Aven and Bcl-xL enhance protection against apoptosis for mammalian cells exposed to various culture conditions

Aven-dependent activation of ATM following DNA damage

BACKGROUND

In response to DNA damage, cells undergo either cell-cycle arrest or apoptosis, depending on the extent of damage and the cell's capacity for DNA repair. Cell-cycle arrest induced by double-stranded DNA breaks depends on activation of the ataxia-telangiectasia (ATM) protein kinase, which phosphorylates cell-cycle effectors such as Chk2 and p53 to inhibit cell-cycle progression. ATM is recruited to double-stranded DNA breaks by a complex of sensor proteins, including Mre11/Rad50/Nbs1, resulting in autophosphorylation, monomerization, and activation of ATM kinase.

RESULTS

In characterizing Aven protein, a previously reported apoptotic inhibitor, we have found that Aven can function as an ATM activator to inhibit G2/M progression. Aven bound to ATM and Aven overexpressed in cycling Xenopus egg extracts prevented mitotic entry and induced phosphorylation of ATM and its substrates. Immunodepletion of endogenous Aven allowed mitotic entry even in the presence of damaged DNA, and RNAi-mediated knockdown of Aven in human cells prevented autophosphorylation of ATM at an activating site (S1981) in response to DNA damage. Interestingly, Aven is also a substrate of the ATM kinase. Mutation of ATM-mediated phosphorylation sites on Aven reduced its ability to activate ATM, suggesting that Aven activation of ATM after DNA damage is enhanced by ATM-mediated Aven phosphorylation.

CONCLUSIONS

These results identify Aven as a new ATM activator and describe a positive feedback loop operating between Aven and ATM. In aggregate, these findings place Aven, a known apoptotic inhibitor, as a critical transducer of the DNA-damage signal.

Nutrient deprivation induces autophagy as well as apoptosis in Chinese hamster ovary cell culture

During Chinese hamster ovary (CHO) cell culture for foreign protein production, cells are subjected to programmed cell death (PCD). A rapid death at the end of batch culture is accelerated by nutrient starvation. In this study, type II PCD, autophagy, as well as type I PCD, apoptosis, was found to take place in two antibody-producing CHO cell lines, Ab1 and Ab2, toward the end of batch culture when glucose and glutamine were limiting. The evidence of autophagy was observed from the accumulation of a common autophagic marker, a 16 kDa form of LC3-II during batch culture. Moreover, a significant percentage of the total cells (80% of Ab1 cells and 86% of Ab2 cells) showed autophagic vacuoles containing cytoplasmic material by transmission electron microscopy. An increased level of PARP cleavage and chromosomal DNA fragmentation supported that starvation-induced apoptosis also occurred simultaneously with autophagy.

Identification of unique gene expression patterns within different lesional sites of keloids

Keloid disease is a significant clinical problem, especially in black populations, with an estimated incidence of 4-16%. Keloids are fibroproliferative dermal tumors developing as a result of deregulated wound healing. The dynamic nature of keloids is illustrated by clinical regression in the center, while the margin remains active growing into the surrounding healthy skin. Therefore, the gene expression profiles of fibroblasts from different sites of the keloids were characterized using Affymetrix microarrays covering the whole human genome. This study revealed 105 genes that were differentially regulated (79 genes were up-regulated and 26 down-regulated) in a unique gene expression profile in different sites of keloids where progression or regression of the process was in progress. The apoptosis inhibitor AVEN was found to be up-regulated at the active margin of keloids, while apoptosis-inducing genes such as ADAM12 and genes inducing extracellular matrix (ECM) degradation such as matrix metalloproteinase-19 were up-regulated in the regressing keloid center. We identified genes previously not described in the development of keloids. Activating proapoptotic genes or inhibiting ECM-inducing genes as INHBA or monocyte chemoattractant protein-1 might be possible target genes for new treatment strategies for keloid disease.

