Overexpression of transcription factor Foxa1 and target genes remediate therapeutic protein production bottlenecks in Chinese hamster ovary cells

Molecular biomarkers identification and applications in CHO bioprocessing

Biomarkers are valuable tools in clinical research where they allow to predict susceptibility to diseases, or response to specific treatments. Likewise, biomarkers can be extremely useful in the biomanufacturing of therapeutic proteins. Indeed, constraints such as short timelines and the need to find hyper-productive cells could benefit from a data-driven approach during cell line and process development. Many companies still rely on large screening capacities to develop productive cell lines, but as they reach a limit of production, there is a need to go from empirical to rationale procedures. Similarly, during bioprocessing runs, substrate consumption and metabolism wastes are commonly monitored. None of them possess the ability to predict the culture behavior in the bioreactor. Big data driven approaches are being adapted to the study of industrial mammalian cell lines, enabled by the publication of Chinese hamster and CHO genome assemblies which allowed the use of next-generation sequencing with these cells, as well as continuous proteome and metabolome annotation. However, if these different -omics technologies contributed to the characterization of CHO cells, there is a significant effort remaining to apply this knowledge to biomanufacturing methods. The correlation of a complex phenotype such as high productivity or rapid growth to the presence or expression level of a specific biomarker could save time and effort in the screening of manufacturing cell lines or culture conditions. In this review we will first discuss the different biological molecules that can be identified and quantified in cells, their detection techniques, and associated challenges. We will then review how these markers are used during the different steps of cell line and bioprocess development, and the inherent limitations of this strategy.

FOXA1 Suppresses Endoplasmic Reticulum Stress, Oxidative Stress, and Neuronal Apoptosis in Parkinson's Disease by Activating PON2 Transcription

Endoplasmic reticulum (ER) stress and oxidative stress (OS) are often related states in pathological conditions including Parkinson's disease (PD). This study investigates the role of anti-oxidant protein paraoxonase 2 (PON2) in ER stress and OS in PD, along with its regulatory molecule. PD was induced in C57BL/6 mice using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) treatment and in SH-SY5Y cells using 1-methyl-4-phenylpyridinium. PON2 was found to be poorly expressed in the substantia nigra pars compacta (SNc) of PD mice, and its overexpression improved motor coordination of mice. Through the evaluation of tyrosine hydroxylase, dopamine transporter, reactive oxygen species (ROS), and C/EBP homologous protein (CHOP) levels and neuronal loss in mice, as well as the examination of CHOP, glucose-regulated protein 94 (GRP94), GRP78, caspase-12, sarco/endoplasmic reticulum calcium ATPase 2, malondialdehyde, and superoxide dismutase levels in SH-SY5Y cells, we observed that PON2 overexpression mitigated ER stress, OS, and neuronal apoptosis both in vivo and in vitro. Forkhead box A1 (FOXA1) was identified as a transcription factor binding to the PON2 promoter to activate its transcription. Upregulation of FOXA1 similarly protected against neuronal loss by alleviating ER stress and OS, while the protective roles were abrogated by additional PON2 silencing. In conclusion, this study demonstrates that FOXA1-mediated transcription of PON2 alleviates ER stress and OS, ultimately reducing neuronal apoptosis in PD.

Synergistic promotion of transient transgene expression in CHO cells by PDI/XBP-1s co-transfection and mild hypothermia

Transient gene expression system is an important tool for rapid production of recombinant proteins in Chinese hamster ovary (CHO) cells. However, their low productivity is the main hurdle to overcome. An effective approach through which to obtain high protein yield involves targeting transcriptional, post-transcriptional events (PTEs), and culture conditions. Here, we investigated the effects of protein disulfide isomerase (PDI) and spliced X-box binding protein 1 (XBP-1s) co-overexpression combined with mild hypothermia on the transient yields of recombinant proteins in CHO cells. The results showed that the gene of interest (GOI) and the PDI/XBP-1s helper vector at a co-transfection ratio of 10:1 could obviously increase transient expression level of recombinant protein in CHO cells. However, PDI/XBP-1s overexpression had no significance effect on the mRNA levels of the recombinant protein, suggesting that it targeted PTEs. Moreover, the increased production was due to the enhancing of cell specific productivity, not related to cell growth, viability, and cell cycle. In addition, combined PDI/XBP-1s co-overexpression and mild hypothermia could further improve Adalimumab expression, compared to the control/37 °C and PDI/XBP-1s/37 °C, the Adalimumab volume yield of PDI/XBP-1s/33 °C increased by 203% and 142%, respectively. Mild hypothermia resulted in 3.52- and 2.33-fold increase in the relative mRNA levels of PDI and XBP-1s, respectively. In conclusion, the combination of PDI/XBP-1s overexpression and culture temperature optimization can achieve higher transient expression of recombinant protein, which provides a synergetic strategy to improve transient production of recombinant protein in CHO cells.

