namely the presence of contaminants and the ensuing quantification challenges, and brings up the question of what truly constitutes an influenza VLP candidate vaccine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0152-x) contains supplementary material, which is available to authorized users.

Abstract 659: Integrated therapeutic antibody development at the National Research Council of Canada

Advances in genomics and antibody engineering have enabled the development of an innovative class of targeted therapies, namely therapeutic antibodies, for the treatment of diseases with significant unmet medical needs such as cancer. Therapeutic antibodies represent one of the largest and fastest growing classes of medications. The National Research Council of Canada (NRC) has built a chain of cutting edge technology platforms needed to discover, engineer and produce therapeutic monoclonal antibodies with the goal of partnering with industrial and academic centers to advance research and development of this important class of therapeutics.

Target Identification- Tumor targets were identified using a combination of proteomics, transcriptomics and bioinformatic approaches. Out of these lists, approximately 40 tumor targets were selected and over 3,000 antibodies of mouse and camelid origin were generated against these targets.

Antibody generation can be done conventionally, using the recombinant target protein produced using NRC's high efficiency cell expression platforms in CHO or HEK293 cells or by direct immunization with plasmid DNA constructs. Clone selection is carried out by ELISA and typically 50 antibodies/target are identified for further characterization.

Antibody characterization and validation- The affinities of the antibodies are determined by SPR biosensor analysis. Epitope mapping can be carried out so that representative antibodies can be selected for further validation in appropriate cell-based assays (many of which are established at NRC) and animal models.

Therapeutic antibody Optimization, Bioprocessing and Biomanufacturing- Therapeutic antibodies selected for development can be further optimized using antibody engineering technologies to humanize them and/or modify their glycosylation patterns to improve their effector function, pharmacokinetics, solubility and stability as well as reduce their immunogenicity. The NRC platform for large scale protein production has the capacity to manufacture up to 500 g of commercial grade antibody in a cGMP certified CHO cell line which is ready for transfer to CMOs .

Citation Format: Maria L. Jaramillo, Anne Marcil, Yves Durocher, Renald Gilbert, Alaka Mullick, John Kelly, Maureen O'Connor-McCourt, Bernard Massie. Integrated therapeutic antibody development at the National Research Council of Canada. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 659. doi:10.1158/1538-7445.AM2014-659

Genetic control of susceptibility to Candida albicans in SM/J mice

In the immunocompromised host, invasive infection with the fungal pathogen Candida albicans is associated with high morbidity and mortality. Sporadic cases in otherwise normal individuals are rare, and they are thought to be associated with genetic predisposition. Using a mouse model of systemic infection with C. albicans, we identified the SM/J mouse strain as unusually susceptible to infection. Genetic linkage studies in informative [C57BL/6JxSM/J]F2 mice identified a major locus on distal chromosome 15, given the appellation Carg5, that regulates C. albicans replication in SM/J mice. Cellular and molecular immunophenotyping experiments, as well as functional studies in purified cell populations from SM/J and C57BL/6J, and in [C57BL/6JxSM/J]F2 mice fixed for homozygous or heterozygous Carg5 alleles, indicate that Carg5-regulated susceptibility in SM/J is associated with a complex defect in the myeloid compartment of these mice. SM/J neutrophils express lower levels of Ly6G, and importantly, they show significantly reduced production of reactive oxygen species in response to stimulation with fMLF and PMA. Likewise, CD11b(+)Ly6G(-)Ly6C(hi) inflammatory monocytes were present at lower levels in the blood of infected SM/J, recruited less efficiently at the site of infection, and displayed blunted oxidative burst. Studies in F2 mice establish strong correlations between Carg5 alleles, Ly6G expression, production of serum CCL2 (MCP-1), and susceptibility to C. albicans. Genomic DNA sequencing of chromatin immunoprecipitated for myeloid proinflammatory transcription factors IRF1, IRF8, STAT1 and NF-κB, as well as RNA sequencing, were used to develop a "myeloid inflammatory score" and systematically analyze and prioritize potential candidate genes in the Carg5 interval.

Abstract A248: Integrated therapeutic antibody development at the National Research Council of Canada

Advances in genomics and antibody engineering have enabled the development of an innovative class of targeted therapies, namely therapeutic antibodies, for the treatment of diseases with significant unmet medical needs such as cancer. Therapeutic antibodies represent one of the largest and fastest growing classes of medications. The NRC has built a chain of cutting edge technology platforms needed to discover, engineer and produce therapeutic monoclonal antibodies with the goal of partnering with industrial and academic centers to advance research and development of this important class of therapeutics.

Target Identification- To establish and validate the technology platforms, tumor targets for candidate therapeutic antibody production were identified using a combination of proteomics, transcriptomics and bioinformatic approaches. Out of these lists, approximately 40 tumor targets were selected (known therapeutic antibody targets were excluded), and over 3,000 antibodies of mouse and camelid origin were then generated against these targets.

Antibody generation- Once identified, the recombinant target protein of interest was produced using the NRC's high efficiency cell expression platforms in CHO or HEK293 cells and purified protein was used for immunization or panning. For targets which were difficult to express or purify, the capabilities for direct immunization with plasmid DNA constructs were utilized. Clone selection was carried out by ELISA and typically 50 antibodies/target were identified for further characterization.

Antibody characterization and validation- The affinities of the antibodies were determined by SPR biosensor analysis. Reverse phase protein arrays and Western blot analysis on protein mixes and cell line extracts allowed the characterization of the specificity of the antibodies. SPR-based epitope binning was carried out in order to characterize the diversity of the antibody collections and to enable the selection of representative antibodies from each epitope bin for further analysis. Select antibodies were assessed in appropriate cell-based assays for prioritization based on function.

Therapeutic antibody Optimization, Bioprocessing and Biomanufacturing- Therapeutic antibodies selected for development can be further optimized using antibody engineering technologies to humanize them and/or modify their glycosylation patterns to improve their effector function, pharmacokinetics, solubility and stability as well as reduce their immunogenicity. The NRC platform for large scale protein production has the capacity to manufacture up to 500 g of commercial grade antibody using serum free, low endotoxin media in a cGMP certified CHO cell line which is ready for transfer to CMOs or other industrial partners.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A248.

Citation Format: Maria L. Jaramillo, Anne Marcil, Yves Durocher, Renald Gilbert, Alaka Mullick, John Kelly, Maureen O'Connor-McCourt, Bernard Massie. Integrated therapeutic antibody development at the National Research Council of Canada. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A248.

A novel role for the fifth component of complement (C5) in cardiac physiology

We have previously demonstrated that C5-deficient A/J and recombinant congenic BcA17 mice suffer from cardiac dysfunction when infected with C. albicans blastospores intravenously. During these studies we had observed that, even in the control un-infected state, BcA17 hearts displayed alterations in gene expression that have been associated with pathological cardiac hypertrophy in comparison to parental C5-sufficient C57Bl/6J (B6) mice. Of note was an increase in the expression of Nppb, a member of the fetal gene program and a decrease in the expression of Rgs2, an inhibitor of the hypertrophic response. We now report that C5-deletion has also affected the expression of other elements of the fetal gene program. Moreover deleting the C5a receptor, C5aR, has essentially the same effect as deleting C5, indicating a key role for C5a-C5aR signaling in the phenotype. Having noted a pathological phenotype in the un-infected state, we investigated the role of C5 in the response to cardiac stress. In previous studies, comparison of the expression profiles of C. albicans-infected BcA17 and similarly infected B6 hearts had revealed a paucity of cardioprotective genes in the C5-deficient heart. To determine whether this was also directly linked to C5-deficiency, we tested the expression of 5 such genes in the C. albicans-infected C5aR(-/-) mice. We found again that deletion of C5aR recapitulated the alterations in stress response of BcA17. To determine whether our observations were relevant to other forms of cardiac injury, we tested the effect of C5-deficiency on the response to isoproterenol-induced hypertrophic stimulation. Consistent with our hypothesis, A/J, BcA17 and C5aR(-/-) mice responded with higher levels of Nppa expression than B6 and BALB/c mice. In conclusion, our results suggest that an absence of functional C5a renders the heart in a state of distress, conferring a predisposition to cardiac dysfunction in the face of additional injury.