Anti-apoptotic genes Aven and E1B-19K enhance performance of BHK cells engineered to express recombinant factor VIII in batch and low perfusion cell culture

The engineering of production cell lines to express anti-apoptotic genes has been pursued in recent years due to potential process benefits, including enhanced cell survival, increased protein expression, and improved product quality. In this study, a baby hamster kidney cell line secreting recombinant factor VIII (BHK-FVIII) was engineered to express the anti-apoptotic genes Aven and E1B-19K. In high cell density shake flask culture evaluation, 11 clonal cell lines expressing either E1B-19K or a combination of Aven and E1B-19K showed improved survival compared to both parental and blank vector cell line controls. These cell lines exhibited lower caspase-3 activation and reduced Annexin-V binding compared to the controls. Parental and blank vector cell lines were less than 50% viable after 48 h of exposure to thapsigargin while cell lines expressing E1B-19K with or without Aven maintained viabilities approaching 90%. Subsequently, the best Aven-E1B-19K candidate cell line was compared to the parental cell line in 12-L perfusion bioreactor studies. Choosing the appropriate perfusion rates in bioreactors is a bioprocess optimization issue, so the bioreactors were operated at sequentially lower specific perfusion rates, while maintaining a cell density of 2 x 10(7) viable cells/mL. The viability of the parental cell line declined from nearly 100% at a perfusion rate of 0.5 nL/cell/day to below 80% viability, with caspase-3 activity exceeding 15%, at its lower perfusion limit of 0.15 nL/cell/day. In contrast, the Aven-E1B-19K cell line maintained an average viability of 94% and a maximum caspase-3 activity of 2.5% even when subjected to a lower perfusion minimum of 0.1 nL/cell/day. Factor VIII productivity, specific growth rate, and cell size decreased for both cell lines at lower perfusion rates, but the drop in all cases was larger for the parental cell line. Specific consumption of glucose and glutamine and production of lactate were consistently lower for the Aven-E1B-19K culture. Furthermore, the yield of ammonia from glutamine increased for the Aven-E1B-19K cell line relative to the parent to suggest altered metabolic pathways following anti-apoptosis engineering. These results demonstrate that expression of anti-apoptotic genes Aven and E1B-19K can increase the stability and robustness of an industrially relevant BHK-FVIII mammalian cell line over a wide range of perfusion rates.

Glutamine Regulates the Human Epithelial Intestinal HCT-8 Cell Proteome under Apoptotic Conditions

Glutamine plays a key role in the metabolism of rapidly dividing cells, including enterocytes and lymphocytes, which may contribute to its beneficial clinical effects. Gut mucosal homeostasis is achieved through a balance between cell proliferation and apoptosis. In T cells, glutamine up-regulates antiapoptotic proteins and down-regulates proapoptotic proteins. In gut mucosa, glutamine prevents apoptosis in rat epithelial cell lines, whereas glutamine starvation induces apoptosis through caspase activation. Finally glutamine specifically prevents tumor necrosis factor-alpha-related apoptosis in the human intestinal cell line HT-29. Comparative functional proteomics enables the characterization of each differentially expressed protein in intestinal cells in response to modifications of nutritional environment. The influence of glutamine on intestinal proteome expression in apoptotic conditions has not been studied and evaluated. This comparative proteomics study was performed in the human epithelial intestinal cell line HCT-8 under experimental apoptotic conditions to investigate the influence of glutamine on protein expression during apoptosis. The pharmaconutritional effects of glutamine were determined under 2 mm (physiological concentration) and 10 mm (pharmaconutritional concentration) conditions. About 1,800 protein spots were revealed in both conditions. Comparative assessments indicated that 28 proteins were differentially expressed significantly (i.e. at least 2-fold modulated and Student's t test with p </= 0.05) in response to an increase of glutamine concentration in the culture medium. Twenty-four proteins were identified by mass spectrometry and associated databases. From these proteins, 34% are involved in cell cycle and apoptosis mechanisms, 17% are involved in signal transduction, and 13% are involved in cytoskeleton organization. These data were integrated in a proposed schema of the interactome under apoptotic conditions. In conclusion, this study provides the first holistic picture of proteome modulation by glutamine in a human enterocytic cell line under apoptotic conditions and supports further evaluation of nutritional modulation of human intestinal proteome in various pathological conditions where apoptosis may be involved.