Mitigating transcriptional bottleneck using a constitutively active transcription factor, VP16-CREB, in mammalian cells

High-level expression of recombinant proteins in mammalian cells has long been an area of interest. Inefficient transcription machinery is often an obstacle in achieving high-level expression of recombinant proteins in mammalian cells. Synthetic promoters have been developed to improve the transcription efficiency, but have achieved limited success due to the limited availability of transcription factors (TFs). Here, we present a TF-engineering approach to mitigate the transcriptional bottlenecks of recombinant proteins. This includes: (i) identification of cAMP response element binding protein (CREB) as a candidate TF by searching for TFs enriched in the cytomegalovirus (CMV) promoter-driven high-producing recombinant Chinese hamster ovary (rCHO) cell lines via transcriptome analysis, (ii) confirmation of transcriptional limitation of active CREB in rCHO cell lines, and (iii) direct activation of the transgene promoter by expressing constitutively active CREB at non-cytotoxic levels in rCHO cell lines. With the expression of constitutively active VP16-CREB, the production of therapeutic proteins, such as monoclonal antibody and etanercept, in CMV promoter-driven rCHO cell lines was increased up to 3.9-fold. VP16-CREB was also used successfully with synthetic promoters containing cAMP response elements. Taken together, this strategy to introduce constitutively active TFs into cells is a useful means of overcoming the transcriptional limitations in recombinant mammalian cells.

Recent advances in the application of genetic and epigenetic modalities in the improvement of antibody-producing cell lines

There are numerous applications for recombinant antibodies (rAbs) in biological and toxicological research. Monoclonal antibodies are synthesized using genetic engineering and other related processes involved in the generation of rAbs. Because they can identify specific antigenic sites on practically any molecule, including medicines, hormones, microbial antigens, and cell receptors, rAbs are particularly useful in scientific research. The key benefits of rAbs are improved repeatability, control, and consistency, shorter manufacturing times than with hybridoma technology, an easier transition from one format of antibody to another, and an animal-free process. The engineering of the host cell has recently been developed method for enhancing the production efficiency and improving the quality of antibodies from mammalian cell lines. In this light, genetic engineering is mostly utilized to manage cellular chaperones, decrease cell death, increase cell viability, change the microRNAs (miRNAs) pattern in mammalian cells, and glycoengineered cell lines. Here, we shed light on how genetic engineering can be used therapeutically to produce antibodies at higher levels with greater potency and effectiveness.

Identification of Small Molecules Affecting the Secretion of Therapeutic Antibodies with the Retention Using Selective Hook (RUSH) System

Unlocking cell secretion capacity is of paramount interest for the pharmaceutical industry focused on biologics. Here, we leveraged retention using a selective hook (RUSH) system for the identification of human osteosarcoma U2OS cell secretion modulators, through automated, high-throughput screening of small compound libraries. We created a U2OS cell line which co-expresses a variant of streptavidin addressed to the lumen-facing membrane of the endoplasmic reticulum (ER) and a recombinant anti-PD-L1 antibody. The heavy chain of the antibody was modified at its C-terminus, to which a furin cleavage site, a green fluorescent protein (GFP), and a streptavidin binding peptide (SBP) were added. We show that the U2OS cell line stably expresses the streptavidin hook and the recombinant antibody bait, which is retained in the ER through the streptavidin-SBP interaction. We further document that the addition of biotin to the culture medium triggers the antibody release from the ER, its trafficking through the Golgi where the GFP-SBP moiety is clipped off, and eventually its release in the extra cellular space, with specific antigen-binding properties. The use of this clone in screening campaigns led to the identification of lycorine as a secretion enhancer, and nigericin and tyrphostin AG-879 as secretion inhibitors. Altogether, our data support the utility of this approach for the identification of agents that could be used to improve recombinant production yields and also for a better understanding of the regulatory mechanism at work in the conventional secretion pathway.

Engineering of Chinese hamster ovary cells for co-overexpressing MYC and XBP1s increased cell proliferation and recombinant EPO production

Improving the cellular capacity of Chinese hamster ovary (CHO) cells to produce large amounts of therapeutic proteins remains a major challenge for the biopharmaceutical industry. In previous studies, we observed strong correlations between the performance of CHO cells and expression of two transcription factors (TFs), MYC and XBP1s. Here, we have evaluated the effective of overexpression of these two TFs on CHO cell productivity. To address this goal, we generated an EPO-producing cell line (CHO_EPO) using a targeted integration approach, and subsequently engineered it to co-overexpress MYC and XBP1s (a cell line referred to as CHOCX_EPO). Cells overexpressing MYC and XBP1s increased simultaneously viable cell densities and EPO production, leading to an enhanced overall performance in cultures. These improvements resulted from the individual effect of each TF in the cell behaviour (i.e., MYC-growth and XBP1s-productivity). An evaluation of the CHOCX_EPO cells under different environmental conditions (temperature and media glucose concentration) indicated that CHOCX_EPO cells increased cell productivity in high glucose concentration. This study showed the potential of combining TF-based cell engineering and process optimisation for increasing CHO cell productivity.