Genetic control of susceptibility to infection with Candida albicans in mice

Candida albicans is an opportunistic pathogen that causes acute disseminated infections in immunocompromised hosts, representing an important cause of morbidity and mortality in these patients. To study the genetic control of susceptibility to disseminated C. albicans in mice, we phenotyped a group of 23 phylogenetically distant inbred strains for susceptibility to infection as measured by extent of fungal replication in the kidney 48 hours following infection. Susceptibility was strongly associated with the loss-of-function mutant complement component 5 (C5/Hc) allele, which is known to be inherited by approximately 40% of inbred strains. Our survey identified 2 discordant strains, AKR/J (C5-deficient, resistant) and SM/J (C5-sufficient, susceptible), suggesting that additional genetic effects may control response to systemic candidiasis in these strains. Haplotype association mapping in the 23 strains using high density SNP maps revealed several putative loci regulating the extent of C. albicans replication, amongst which the most significant were C5 (P value = 2.43×10(-11)) and a novel effect on distal chromosome 11 (P value = 7.63×10(-9)). Compared to other C5-deficient strains, infected AKR/J strain displays a reduced fungal burden in the brain, heart and kidney, and increased survival, concomitant with uniquely high levels of serum IFNγ. C5-independent genetic effects were further investigated by linkage analysis in an [A/JxAKR/J]F2 cross (n = 158) where the mutant Hc allele is fixed. These studies identified a chromosome 11 locus (Carg4, Candida albicans resistance gene 4; LOD = 4.59), and a chromosome 8 locus (Carg3; LOD = 3.95), both initially detected by haplotype association mapping. Alleles at both loci were inherited in a co-dominant manner. Our results verify the important effect of C5-deficiency in inbred mouse strains, and further identify two novel loci, Carg3 and Carg4, which regulate resistance to C. albicans infection in a C5-independent manner.

The zinc cluster transcription factor Ahr1p directs Mcm1p regulation of Candida albicans adhesion

Biofilm development by Candida albicans requires cell adhesion for the initial establishment of the biofilm and the continued stability after hyphal development occurs; however, the regulation of the process has not been fully established. Using chromatin immunoprecipitation coupled to microarray analysis (ChIP-chip) we have characterized a regulon containing the Mcm1p factor that is required for the initial surface adhesion during biofilm formation. In the yeast Saccharomyces cerevisiae several Mcm1p regulons have been characterized in which regulatory specificity is achieved through cofactors binding a sequence adjacent to the Mcm1p binding site. This new Mcm1p regulon in C. albicans also requires a cofactor, which we identify as the transcription factor Ahr1p. However, in contrast to the other yeast regulons, Ahr1p alone binds the target promoters, which include several key adhesion genes, and recruits Mcm1p to these sites. Through transcription profiling and qPCR analysis, we demonstrate that this Ahr1p-Mcm1p complex directly activates these adhesion genes. When the regulatory circuit was disrupted by deleting AHR1, the strain displayed reduced adherence to a polystyrene surface. We also demonstrate a role for the regulon in hyphal growth and in virulence. Our work thus establishes a new mechanism of Mcm1p-directed regulation distinct from those observed for other Mcm1p co-regulators.

High-level recombinant protein production in CHO cells using lentiviral vectors and the cumate gene-switch

Fast and efficient production of recombinant proteins for structural and functional studies is a crucial issue for research and for industry. To this end, we have developed an efficient system to generate in less than 2 months, starting from the cDNA, pools of CHO cells stably expressing high-level of recombinant proteins. It is based on lentiviral vectors (LVs) for stable transduction coupled with the cumate gene-switch for inducible and efficient gene expression. Transcription is initiated upon binding of the cumate transactivator (cTA) or the reverse cTA (rcTA) to the CR5 promoter. Binding of cTA or rcTA is prevented or induced by addition of cumate respectively. We first validated the CHO/LV production system with an LV carrying the secreted alkaline phosphatase (SEAP), whose expression was linked to the green fluorescent protein (GFP) through an internal ribosome entry site (IRES). CHO cells stably expressing the cTA (CHO-cTA) were transduced at various multiplicity of infection (MOI). Pools of cells were incubated at 37 and 30 degrees C during 10 days. Optimal SEAP production (65 microg/mL) was achieved at 30 degrees C with a MOI of 200. The pool stability was demonstrated for 48 days of culture by GFP expression analysis. The system was also evaluated using LV expressing three typical therapeutic proteins (a protein made up of the extracellular domain of CD200 fused to IgG Fc region [CD200Fc], a chimeric antibody [chB43], and erythropoietin [EPO]). CHO cells expressing rcTA (CHO-Cum2) were transduced with these LVs at a MOI of 200 and production was tested at 30 degrees C. After 13 days of culture, 235, 160, and 206 microg/mL of CD200Fc, chB43, and EPO were produced, respectively. The ON/OFF ratio of these pools was equal to 6 for CD200Fc, 16 for chB43, and 74 for EPO. In conclusion, this system should be very useful to produce mg quantities of recombinant proteins in a timely manner in serum free suspension culture of CHO cells for preclinical studies.

Cysteamine, the natural metabolite of pantetheinase, shows specific activity against Plasmodium

In mice, loss of pantetheinase activity causes susceptibility to infection with Plasmodium chabaudi AS. Treatment of mice with the pantetheinase metabolite cysteamine reduces blood-stage replication of P. chabaudi and significantly increases survival. Similarly, a short exposure of Plasmodium to cysteamine ex vivo is sufficient to suppress parasite infectivity in vivo. This effect of cysteamine is specific and not observed with a related thiol (dimercaptosuccinic acid) or with the pantethine precursor of cysteamine. Also, cysteamine does not protect against infection with the parasite Trypanosoma cruzi or the fungal pathogen Candida albicans, suggesting cysteamine acts directly against the parasite and does not modulate host inflammatory response. Cysteamine exposure also blocks replication of P. falciparum in vitro; moreover, these treated parasites show higher levels of intact hemoglobin. This study highlights the in vivo action of cysteamine against Plasmodium and provides further evidence for the involvement of pantetheinase in host response to this infection.