Advancing mammalian cell culture engineering using genome-scale technologies

Mammalian cell-derived protein therapeutic production has changed the landscape of human healthcare in the past two decades. The importance of protein therapeutics has motivated the search for more cost-effective and efficient cell lines capable of producing high quality protein products. The factors contributing to optimal producer cell lines are often complex, and not simply conferred by one gene or gene product, which makes an understanding of system-wide properties for better engineering of optimized cell lines essential. Genome-scale technologies (genomics, transcriptomics and proteomics) enable such engineering studies. However, the use of these technologies in cell culture engineering is still in its infancy. Here, we summarize current knowledge of cell properties important for the design of efficient protein-producing mammalian cell lines, and highlight relevant studies to-date that use genome-scale technologies in these cell systems. We also provide a focused review of relevant alternative and emerging technologies, which have seen limited use in cell culture engineering, but hold great potential for significant advancements in protein therapeutic production.

Enhanced cell culture performance using inducible anti-apoptotic genes E1B-19K and Aven in the production of a monoclonal antibody with Chinese hamster ovary cells

Mammalian cells are used for the production of numerous biologics including monoclonal antibodies. Unfortunately, mammalian cells can lose viability at later stages in the cell culture process. In this study, the effects of expressing the anti-apoptosis genes, E1B-19K and Aven, separately and in combination on cell growth, survival, and monoclonal antibody (MAb) production were investigated for a commercial Chinese Hamster Ovary (CHO) mammalian cell line. CHO cells were observed to undergo apoptosis following a model insult, glucose deprivation, and at later stages of batch cell culture. The CHO cell line was then genetically modified to express the anti-apoptotic proteins E1B-19K and/or Aven using an ecdysone-inducible expression system. Stable transfected pools induced to express Aven or E1B-19K alone were found to survive 1-2 days longer than the parent cell line following glucose deprivation while the expression of both genes in concert increased cell survival by 3 days. In spinner flask batch studies, a clonal isolate engineered to express both anti-apoptosis genes exhibited a longer operating lifetime and higher final MAb titer as a result of higher viable cell densities and viabilities. Interestingly, survival was increased in the absence of an inducer, most likely as a result of leaky expression of the anti-apoptosis genes confirmed in subsequent PCR studies. In fed-batch bioreactors, the expression of both anti-apoptosis genes resulted in higher growth rates and cell densities in the exponential phase and significantly higher viable cell densities, viabilities, and extended survival during the post-exponential phase. As a result, the integral of viable cells (IVC) was between 40 and 100% higher for cell lines engineered to express both Aven and E1B-19K in concert, and the operational lifetime of the fed-batch bioreactors was increased from 2 to 5 days. The maximum titers of MAb were also increased by 40-55% for bioreactors containing cells expressing Aven and E1B-19K. These increases in volumetric productivity arose primarily from enhancements in viable cell density over the course of the fed-batch culture period since the specific productivities for the cells expressing anti-apoptosis genes were comparable or slightly lower than the parental hosts. These results demonstrate that expression of anti-apoptosis genes can enhance culture performance and increase MAb titers for mammalian CHO cell cultures especially under conditions such as extended fed-batch bioreactor operation.

Targeted genetic modification of cell lines for recombinant protein production

Considerable increases in productivity have been achieved in biopharmaceutical production processes over the last two decades. Much of this has been a result of improvements in media formulation and process development. Though advances have been made in cell line development, there remains considerable opportunity for improvement in this area. The wealth of transcriptional and proteomic data being generated currently hold the promise of specific molecular interventions to improve the performance of production cell lines in the bioreactor. Achieving this-particularly for multi-gene modification-will require specific, targeted and controlled genetic manipulation of these cells. This review considers some of the current and potential future techniques that might be employed to realise this goal.