A Comprehensive Bioinformatic Analysis for Identification of Myeloid-Associated Differentiation Marker as a Potential Negative Prognostic Biomarker in Non-Small-Cell Lung Cancer

Objectives: This study aimed to identify a molecular marker associated with the prognosis of non-small-cell lung cancer (NSCLC).

Materials and Methods: The RNA sequencing data and clinical information of NSCLC patients were obtained from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO). The weighted gene co-expression network analysis (WGCNA) was used to identify the co-expression gene modules and differentially expressed genes (DEGs) by comparing gene expression between NSCLC tumor tissues and normal tissues. Subsequently, the functional enrichment analysis of the DEGs was performed. Kaplan-Meier survival analysis and the GEPIA2 online tool were performed to investigate the relationship between the expression of these genes of interest and the survival of NSCLC patients, and to validate one most survival-relevent hub gene, as well as validated the hub gene using independent datasets from the GEO database. Further analysis was carried out to characterize the relationship between the hub gene and tumor immune cell infiltration, tumor mutation burden (TMB), microsatellite instability (MSI), and other known biomarkers of lung cancer. The related genes were screened by analyzing the protein-protein interaction (PPI) network and the survival model was constructed. GEPIA2 was applied in the potential analysis of pan-cancer biomarker of hub gene.

Results: 57 hub genes were found to be involved in intercellular connectivity from the 779 identified differentially co-expressed genes. Myeloid-associated differentiation marker (MYADM) was strongly associated with overall survival (OS) and disease-free survival (DFS) of NSCLC patients, and high MYADM expression was associated with poor prognosis. Thus, MYADM was identified as a risk factor. Additionally, MYADM was validated as a survival risk factor in NSCLC patients in two independent datasets. Further analysis showed that MYADM was nagetively associated with TMB, and was positively correlated with macrophages, neutrophils, and dendritic cells, suggesting its role in regulating tumor immunity. The MYADM expression differed across many types of cancer and had the potential to serve as a pan-cancer marker.

Conclusion:MYADM is an independent prognostic factor for NSCLC patients, which can predict the progression of cancer and play a role in the tumor immune cell infiltration in NSCLC.

The secretory pathway - the key for unlocking the potential of Chinese hamster ovary cell factories for manufacturing therapeutic proteins

Mammalian cell factories (in particular the CHO cell system) have been crucial in the rise of biopharmaceuticals. Mammalian cells have compartmentalized organelles where intricate networks of proteins manufacture highly sophisticated biopharmaceuticals in a specialized production pipeline - the secretory pathway. In the bioproduction context, the secretory pathway functioning is key for the effectiveness of cell factories to manufacture these life-changing medicines. This review describes the molecular components and events involved in the secretory pathway, and provides a comprehensive summary of the intracellular steps limiting the production of therapeutic proteins as well as the achievements in engineering CHO cell secretory machinery. We also consider antibody-producing plasma cells (so called "professional" secretory cells) to explore the mechanisms underpinning their unique secretory function/features. Such understandings offer the potential to further enhancement of the current CHO cell production platforms for manufacturing next generation of biopharmaceuticals.

Restoration of DNA repair mitigates genome instability and increases productivity of Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells are the primary host for manufacturing of therapeutic proteins. However, productivity loss is a major problem and is associated with genome instability, as chromosomal aberrations reduce transgene copy number and decrease protein expression. We analyzed whole-genome sequencing data from 11 CHO cell lines and found deleterious single-nucleotide variants in DNA repair genes. Comparison with primary Chinese hamster cells confirmed DNA repair to be compromised in CHO. Correction of key DNA repair genes by single-nucleotide variant reversal or expression of intact complementary DNAs successfully improved DNA repair and mitigated karyotypic instability. Moreover, overexpression of intact copies of LIG4 and XRCC6 in a CHO cell line expressing secreted alkaline phosphatase mitigated transgene copy loss and improved protein titer retention. These results show that correction of DNA repair genes yields improvements in genome stability in CHO, and provide new opportunities for cell line development for sustainable protein expression.