Reverse genetics in Candida albicans predicts ARF cycling is essential for drug resistance and virulence

Candida albicans, the major fungal pathogen of humans, causes life-threatening infections in immunocompromised individuals. Due to limited available therapy options, this can frequently lead to therapy failure and emergence of drug resistance. To improve current treatment strategies, we have combined comprehensive chemical-genomic screening in Saccharomyces cerevisiae and validation in C. albicans with the goal of identifying compounds that can couple with the fungistatic drug fluconazole to make it fungicidal. Among the genes identified in the yeast screen, we found that only AGE3, which codes for an ADP-ribosylation factor GTPase activating effector protein, abrogates fluconazole tolerance in C. albicans. The age3 mutant was more sensitive to other sterols and cell wall inhibitors, including caspofungin. The deletion of AGE3 in drug resistant clinical isolates and in constitutively active calcineurin signaling mutants restored fluconazole sensitivity. We confirmed chemically the AGE3-dependent drug sensitivity by showing a potent fungicidal synergy between fluconazole and brefeldin A (an inhibitor of the guanine nucleotide exchange factor for ADP ribosylation factors) in wild type C. albicans as well as in drug resistant clinical isolates. Addition of calcineurin inhibitors to the fluconazole/brefeldin A combination only initially improved pathogen killing. Brefeldin A synergized with different drugs in non-albicans Candida species as well as Aspergillus fumigatus. Microarray studies showed that core transcriptional responses to two different drug classes are not significantly altered in age3 mutants. The therapeutic potential of inhibiting ARF activities was demonstrated by in vivo studies that showed age3 mutants are avirulent in wild type mice, attenuated in virulence in immunocompromised mice and that fluconazole treatment was significantly more efficacious when ARF signaling was genetically compromised. This work describes a new, widely conserved, broad-spectrum mechanism involved in fungal drug resistance and virulence and offers a potential route for single or improved combination therapies.

Candida albicans is a fungus that normally resides as part of the microflora in the human gut. Candida species can cause superficial infections like thrush in the healthy human population and life-threatening invasive infections in immunocompromised patients. Fungal infections are often treated with azole drugs, but due to the fungistatic nature of these agents, C. albicans can develop drug resistance, leading to therapy failure. To improve the action of azoles and convert them into fungicidal drugs, we first systematically analyzed the genetic requirements for tolerance to one such azole drug, fluconazole. We show, both genetically and pharmacologically, that components of the ARF cycling machinery are critical in mediating both azole and echinocandin tolerance in C. albicans as well as several other pathogenic Candida species and in the pathogenic mold Aspergillus fumigatus. We highlight the importance of ARF cycling in drug resistance by showing that genetic compromise of ARF functions overrides common drug resistance mechanisms in clinical samples and other key regulators of azole/echinocandin tolerance. We validated the therapeutic potential of ARF cycling in two mouse models and provide evidence that drug treatment is more efficacious when ARF activities are genetically compromised. Our study demonstrates a new mechanism involved in two important aspects of the biology of human fungal pathogens and provides a potential route for improved antifungal therapies.

Forward genetics in Candida albicans that reveals the Arp2/3 complex is required for hyphal formation, but not endocytosis

Candida albicans is a diploid fungal pathogen lacking a defined complete sexual cycle, and thus has been refractory to standard forward genetic analysis. Instead, transcription profiling and reverse genetic strategies based on Saccharomyces cerevisiae have typically been used to link genes to functions. To overcome restrictions inherent in such indirect approaches, we have investigated a forward genetic mutagenesis strategy based on the UAU1 technology. We screened 4700 random insertion mutants for defects in hyphal development and linked two new genes (ARP2 and VPS52) to hyphal growth. Deleting ARP2 abolished hyphal formation, generated round and swollen yeast phase cells, disrupted cortical actin patches and blocked virulence in mice. The mutants also showed a global lack of induction of hyphae-specific genes upon the yeast-to-hyphae switch. Surprisingly, both arp2 Delta/Delta and arp2 Delta/Delta arp3 Delta/Delta mutants were still able to endocytose FM4-64 and Lucifer Yellow, although as shown by time-lapse movies internalization of FM4-64 was somewhat delayed in mutant cells. Thus the non-essential role of the Arp2/3 complex discovered by forward genetic screening in C. albicans showed that uptake of membrane components from the plasma membrane to vacuolar structures is not dependent on this actin nucleating machinery.

Transcriptional regulation of carbohydrate metabolism in the human pathogen Candida albicans

Glycolysis is a metabolic pathway that is central to the assimilation of carbon for either respiration or fermentation and therefore is critical for the growth of all organisms. Consequently, glycolytic transcriptional regulation is important for the metabolic flexibility of pathogens in their attempts to colonize diverse niches. We investigated the transcriptional control of carbohydrate metabolism in the human fungal pathogen Candida albicans and identified two factors, Tye7p and Gal4p, as key regulators of glycolysis. When respiration was inhibited or oxygen was limited, a gal4tye7 C. albicans strain showed a severe growth defect when cultured on glucose, fructose or mannose as carbon sources. The gal4tye7 strain displayed attenuated virulence in both Galleria and mouse models as well, supporting the connection between pathogenicity and metabolism. Chromatin immunoprecipitation coupled with microarray analysis (ChIP-CHIP) and transcription profiling revealed that Tye7p bound the promoter sequences of the glycolytic genes and activated their expression during growth on either fermentable or non-fermentable carbon sources. Gal4p also bound the glycolytic promoter sequences and activated the genes although to a lesser extent than Tye7p. Intriguingly, binding and activation by Gal4p was carbon source-dependent and much stronger during growth on media containing fermentable sugars than on glycerol. Furthermore, Tye7p and Gal4p were responsible for the complete induction of the glycolytic genes under hypoxic growth conditions. Tye7p and Gal4p also regulated unique sets of carbohydrate metabolic genes; Tye7p bound and activated genes involved in trehalose, glycogen, and glycerol metabolism, while Gal4p regulated the pyruvate dehydrogenase complex. This suggests that Tye7p represents the key transcriptional regulator of carbohydrate metabolism in C. albicans and Gal4p provides a carbon source-dependent fine-tuning of gene expression while regulating the metabolic flux between respiration and fermentation pathways.

Pathogens must be able to assimilate the carbon sources in their environment to generate sufficient energy and metabolites to survive. Since glycolysis is a central metabolic pathway, it is important for this metabolic flexibility. The most commonly isolated agent in human fungal infections, Candida albicans, depends upon glycolysis for the progression of systemic disease. We investigated glycolytic transcriptional regulation in C. albicans and defined two key regulators of the pathway, Tye7p and Gal4p. We demonstrated that these factors are important for the fermentative growth of C. albicans both in vitro and in vivo and also regulate the input and output fluxes of glycolysis. The gal4tye7 strain showed attenuated virulence in a Galleria and two mouse models, potentially due to the severe growth defect in oxygen-limiting environments. Gal4p and Tye7p represent fungal specific regulators involved in the pathogenicity of the organism that may be exploited in the development of antifungal treatments. Our study describes a fungal glycolytic transcriptional circuit that is fundamentally different from that of the model yeast Saccharomyces cerevisiae, providing further evidence that the transcriptional networks in S. cerevisiae need not be generally representative of the fungal kingdom.

High-Level Recombinant Protein Production in CHO Cells Using an Adenoviral Vector and the Cumate Gene-Switch

To facilitate and accelerate the production of eukaryotic proteins with correct post-translational modifications, we have developed a protein production system based on the transduction of Chinese hamster ovary (CHO) cells using adenovirus vectors (AdVs). We have engineered a CHO cell line (CHO-cTA) that stably expresses the transactivator (cTA) of our newly developed cumate gene-switch transcription system. This cell line is adapted to suspension culture and can grow in serum-free and protein-free medium. To increase the transduction level of AdVs, we have also generated a cell line (CHO-cTA-CAR) that expresses additional amounts of the coxackievirus and adenovirus receptor (CAR) on its surface. Recombinant protein production was tested using an AdV carrying the secreted alkaline phosphatase (SEAP) under the control of the CR5 promoter, which is strongly and specifically activated by binding to cTA. The SEAP expression was linked to the expression of the green fluorescent protein (GFP) through an internal ribosome entry site (IRES) to facilitate titration of the AdV. We monitored SEAP expression on a daily basis for 9 days after transduction of CHO-cTA and CHO-cTA-CAR using different quantities of AdVs at 37 and 30 degrees C. Incubation at the latter temperature increased the production of SEAP at least 10-fold, and the presence of CAR increased the transduction level of the AdV. Maximum SEAP production (63 mg/L) was achieved at 6-7 days post-infection at 30 degrees C by transducing CHO-cTA-CAR with 500 infectious particles/cell. Because numerous AdVs can now be generated within a few weeks and large-scale production of AdVs is now a routine procedure, this system could be used to produce rapidly milligram quantities of a battery of recombinant proteins as well as for large-scale protein production.