Using cell engineering and omic tools for the improvement of cell culture processes

Significant strides have been made in mammalian cell based biopharmaceutical process and cell line development over the past years. With several established mammalian host cell lines and expression systems, optimization of selection systems to reduce development times and improvement of glycosylation patterns are only some of the advances being made to improve cell culture processes. In this article, the advances pertaining to cell line development and cell engineering strategies are discussed. An overview of the cell engineering strategies to enhance cellular characteristics by genetic manipulation are illustrated, focusing on the use of genomics and proteomics tools and their application in such endeavors. Included in this review are some of the early studies using the 'omic' technique to understand cellular mechanisms of product synthesis and secretion, apoptosis, cell proliferation and the influence of the physicochemical environment. The article highlights the significance of integrating genomics and proteomics data with the vast amounts of bioprocess data for improved analysis of the biological pathways involved. Further improvements of the techniques and methodologies used are needed but ultimately, the new cell engineering strategies should provide great insight into the regulatory networks within the cell in a bioprocess environment and how to manipulate them to increase overall productivity.

Inhibiting the apoptosis pathway using MDM2 in mammalian cell cultures

The ability to regulate apoptosis in mammalian cell cultures represents one approach to developing more economical and efficient processes. Genetic modification of cells using anti-apoptotic genes is one method that may be used to improve cellular performance. This study investigates a method to inhibit upstream apoptosis pathways through the overexpression of MDM2, an E3 ubiquitin ligase for p53. Both 293 and CHO cells expressing MDM2 were examined under both batch and spent media conditions. For batch cultures, MDM2 overexpression increased viable cell densities and viabilities over control cells with the largest enhancements observed in CHO cells. When CHO cells were passaged without medium exchange, cells expressing MDM2 reached a viable cell density that was nearly double the control and survived for an extra day in culture. When exposed to spent media initially, both 293-MDM2 and CHO-MDM2 cells continued to grow for 2 days while the control cells stopped growing after the first day. DNA analysis using flow cytometry confirmed that while CHO controls were found to be undergoing DNA fragmentation, CHO-MDM2 cells exhibit DNA degradation at a much slower rate. When compared to Bcl-2-expressing cells, MDM2 expression showed greater protection against apoptosis in passaged culture, spent medium, and following transient p53 overexpression. However, expression of the RING sequence of MDM2 responsible for E3 ligase activity without the other components of the protein was found to be toxic to 293 cells in culture. These results suggest that the overexpression of heterologous MDM2 represents a promising method to delay apoptosis in mammalian cell cultures.

Combining caspase and mitochondrial dysfunction inhibitors of apoptosis to limit cell death in mammalian cell cultures

Apoptosis is now recognized as a significant problem in mammalian cell culture. Therefore, in this study, a single gene and multigene approach to inhibit apoptosis has been examined. Stable Chinese hamster ovary (CHO) cell lines were generated to overexpress different single, dual, and triple combinations of three apoptosis inhibitor genes. Two upstream inhibitors involved in the mitochondrial pathway, Bcl-X(L) and Aven, were expressed in addition to a downstream inhibitor of caspases. The caspase inhibitor, a variant of XIAP containing only the caspase inhibitory BIR domains (XIAP-BIRs), has been shown previously to enhance viabilities in mammalian cultures. Stable clonal cell lines were generated and tested for three apoptotic insults: Sindbis virus infection, the chemical reagent etoposide, and spent medium. For all single gene experiments, the Bcl-X(L)-containing cell lines provided superior protection to either the Aven- or XIAP-BIRs-containing cell lines following initial exposure to the insults. However, the cell lines expressing two or more anti-apoptosis proteins were more effective at inhibiting cell death than those expressing just one anti-apoptosis gene. The cell lines overexpressing Bcl-X(L) in combination with XIAP-BIRs were especially effective in delaying cell death for all three apoptotic insults. Expression of all three anti-apoptosis genes in concert was only slightly more effective than using Bcl-X(L) and XIAP-BIRs for some insults. During exposure to spent medium, CHO-BIRS + Aven + BclX(L) was the best inhibitor of apoptosis (IAP) initially, whereas CHO-BIRs + BclX(L) was particularly effective at later times of the experiment. In conclusion, the utilization of a mitochondrial dysfunction inhibitor used in combination with a caspase inhibitor was more effective in thwarting the progression of apoptosis than either inhibitor expressed individually. Thus, the concurrent expression of multiple apoptosis inhibitors may be the most effective strategy to increase survival of mammalian cells in culture.