The cumate gene-switch: a system for regulated expression in mammalian cells

Background

A number of expression systems have been developed where transgene expression can be regulated. They all have specific characteristics making them more suitable for certain applications than for others. Since some applications require the regulation of several genes, there is a need for a variety of independent yet compatible systems.

Results

We have used the regulatory mechanisms of bacterial operons (cmt and cym) to regulate gene expression in mammalian cells using three different strategies. In the repressor configuration, regulation is mediated by the binding of the repressor (CymR) to the operator site (CuO), placed downstream of a strong constitutive promoter. Addition of cumate, a small molecule, relieves the repression. In the transactivator configuration, a chimaeric transactivator (cTA) protein, formed by the fusion of CymR with the activation domain of VP16, is able to activate transcription when bound to multiple copies of CuO, placed upstream of the CMV minimal promoter. Cumate addition abrogates DNA binding and therefore transactivation by cTA. Finally, an adenoviral library of cTA mutants was screened to identify a reverse cumate activator (rcTA), which activates transcription in the presence rather than the absence of cumate.

Conclusion

We report the generation of a new versatile inducible expression system.

Bestowing inducibility on the cloned methanol dehydrogenase promoter (PmxaF) of Methylobacterium extorquens by applying regulatory elements of Pseudomonas putida F1

PmxaF is a strong methanol-inducible promoter in Methylobacterium extorquens. When this promoter is cloned in expression vectors and used to drive heterologous gene expression, methanol inducibility is either greatly reduced or entirely lost. In order to bestow inducibility upon the cloned PmxaF promoter in expression vectors, we adopted combinational methods (regulatory elements of the Pseudomonas putida F1 cym and cmt operons and Tn7 transposon system) to control reporter gene expression at the transcriptional level in M. extorquens. An operator fragment (26 nucleotides) of the cmt operon was inserted downstream of the cloned PmxaF promoter in the broad-host-range expression vector (pCHOI3). The repressor gene (cymR) located upstream of the cym operon in P. putida F1 was amplified by PCR. To avoid cellular toxicity for M. extorquens caused by the overexpression of CymR, single and/or double copies of cymR were integrated into the chromosome of M. extorquens using the mini-Tn7 transposon system. Cultures containing the chromosomally integrated cymR gene were subsequently transformed with pCHOI3 containing modified PmxaF (i.e., PmxaF plus operator). In this construct, inducibility is afforded by cumate (p-isopropylbenzoate). In this report, we describe the inducible and tightly regulated expression of heterologous genes (bgl [for beta-galactosidase], est [for esterase], and gfp [for green fluorescent protein]) in M. extorquens. This is the first documented example of an inducible/regulated heterologous gene expression system in M. extorquens.

Cardiac failure in C5-deficient A/J mice after Candida albicans infection

The effect of a deficiency in the C5 component of complement on the pathophyisology of infection with the fungal pathogen Candida albicans was studied by using the A/J inbred mouse strain and the BcA17 congenic mouse strain. Acute infection caused by intravenous injection of C. albicans blastospores is associated with rapid fungal replication in the heart, brain, and, in particular, kidneys of C5-deficient mice. Histological studies and analysis of markers for tissue damage indicated that the heart is the organ that is most affected and that it ultimately fails in C5-deficient mice. In A/J and BcA17 mice, tissue damage is associated with (i) cellular infiltration in the heart, which is not seen in the kidney despite the higher fungal load in the latter organ, and (ii) a very strong inflammatory response, including elevated levels of many cytokines and chemokines. This results in cardiomyopathy, which is associated with elevated levels of creatine kinase and cardiac troponin I in the circulation. Damage to the cardiac muscle is associated with metabolic changes, including hypoglycemia, decreased lipid utilization resulting in elevated levels of cardiac triglycerides, and unproductive glucose utilization linked to a dramatic increase in the level of pyruvate dehydrogenase kinase 4 (Pdk4), a negative regulator of the pyruvate dehydrogenase complex.

Adenovirus-Delivered Antisense RNA and shRNA Exhibit Different Silencing Efficiencies for the Endogenous Transforming Growth Factor-β(TGF-β) Type II Receptor

Gene silencing is an essential tool in gene discovery and gene therapy. Traditionally, viral delivery of antisense RNA and, more recently, small interfering RNA (siRNA) molecules in the form of small hairpin RNAs (shRNA) has been used as a strategy to achieve gene silencing. Nevertheless, the enduring challenge is to identify molecules that specifically and optimally silence a given target gene. In this study, we tested a set of adenovirus-delivered antisense RNA fragments and adenovirus-delivered shRNA molecules for their ability to target human transforming growth factor-beta type II receptor (TGFbetaRII). We used a dicistronic reporter, consisting of the coding sequences for TGFbetaRII and green fluorescent protein (GFP) to screen for optimal silencing agents targeting TGFbetaRII. Our results show, for both antisense RNA and shRNA molecules, that their effectiveness in the GFP screen correlated directly with their ability to reduce exogenously expressed TGFbetaRII. Unexpectedly, the antisense RNAs were unable to silence endogenous TGFbetaRII. In contrast, the shRNAs were able to silence endogenous TGFbetaRII. The shRNA that demonstrated the most pronounced effect on the dicistronic TGFbetaRII/GFP reporter reduced endogenous TGFbetaRII protein expression by 70% in A549 cells and reduced TGFbeta signaling by >80% in HeLa cells.

Genetic control of susceptibility to Candida albicans in susceptible A/J and resistant C57BL/6J mice

The importance of host factors in determining susceptibility to systemic Candida albicans infections is evident in both humans and mice. We have used a mouse model to study the genetic basis of susceptibility, using the inbred strains A/J and C57BL/6J, which are susceptible and resistant, respectively, based on different parameters of the response to infection. To identify genes responsible for this differential host response, brain and kidney fungal load were measured in 128 [A/J x C57BL/6J] F(2) mice 48 h after infection with 5 x 10(4) C. albicans blastospores. Segregation analysis in this informative population identified complement component 5 (C5/Hc) as the major gene responsible for this differential susceptibility (LOD of 22.7 for kidney, 19.0 for brain), with a naturally occurring mutation that causes C5 deficiency leading to enhanced susceptibility. C5 was also found to control heart fungal load, survival time, and serum TNF-alpha levels during infection. Investigation of the response to C. albicans challenge in a series of AcB/BcA recombinant congenic strains validated the importance of C5 in determining the host response. However, the strains BcA67 and BcA72 showed discordant phenotypes with respect to their C5 status, suggesting additional complexity in the genetic control of the inter-strain difference in susceptibility observed in A/J and C57BL/6J following systemic infection with C. albicans.

A mutation in the Icsbp1 gene causes susceptibility to infection and a chronic myeloid leukemia-like syndrome in BXH-2 mice

BXH-2 mice develop a fatal myeloid leukemia by a two-step mutagenic process. First, a BXH-2-specific recessive mutation causes a myeloproliferative syndrome. Second, retroviral insertions alter oncogenes or tumor suppressors, resulting in clonal expansion of leukemic cells. We have identified a recessive locus on chromosome 8 (Myls) that is responsible for myeloproliferation in BXH-2. This Myls interval has been narrowed down to 2 Mb and found to contain several positional candidates, including the interferon consensus sequence-binding protein 1 gene (Icsbp, also known as interferon regulatory factor 8 [IRF8]). We show that BXH-2 mice carry a mutation (915 C to T) resulting in an arginine-to-cysteine substitution at position 294 within the predicted IRF association domain of the protein. Although expression of Icsbp1 mRNA transcripts is normal in BXH-2 splenocytes, these cells are unable to produce interleukin 12 and interferon-gamma in response to activating stimuli, confirming that R294C behaves as a loss-of-function mutation. Myeloproliferation in BXH-2 mice is concomitant to increased susceptibility to Mycobacterium bovis (BCG) despite the presence of resistance alleles at the Nramp1 locus. These results suggest a two-step model for chronic myeloid leukemia in BXH-2, in which inactivation of Icsbp1 predisposes to myeloproliferation and immunodeficiency. This event is required for retroviral replication, and subsequent insertional mutagenesis that causes leukemia in BXH-2 mice.

Genetic analysis of innate immunity in resistance to Candida albicans

Systemic candidiasis is a significant cause of nosocomial infections and the mechanisms of defense against Candida albicans in humans remain poorly understood. Studies in animal models have demonstrated the importance of innate immunity in controlling the response to infection. Although Th1 cytokines have been shown to direct the overall outcome of infection, the precise role of the Th1/Th2 response and, more generally, the adaptive immune response as a whole, in systemic candidiasis, appears to apply mainly to the development of resistance to reinfection. A genetic approach to the identification of host factors regulating pathogenesis and susceptibility to C. albicans infection has been used in humans and in mouse models of infection. Mouse mutants bearing experimentally induced mutations in specific genes have provided a systematic tool for directly assessing the role of individual proteins in C. albicans susceptibility. Inbred mouse strains have been valuable in showcasing the spectrum of naturally occurring variations in initial susceptibility to infection, and type of disease developed. Crosses between resistant and susceptible strains have led to the detection of additional gene effects affecting innate immunity. Of particular interest is the major effect of a naturally occurring loss-of-function mutation in the C5 complement component that has become fixed in many inbred strains. These and other studies have shown that both a functional complement pathway and robust inflammatory response are critical for resistance to C. albicans.

Dysregulated inflammatory response to Candida albicans in a C5-deficient mouse strain

Experimental infection of inbred mouse strains with Candida albicans provides a good model system to identify host genetic determinants that regulate onset of, response to, and ultimate outcome of disseminated candidiasis. The A/J mouse strain is exquisitely sensitive to infection with C. albicans, while the C57BL/6J strain is relatively resistant, as measured by survival following intravenous injection of Candida blastospores. This differential susceptibility is caused by an A/J-specific loss-of-function mutation in the C5 component of the complement pathway. C5 plays several critical roles in host response to infection, including target lysis and phagocyte recruitment. Therefore, to determine which of its functions were required for host resistance to candidiasis, a detailed comparative analysis of pathophysiology and host response to acute C. albicans infection was conducted in A/J and C57BL/6J mice. C5-sufficient C57BL/6J mice were found to succumb late in infection due to severe kidney pathology, typified by fungal replication and robust neutrophil-based inflammatory response associated with extensive tissue damage. In contrast, A/J mice were moribund within 24 h postinfection but displayed little if any kidney damage despite an inability to mobilize granulocytes and a high fungal load in the kidney. Rather, C5 deficiency in A/J mice was associated with higher levels of circulating cytokines tumor necrosis factor alpha, interleukin-6, monocyte chemotactic protein 1 (MCP-1), MCP-5, and eotaxin in response to C. albicans. Transfer of the C5-defective allele from A/J onto a C57BL/6J genetic background in recombinant congenic strain BcA17 recapitulated the phenotypic aspects of the susceptibility of A/J mice to C. albicans, confirming the causative role of C5 deficiency in the dysregulated cytokine response.

Gene expression in HL60 granulocytoids and human polymorphonuclear leukocytes exposed to Candida albicans

Candida albicans is an opportunistic human pathogen causing both superficial and disseminated diseases. It is a dimorphic fungus, switching between yeast and hyphal forms, depending on cues from its microenvironment. Hyphae play an important role in the pathogenesis of candidiasis. The host's response to Candida infection is multifaceted and includes the participation of granulocytes as key effector cells. The aim of this investigation was to study host gene expression during granulocyte-Candida interaction. Effector cells were generated by the granulocytic differentiation of HL60 cells. The resulting cell population was shown to be morphologically and functionally equivalent to granulocytes and is therefore referred to as HL60 granulocytoids for the purposes of this study. Gene expression profiles were determined 1 h after hosts were infected with C. albicans. Three Candida-granulocytoid ratios were chosen to reflect different degrees of HL60 granulocytoid inhibition of C. albicans. The data demonstrate that at the high pathogen-host ratio, C. albicans modulated the HL60 granulocytoid's response by downregulating the expression of known antimicrobial genes. In addition, looking at the expression of a large number of genes, not all of which have necessarily been implicated in candidastatic or candidacidal mechanisms, it has been possible to describe the physiological response of the HL60 granulocytoid to an infectious challenge with C. albicans. Finally, some of the observed changes in HL60 granulocytoid gene expression were investigated in freshly isolated human polymorphonuclear leukocytes infected with C. albicans. Similar changes were seen in these primary human cells, lending support to the validity of this model.

Expanded bed adsorption of human serum albumin from very dense Saccharomyces cerevesiae suspensions on fluoride-modified zirconia

The adsorption of proteins from high cell density yeast suspensions on mixed-mode fluoride-modified zirconia (FmZr) particles (38 to 75 microm, surface area of 29 m(2)/g and density of 2.8 g/cm(3)) was investigated using human serum albumin (HSA) added to Saccharomyces cerevesiae as the model expression host. Because of the high density of the porous zirconia particles, HSA (4 mg/mL) can be adsorbed from a 100 g dry cell weight (DCW)/L yeast suspension in a threefold-expanded bed of FmZr. The expanded bed adsorption of any protein from a suspension containing >50 g DCW/L cells has not been previously reported. The FmZr bed expansion characteristics were well represented by the Richardson-Zaki correlation with a particle terminal velocity of 3.1 mm/s and a bed expansion index of 5.4. Expanded bed hydrodynamics were investigated as a function of bed expansion using residence time distribution studies with sodium nitrite as the tracer. The adsorption of HSA on FmZr exhibited features of multicomponent adsorption due to the presence of dimers. The protein binding capacity at 5% breakthrough decreased from 22 mg HSA/mL settled bed void volume for 20 g DCW/L yeast to 15 mg HSA/mL settled bed void volume for 40 g DCW/L yeast and remained unchanged for the higher yeast concentrations (60 to 100 g DCW/L). However, the batch (or equilibrium) binding capacity decreased monotonically as a function of yeast concentration (20 to 100 g DCW/L) and the binding capacity at 100 g DCW/L yeast was fivefold lower compared with that at 20 g DCW/L yeast. The lower batch binding capacity at high cell concentrations resulted from the adsorption of cells at the surface of the particles restricting access of HSA to the intraparticle surface area. Batch (or equilibrium) and column HSA adsorption results indicated that the adsorption of HSA on FmZr occurred at a time scale that may be much faster than that of yeast cells. The zirconia particles were cleaned of adsorbed HSA and yeast with a total of 1500 to 2000 column volumes (over many cycles) of 0. 25 M NaOH, without any significant effect on the chromatographic performance.