RNAi suppression of Bax and Bak enhances viability in fed-batch cultures of CHO cells

Bcl-2 family proteins play a crucial role in the regulation of the mitochondrial pathway that leads to apoptosis. Members of the Bcl-2 family can be divided into the anti-apoptotic proteins such as Bcl-2 and Bcl-X(L), and the pro-apoptotic proteins such as Bax and Bak and the BH3-only proteins. In this study, siRNA constructs to silence the Bax and Bak genes in Chinese hamster ovary (CHO) cells were generated. Stable CHO cell lines in which the expression of Bax and Bak were significantly knocked down were screened by Western blot analysis and confirmed by RT-PCR. CHO cells with both Bax and Bak knocked down showed a clear resistance against cytotoxic lectins and UV irradiation-induced apoptosis. Compared to original CHO-K1 cells, these cells also survived longer when cultured under extreme conditions such as complete nutrient depletion or in high-osmolality medium. CHO cells with both Bax and Bak genes knocked down displayed an extended lifespan as well as higher viable cell densities in fed-batch cultures, both in adherent form on microcarrier beads and in suspension. The IFN-gamma productivity by a rCHO IFN-gamma cell line in which both Bak and Bax were knocked down increased by 35% compared to the control cells. These results indicate that the genetic inactivation of Bax and Bak in recombinant CHO cells can be an effective strategy in delaying the onset of apoptosis in batch and fed-batch cultures.

Correlation of Heavy and Light Chain mRNA Copy Numbers to Antibody Productivity in Mouse Myeloma Production Cell Lines

Manufacturing cell line development at Centocor involves transfection of antibody genes into host cell lines and isolating primary transfectomas that upon subcloning yield high expressing cell lines for the desired antibody. In an attempt to increase productivity of these cell lines, we set out to identify the rate-limiting step in the process of antibody expression and secretion. For this purpose, 30 antibody expressing cell lines with variable antibody expression levels were analyzed for heavy-chain and light-chain mRNA expression levels. Results suggested that the increase in antibody titer of the subclones (compared to their primary clones) was partly due to an increase in heavy-chain and light-chain mRNA levels; higher expressers were associated with approximately 1.0 x 10(7) and 1.5 x 10(7) copies of heavy-chain and light-chain per 10 nanogram of cDNA, respectively. Generally, the level of light-chain mRNA was higher compared to the level of heavy-chain mRNA in a majority of the cell lines, and the difference in their levels was not due to their differential stability. The data generated from all the cell lines tested in this study suggested that there was a correlation of light-chain and heavy-chain transcript levels to antibody productivity, with the coefficient of correlation being 0.59 for light chain and 0.81 for heavy chain. We conclude that transcription of heavy chain and to a lesser extent light chain could be one of the rate-limiting steps in the antibody expression pathway. Hence, methods that would increase these mRNA levels could be beneficial in the attempt to improve the antibody expression level of production cell lines.

Engineering cells for cell culture bioprocessing--physiological fundamentals

In the past decade, we have witnessed a tremendous increase in the number of mammalian cell-derived therapeutic proteins with clinical applications. The success of making these life-saving biologics available to the public is partly due to engineering efforts to enhance process efficiency. To further improve productivity, much effort has been devoted to developing metabolically engineered producing cells, which possess characteristics favorable for large-scale bioprocessing. In this article we discuss the fundamental physiological basis for cell engineering. Different facets of cellular mechanisms, including metabolism, protein processing, and the balancing pathways of cell growth and apoptosis, contribute to the complex traits of favorable growth and production characteristics. We present our assessment of the current state of the art by surveying efforts that have already been undertaken in engineering cells for a more robust process. The concept of physiological homeostasis as a key determinant and its implications on cell engineering is emphasized. Integrating the physiological perspective with cell culture engineering will facilitate attainment of dream cells with superlative characteristics.