Physical delineation of a 700-kb region overlapping the Looptail mutation on mouse chromosome 1

The mouse looptail (Lp) mutation is an established model for neural tube defects with homozygous Lp embryos showing an open neural tube from the caudal midbrain to the tip of the tail. Heterozygous Lp mice are characterized by a "looped-tail" and wobbly head movements. The Lp gene has been mapped to a 0.6-cM interval on mouse chromosome 1 delineated by two clusters of markers, Fcer1gamma/Usf1/D1Mit113/D1Wsu1 on the proximal side and Fcer1alpha/Spna1/D1Mit149 distally. In the present study, we have created a high-resolution physical map of the Lp genetic interval that is based on long-range restriction mapping by PFGE, fluorescence in situ hybridization analysis of interphase nuclei and extended chromatid fibers, and the assembly of a cloned contig. This contig consists of 25 independent and overlapping BAC clones and 3 YAC clones. The combined analysis indicates that the 0.6-cM genetic interval for Lp corresponds to a minimal physical interval of 700 kb that is delineated by D1Mit113 proximally (two crossovers) and Fcer1alpha distally (one crossover). The overall gene order and intergene distances for the region were determined to be D1Mit113-<150 kb-Nhlh1-250 kb-Atp1alpha2-280 kb-Fcer1alpha. Partial sequencing of BAC clones from the contig yielded 42 new STS markers for this region of mouse chromosome 1. Sequence analysis of the BAC clones and assignment of ESTs from the human transcript map to the cloned contig allowed the placement of four new transcription units within this region: Pc326, Kiaa0253, and Pea15 were positioned in the Nhlh1/Atp1alpha2 nonrecombinant interval, while Girk3 was located distal to Atp1alpha2.

Wild-type egr1/Krox24 promotes and dominant-negative mutants inhibit, pluripotent differentiation of p19 embryonal carcinoma cells

The zinc-finger transcription factor Krox24 was analysed for its role in differentiation in P19 embryonal carcinoma cells. Reciprocal dominant negative mutants consisting of Krox24 deleted for a crucial region of the zinc-finger domain (delta Krox24) or of the zinc-finger region alone (delta Krox24Zf) abolished the activation of transcription by Krox24 in P19 cells. Expression of Krox24 led to spontaneous differentiation of P19 cells in a lineage-independent fashion. Krox24 transfected populations, as well as individual clones randomly picked from them, displayed a wide array of diverse morphologies and expressed markers characteristic of a variety of differentiated cells. The dominant negative mutants blocked differentiation of P19 cells. We conclude that expression of Krox24 is sufficient for pluripotent differentiation of embryonal carcinoma cells, and that expression of Krox24 or other egr family members is essential to this process.

Expanded and packed bed albumin adsorption on fluoride modified zirconia

The expanded bed characteristics of 75-103microm fluoride-modified zirconia (FmZr) particles synthesized by a fed batch oil emulsion process were investigated. These particles are distinguished from commercially available expanded-bed adsorbents by virtue of their high density (2.8 g/cc) and the mixed mode protein retention mechanism which allows for the retention of both cationic and anionic proteins. The linear velocity versus bed porosity data agree with the Richardson-Zaki relationship with the terminal velocity in infinite medium of 2858.4 cm/h and a bed expansion index of 5.1. Residence time distribution (RTD) studies and bovine serum albumin (BSA) adsorption studies were performed as a function of the height of the settled bed to the column diameter (H:D) ratio and degree of bed expansion with superficial velocities of 440 to 870 cm/h. The settled bed, a 2x expanded bed, and a 3x expanded bed were studied for the H:D ratios of 1:1, 2:1, and 3:1. The dynamic binding capacity (DBC) at 5% breakthrough was low (2-8 mg BSA/mL settled bed) and was independent of the H:D ratio or the degree of bed expansion. The saturation DBC was 32.3 +/- 7.0 mg BSA/mL settled bed. The adsorption-desorption kinetics and intraparticle diffusion for protein adsorption on FmZr (38-75 micrometer) were investigated by studying the packed bed RTD and BSA adsorption as a function of temperature and flow rate. The data show that the adsorption-desorption kinetics along with intraparticle diffusion significantly influence protein adsorption on FmZr. Low residence times ( approximately 0.8 min) of BSA result in a DBC at 5% breakthrough which is 3.5-fold lower compared to that at 6-fold higher protein residence time. At low linear velocity (45 cm/h) the breakthrough curve is nearly symmetrical and becomes asymmetrical and more dispersed at higher linear velocity (270 cm/h) due to the influence of slow adsorption-desorption kinetics and intraparticle diffusion. Bioeng 60: 333-340, 1998.

Comparison of fluoride modified zirconia with ceramic hydroxyapatite for preparative scale purification of immunoglobulin from serum albumin

The utility of 50 microns fluoride modified zirconia particles as an easily cleaned and steam sterilizable low pressure preparative scale stationary phase for immunoglobulin purification was investigated and its performance was compared with 40 microns ceramic hydroxyapatite type II (cHAp II) particles. The equilibrium batch binding capacity of both supports for bovine serum albumin decreases monotonically with increase in the adsorption pH, while that for bovine IgG is independent of pH, in the pH ranges studied. The dynamic binding capacity, as determined by breakthrough analysis, was 29 mg BSA/g zirconia for fluoride modified zirconia and 8.6 mg BSA/g cHAp II for cHAp II. Linear gradient conditions were developed for the separation of BSA and IgG on fluoride modified zirconia. The same separation could be accomplished in a shorter time and with better resolution on cHAp II.

Antagonism between Nur77 and glucocorticoid receptor for control of transcription

Two important functions of glucocorticoids (Gc), namely, suppression of immune system function and feedback repression of the hypothalamo-pituitary-adrenal (HPA) axis, are mediated through repression of gene transcription. Previous studies have indicated that this repression is exerted in part through antagonism between the glucocorticoid receptors (GR) and the AP-1 family of transcription factors. However, this mechanism could not account for repression of the pro-opiomelanocortin (POMC) gene, an important regulator of the HPA axis. Our recent identification of the orphan nuclear receptor Nur77 as a mediator of CRH induction of POMC transcription led us, in the present work, to show that Gc antagonize this positive signal at two levels. First, Gc partly blunt the CRH induction of Nur77 mRNA, and second, they antagonize Nur77-dependent transcription. GR repression is exerted by antagonism of Nur77 action on the NurRE element of the POMC gene. Gc antagonism of NurRE activity was observed in response to physiological stimuli in both endocrine (CRH induction of POMC) and lymphoid (T-cell receptor activation) cells. In transfection experiments, transcriptional activation by Nur77 and the repressor activity of liganded GR titrated each other on their cognate DNA target. In vitro binding experiments as well as mutation analysis of GR suggest that the mechanism of GR antagonism of Nur77 is very similar to that of the antagonism between GR and AP-1. The convergence of positive signals mediated by Nur77 (and also probably by related family members) and negative signals exerted by GR appears to be a general mechanism for control of transcription, since it is active in both endocrine and lymphoid cells.

Nhlh1, a basic helix-loop-helix transcription factor, is very tightly linked to the mouse looptail (Lp) mutation

Looptail (Lp) is a mutation on the distal portion of mouse Chromosome (Chr) 1 that affects neurulation in mouse and is phenotypically expressed by appearance of an open neural tube along the entire antero-posterior axis of the embryo (craniorachischisis). Nhlh1, a member of the basic helix-loop-helix family of transcription factors, is expressed in the developing neural tube in structures affected by the Lp mutation and has been regionally assigned to the distal part of mouse Chr 1. Using a large panel of looptail animals from an (Lp/+ x SWR/J)F1 x SWR/J segregating backcross progeny, we have determined that Nhlh1 maps very close to Lp, with no recombinant detected in 500 informative animals tested; both map within a 0.6-cM segment defined as D1Mit113/Apoa2/Fcer1 gamma-(0.4 cM)-Nhlh1/Lp-(0.2 cM)-Fcer1 alpha/D1Mit149/Spna1. Nucleotide sequencing of Nhlh1 cDNA clones from wild type (WT) and Lp/Lp embryos failed to identify sequence alterations associated with the mutant phenotype. Southern hybridization of genomic DNA from WT and Lp/Lp embryos failed to identify specific rearrangements at or near the Nhlh1 locus, and Northern RNA blotting and RT-PCR evaluation of Nhlh1 mRNA expression indicated that both the levels and types of Nhlh1 mRNAs produced in WT and Lp/Lp embryos were indistinguishable. These studies suggest that Nhlh1 and Lp are not allelic. Nevertheless, Nhlh1 is the Chr 1 marker most tightly linked to Lp identified to date and can, therefore, be used as an excellent entry probe to clone the Lp region.

High-resolution linkage map in the vicinity of the Lp locus

Looptail (Lp) is a mutation that profoundly affects neurulation in mouse and is characterized by craniorachischisis, an open neural tube extending from the midbrain to the tail in embryos homozygous for the mutation. Lp maps to the distal portion of mouse chromosome 1, and as part of a positional cloning approach, we have generated a high-resolution linkage map of the Lp chromosomal region. For this, we have carried out extensive segregation analysis in a total of 706 backcross mice informative for Lp and derived from two crosses, (Lp/+ x SJL/J)F1 x SJL/J and (Lp/+ x SWR/J) F1 x SWR/J. In addition, 269 mice from a (Mus spretus x C57BL/6J)F1 x C57BL/6J interspecific backcross were also used to order marker loci and calculate intergene distances for this region. With these mice, a total of 28 DNA markers corresponding to either cloned genes or anonymous markers of the SSLP or SSCP-types were mapped within a 5-cM interval overlapping the Lp region, with the following locus order and interlocus distances (in cM): centromere--D1Mit110/Atp1 beta 1/Cd3 zeta/Cd3 eta/D1Mit145-D1Hun14/D1Mit15- D1Mit111/D1Mit112-D1Mit114-D1Mit148/D1Mit205+ ++/D1Mit36/D1Mit146/D1Mit147/D1Mit270 / D1Hun13-Fcgr2-Mpp-Apoa2/Fcer1 gamma-Lp-D1Mit149/Spna1/Fcer1 alpha-Eph1-Hlix1/D1Mit62. These studies have allowed the delineation of a maximum genetic interval for Lp of 0.5 cM, a size amenable to physical mapping techniques.

Characterization of the estrogen receptor in two antiestrogen-resistant cell lines, LY2 and T47D

Drug resistance occurs frequently during breast cancer treatment with antiestrogens. Since antiestrogen action is mediated by the estrogen receptor (ER), we have examined both the structural and functional properties of the ER present in two breast cancer cell lines, LY2 and T47D, which proliferate rapidly in the presence of antiestrogens. The ER function in LY2 cells was indistinguishable from that of the parental tamoxifen-sensitive MCF-7 cells as assessed by estrogen regulation of two endogenous genes and estrogen-regulated transcription in a transient transfection system. RNase protection assays, sensitive enough to detect single base pair mismatches, showed that the sequence of the coding region of ER of LY2 and T47D cells was wild type. Thus the ER appears to be normal in two independently isolated breast cancer cell lines whose growth is resistant to the inhibitory effect of antiestrogens. Moreover by conducting the cell proliferation studies in a phenol red-free medium, we have demonstrated that the antiestrogen resistance of LY2 and T47D cells corresponds in fact to an estrogen-independent growth.

The cloned human oestrogen receptor contains a mutation which alters its hormone binding properties

We demonstrate here that the human oestrogen receptor (hER) cDNA clone pOR8 obtained from MCF-7 cells contains an artefactual point mutation which results in the substitution of a valine for a glycine at amino acid position 400 (Gly-400----Val-400). This mutation in the hormone binding domain of the cloned hER destabilizes its structure and decreases its apparent affinity for oestradiol at 25 degrees C, but not at 4 degrees C, when compared with the wild-type hER with a Gly-400.

Progesterone receptor synthesis and degradation in MCF-7 human breast cancer cells as studied by dense amino acid incorporation. Evidence for a non-hormone binding receptor precursor

We have used the technique of density labeling of proteins by biosynthetic incorporation of 2H, 13C, 15N (dense) amino acids to study the synthesis and degradation rates of the progesterone receptor in MCF-7 human breast cancer cells. In cells grown in the absence of progestin, sucrose gradient shift analyses reveal that it takes 17 h for the normal density progesterone receptor levels to be reduced to half the initial value, whereas in the presence of 10 nM of the synthetic progestin [3H]R5020, the receptor turns over more rapidly, such that the normal density R5020-occupied progesterone receptor complexes are reduced to half in 12 h. The accelerated progesterone receptor turnover in the presence of [3H]R5020 reflects increased turnover rates of both the A (Mr-85,000) and B (Mr-115,000) subunits, as determined by sodium dodecyl sulfate gel analyses of dense and light receptors photoaffinity labeled with [3H]R5020. In both control and progestin-exposed cells, the time course of progesterone receptor turnover shows a lag of approximately 6 h after dense (15N, 13C, 2H) amino acid exposure, before dense hormone binding receptor species are seen and before normal density progestin binding activity starts decreasing. Since our evaluations of progesterone receptor depend upon its binding of radiolabeled ligand ([3H]R5020), this lag in the density shift kinetics would be consistent with the presence of a non-hormone binding biosynthetic precursor, from which the hormone-binding form of progesterone receptor is derived. A kinetic model is used to analyze the lag-decay profiles and to determine the rate constants for progesterone receptor synthesis, activation to the hormone-binding form, and degradation.

Antiprogestin-receptor complexes: differences in the interaction of the antiprogestin RU38,486 and the progestin R5020 with the progesterone receptor of human breast cancer cells

In order to understand the molecular basis for antiprogestin action, we have compared the interaction of the antiprogestin [3H]RU38, 486 (RU486) and the progestin [3H]R5020 with the progesterone receptor (PR). In both MCF-7 and T47D human breast cancer cells, we have observed marked differences in the sedimentation properties of the PR on high salt sucrose gradients: while the R5020-receptor complexes sediment at approximately 4 S (4.4 +/- 0.1 S), the RU486-receptor sediments as a prominent 6 S species as well as a 4 S species. This binding is abolished by excess unlabelled R5020, RU486 or progesterone, but is unaffected by excess unlabelled hydrocortisone or dexamethasone, indicating that both the 4 S and 6 S species represent the PR and not glucocorticoid receptor. Although the relative distribution of 4 S and 6 S forms is not altered by treatment with DNAse or RNAse, exposure to 10 mM thioglycerol or to 3 M urea results in conversion of the 6 S to the 4 S form, suggesting that disulfide bonds and hydrophobic interactions are important in maintaining the integrity of the 6 S form. These findings suggest that the 6 S antiprogestin complex is formed as a result of the interaction of PR units with each other or with a different protein. This change in receptor association state may be an important aspect of the antiprogestin activity of RU486.