Targeting early apoptotic genes in batch and fed-batch CHO cell cultures

Based on the transcriptional profiling of CHO cell culture using microarray, four key early apoptosis signaling genes, Fadd, Faim, Alg-2, and Requiem, were identified and CHO GT (Gene Targeted) cell lines were developed by targeting these four genes. Two were CHO GT(O) cell lines overexpressing anti-apoptotic genes, Faim and Fadd DN and two were CHO GT(KD) cell lines involving knockdown of Alg-2 and Requiem which are pro-apoptotic genes using small interfering RNA (siRNA) technology. Comparisons of these CHO GT cell lines with the parental cell line in batch culture (BC) and fed-batch culture (FBC) were performed. Compared to parental cells, the CHO GT cell lines showed apoptosis resistance as they significantly delayed and/or suppressed initiator caspase-8 and -9 and executioner caspase-3 activities during culture. FBC of CHO GT cell lines reached significantly higher maximum viable cell densities (up to 9 x 10(6) cells/mL) compared with the parental cell line (5 x 10(6) cells/mL). The recombinant interferon gamma (IFN-gamma) yields were increased by up to 2.5-fold. Furthermore, it was observed that the IFN-gamma was more highly sialylated.

Bcl-x(L) mediates increased production of humanized monoclonal antibodies in Chinese hamster ovary cells

Enhanced product yields, reduction in throughput time, improved cost-effectiveness and product quality are examples of benefits gained by delaying apoptotic cell death in bioreactors. To examine the effect on recombinant protein production, bcl-x(L) was overexpressed in a CHO cell line secreting humanized monoclonal antibody directed against the alpha1beta1 integrin. When cell lines overexpressing bcl-x(L) were compared to the parent, cell viability was increased by 20% and titers by 80%. Total viable cell densities were similar and specific productivities were enhanced by almost two-fold on scale-up to bioreactors. Comparison in a chemically defined media demonstrated an even greater sustained viability in bcl-x(L) expressing cells by 50% and up to 90% increase in titer with no impact on product quality. Caspase 3 activities were monitored as a marker for apoptotic cell death. In the presence of Bcl-x(L), caspase activities were reduced to background levels. The role of Bcl-x(L) in protecting cells from premature death was further examined in studies performed in the presence of NaBu, at concentrations known to trigger cell death. Results demonstrated that cells expressing bcl-x(L) retained 88% cell viability with >2 fold increase in titer. Bcl-x(L) was similarly overexpressed in a different CHO cell line producing a humanized mAb against the chemokine MCP1. Once again, production titer was increased by 80% and viability by 75%. Together the studies have shown that overexpression of bcl-x(L) in production cell lines was able to significantly increase the titer by enhancing both the specific activity and total cell viability while maintaining product quality.

Production technologies for monoclonal antibodies and their fragments

In recent years, monoclonal antibodies have emerged as an increasingly important class of human therapeutics. A variety of forms of antibodies, including fragments such as Fabs, Fab'2s and single-chain Fvs, are also being evaluated for a range of different purposes. A variety of expression systems and improvements within these systems have been developed to address these growing and diverse needs.

Effects of IKK inhibitor PS1145 on NF-κB function, proliferation, apoptosis and invasion activity in prostate carcinoma cells

A key antiapoptotic transcription factor, nuclear factor kappa-B (NF-kappaB), is known to be critically important for tumor cell growth, angiogenesis and development of metastatic lesions. We and others showed previously that NF-kappaB transcription factor was constitutively activated in androgen-independent prostate carcinoma (PC) cell lines due to the upregulated activity of inhibitor of NF-kappaB kinases (IKK). In this work, using luciferase assay, electrophoretic mobility shift assay and Northern blot analysis of expression of endogenous kappaB-responsive genes, we demonstrate that a novel highly specific small-molecule IKK inhibitor, PS1145, efficiently inhibited both basal and induced NF-kappaB activity in PC cells. We found that PS1145 induced caspase 3/7-dependent apoptosis in PC cells and significantly sensitized PC cells to apoptosis induced by tumor necrosis factor alpha. We also showed that PS1145 inhibited PC cell proliferation. Effects of PS1145 on proliferation and apoptosis correlated with inhibition of interleukin (IL)-6, cyclin D1, D2, inhibitor of apoptosis (IAP)-1 and IAP-2 gene expression and decreased IL-6 protein level. In addition, we found that incubation with PS1145 inhibited the invasion activity of highly invasive PC3-S cells in invasion chamber assay in a dose-dependent manner. Overall, this study provides the framework for development of a novel therapeutic approach targeting NF-kappaB transcription factor to treat advanced PC.