Antiestrogen action in breast cancer cells: modulation of proliferation and protein synthesis, and interaction with estrogen receptors and additional antiestrogen binding sites

Antiestrogens have proven to be effective in controlling the growth of hormone-responsive breast cancers. At the concentrations of antiestrogens achieved in the blood of breast cancer patients taking antiestrogens (up to 2 X 10(-6) M), antiestrogens selectively inhibit the proliferation of estrogen receptor-containing breast cancer cells, and this inhibition is reversible by estradiol. Antiestrogens also inhibit estrogen-stimulation of several specific protein synthetic activities in breast cancer cells, including increases in plasminogen activator activity, progesterone receptor levels and production of several secreted glycoproteins and intracellular proteins. Antiestrogens bind with high affinity to the estrogen receptor and to additional microsomal binding sites to which estrogens do not bind. These latter sites, called antiestrogen binding sites (AEBS), are present in equal concentrations in estrogen receptor-positive and -negative breast cancer cells and are present in a wide variety of tissues, with highest concentrations being found in the liver. The antiestrogenic and growth suppressive potencies of a variety of antiestrogens correlate best with their affinity for estrogen receptor and not with affinity for AEBS. Antiestrogens undergo bioactivation and metabolism in vivo and hydroxylated forms of the antiestrogen have markedly enhanced affinities for the estrogen receptor. Detailed studies with high affinity radiolabelled antiestrogens indicate that antiestrogens induce important conformational changes in receptor that are reflected in the enhanced maintenance of a 5 S form of the estrogen receptor complex; reduced interaction with DNA; and altered activation and dissociation kinetics of the antiestrogen-estrogen receptor complex. These conformational changes effected by antiestrogens likely result in different interactions with chromatin, causing altered cell proliferation and protein synthesis. Analyses of the rates of synthesis and turnover of the estrogen receptor through pulse-chase experiments utilizing the covalently attaching antiestrogen, tamoxifen aziridine, and studies employing dense amino acid labeling of estrogen receptor reveal that the antiestrogen-occupied receptor is degraded at a rate (t 1/2 = 4 h) similar to that of the control unoccupied receptor. Hence, antiestrogens do not prevent estrogen receptor synthesis and they do not either accelerate or block estrogen receptor degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of the subunit nature of nuclear estrogen receptors by chemical cross-linking and dense amino acid labeling

We have used chemical cross-linking and dense amino acid labeling of estrogen receptors to characterize the subunit nature and rate of turnover of nuclear 5S estrogen-receptor complexes. When MCF-7 human breast cancer cells are incubated with [3H]estradiol or [3H]antiestrogen [alpha-[4-pyrrolidinoethoxy]phenyl-4-hydroxy-alpha'-nitrostilbe ne (CI628M) or (Z)-1-[4-(2-[N-aziridinyl]ethoxy)phenyl] 1,2-diphenyl-1-butene (tamoxifen aziridine)] and nuclear estrogen-receptor complexes are extracted with 0.6 M KCl and then chemically cross-linked with the cross-linker 2-iminothiolane, the cross-linked receptor complexes sediment as a 5.4S species on 3 M urea-containing sucrose gradients, while the noncross-linked species are 4S. Sodium dodecyl sulfate-polyacrylamide gel analyses of these cross-linked nuclear receptor complexes labeled with the covalently attaching ligand [3H]tamoxifen aziridine reveal a species of about 130,000 mol wt, while the noncross-linked or the cross-linked but mercaptan-cleaved receptor is 65,000 mol wt. Both receptor species are also detectable by interaction with an immunoadsorbent column containing antireceptor monoclonal antibody. For analyses of receptor turnover rates, cells exposed for different time periods to medium containing dense (15N, 13C, and 2H) amino acids were labeled with [3H]antiestrogen [1-[4-(2-dimethylaminoethoxy)phenyl]1-[4-hydroxyphenyl] 2-phenylbut-1-(2)ene (trans-hydroxytamoxifen) or CI628M] or [3H]estradiol, and salt-extracted nuclear estrogen receptors were analyzed on sucrose gradients. The normal density 5S form shifted to a broader, more dense peak at 2 and 4 h and finally, by 8-10 h, to a more dense, sharply sedimenting species. The time course of this shift is the same as that seen for the 4S urea-dissociated nuclear receptor form (t1/2 approximately 4h), suggesting that the 5.4S nuclear receptor is composed of two species which turn over at the same rate. We conclude from these cross-linking and density shift experiments that the nuclear 5S receptor complex consists of two similarly sized units, which turn over with similar half-lives. These data provide strong evidence that the 5S nuclear receptor complex is a homodimer of two 4S, 65,000 mol wt monomers.

Estrogen receptor synthesis and turnover in MCF-7 breast cancer cells measured by a density shift technique

The level of estrogen receptor (ER) is a major factor regulating cell sensitivity to estrogen. We have determined the rates of ER synthesis and turnover in MCF-7 breast cancer cells by incubating cells in medium supplemented with 13C15N2H-amino acids (dense amino acids) and monitoring the shift from "old-light" (preexisting) to "new-dense" (newly synthesized) receptors by velocity sedimentation on 0.4-M KCl, 5-20% sucrose gradients prepared in buffered deuterium oxide. Cytosol or unoccupied nuclear ER prepared from control cells grown in the presence of 12C14N1H-amino acids (normal amino acids) and labeled in vitro with [125I]iodoestradiol sediments as a single, normal density peak. When cells were incubated in medium supplemented with dense amino acids for various periods of time, the [125I]iodoestradiol-labeled receptor showed a progressive shift with time to a denser species; by 3 h, a more rapidly sedimenting shoulder was observed on the normal density peak; by 6 h, 40% of the receptor sedimented at the normal density rate, with 60% at a more rapid rate; by 8 h, the predominant peak (70%) was at the more dense position, and at 15 h, all of the sites sedimented as the denser form. Thus, the magnitude of the receptor peak of normal density as a function of time in dense medium indicates that the receptor in control cells has a half-life of 4.0-4.5 h. To determine whether estradiol or the antiestrogens nafoxidine (U11,100A; (1-(2-[p-(3,4-dihydro-6-methoxy-2-phenyl-1-naphthyl)phenoxy] ethyl)pyrrolidine hydrochloride) or CI628 affected the turnover rate of the receptor, measurements were performed on cells grown in the continuous presence of estradiol or antiestrogen (steady state conditions). Exposure of cells to 10 nM estradiol was found to increase the turnover rate of the nuclear receptor, while exposure to 200 nM nafoxidine or CI628 (alpha-(p-[2-(1-pyrrolidino)ethoxy]phenyl)4-methoxy-alpha'- nitrostillbene) did not substantially alter the turnover rate of the nuclear receptor. The half-lives of receptor were found to be 4.02 +/- 0.23 and 4.47 +/- 0.26 h for control unoccupied cytosol and nuclear receptors, 3.00 +/- 0.38 h for estradiol-occupied nuclear receptors, 4.90 +/- 0.66 h for CI628-occupied nuclear receptors, and 3.43 +/- 0.37 h for nafoxidine-occupied nuclear receptors. These results indicate that ER turns over rapidly, with a half-life of 3-5 h, in the presence or absence of estradiol or antiestrogen, and that receptor synthesis is also rapid, with the rate of appearance of newly synthesized receptor being 0.3-0.5 pmol/mg DNA . h. These rates provide the cell with the capacity for dynamic and rapid regulation of its ER levels.