Improving the secretory capacity of CHO producer cells: The effect of controlled Blimp1 expression, a master transcription factor for plasma cells

With the advent of novel therapeutic proteins with complex structures, cellular bottlenecks in secretory pathways have hampered the high-yield production of difficult-to-express (DTE) proteins in CHO cells. To mitigate their limited secretory capacity, recombinant CHO (rCHO) cells were engineered to express Blimp1, a master regulator orchestrating B cell differentiation into professional secretory plasma cells, using the streamlined CRISPR/Cas9-based recombinase-mediated cassette exchange landing pad platform. The expression of Blimp1α or Blimp1β in rCHO cells producing DTE recombinant human bone morphogenetic protein-4 (rhBMP-4) increased specific rhBMP-4 productivity (q_rhBMP-4). However, since Blimp1α expression suppressed cell growth more significantly than Blimp1β expression, only Blimp1β expression enhanced rhBMP-4 yield. In serum-free suspension culture, Blimp1β expression significantly increased the rhBMP-4 concentration (>3-fold) and q_rhBMP-4 (>4-fold) without significant increase in hBMP-4 transcript levels. In addition, Blimp1β expression facilitated mature rhBMP-4 secretion by active proteolytic cleavage in the secretory pathway. Transcriptomic profiling (RNA-seq) revealed global changes in gene expression patterns that promote protein processing in secretory organelles. In-depth integrative analysis of the current RNA-seq data, public epigenome/RNA-seq data, and in silico analysis identified 45 potential key regulators of Blimp1 that are consistently up- or down-regulated in Blimp1β expressing rCHO cells and plasma cells. Blimp1β expression also enhanced the production of easy-to-express monoclonal antibodies (mAbs) and modulated the expression of key regulators in rCHO cells producing mAb. Taken together, the results show that controlled expression of Blimp1β improves the production capacity of rCHO cells by regulating secretory machinery and suggest new opportunities for engineering promising targets that are resting in CHO cells.

From omics to Cellular mechanisms in mammalian cell factory development

Mammalian cells have been used widely as biopharmaceutical cell factories due to their ability to make complex biotherapeutic proteins with human-compatible modifications. However, their application for some products has been hampered by low protein yields. Numerous studies have aimed to characterize cellular bottlenecks in the hope of boosting protein productivity, but the complexity of the underlying pathways and the diversity of the modifications have complicated cell engineering when relying solely on traditional methodologies. Incorporating omics-based and systems approaches into cell engineering can provide valuable insights into desirable phenotypes of cell factories. Here, we discuss cell engineering strategies for enhancing protein productivity in mammalian cell factories, particularly CHO and HEK293, and the opportunities and limitations of the genome-wide screening and multi-omics approaches for guiding cell engineering. Systems biology strategies will also be discussed to show how they refine our understanding of the cellular mechanisms which will aid in effective engineering strategies.

High FOXA1 immunohistochemical expression level associates with mucinous histology, favorable clinico-pathological prognostic parameters and survival advantage in epithelial ovarian cancer

Background

Forkhead box (FOX) A1 is a potential therapeutic biomarker that has been investigated in various human cancers. Limited data exist about FOXA1 biologic role in epithelial ovarian cancer (EOC).

Aim

This study assessed FOXA1 immunohistochemical (IHC) expression and evaluated its association with clinico-pathological parameters in EOC including overall and disease-free survivals (OS, DFS) and patient’s outcome.

Methods

Patient’s socio-epidemiologic, clinical, radiological, laboratory, surgical, and follow-up data were collected. After histopathologic typing, grading and staging, FOXA1 IHC expression was scored in 98 EOC specimens. Clinico-pathological associations were investigated in high-and low-FOXA1 expression groups using appropriate statistical methods. Kaplan-Meier method was used for survival analysis.

Results

FOXA1 tumor cell nuclear staining was detected in 63.3% of EOC with weak, moderate and strong scores (28.6%, 12.2% and 22.5% respectively). Comparing high- and low-expression groups (34.7% and 65.3% respectively), high FOXA1 was associated with larger tumors, low mean serum CA-125, tumor histopathology (mucinous and low-grade serous), type I EOC, limited tumor’s anatomical extent, absence of nodal or distant metastases and omental nodules, earlier FIGO stages, non-recurrent tumors and survival advantage with longer and OS and DFS (all p ≤ 0.05). Independent predictors of high FOXA1 expression included: omental nodules, tumor’s anatomical extent and tumor’s size (p ≤ 0.001, = 0.046 and = 0.023 respectively).

Conclusion

FOXA1 is frequently expressed in EOC notably mucinous and low-grade serous carcinomas in association with favorable prognostic clinico-pathological parameters and longer OS and DFS. It likely has a suppressor function in EOC and could be recommended as a prognostic and therapeutic biomarker.

A novel hydrogen peroxide evolved CHO host can improve the expression of difficult to express bispecific antibodies

The manufacture of bispecific antibodies by Chinese hamster ovary (CHO) cells is often hindered by lower product yields compared to monoclonal antibodies. Recently, reactive oxygen species have been shown to negatively impact antibody production. By contrast, strategies to boost cellular antioxidant capacity appear to be beneficial for recombinant protein expression. With this in mind, we generated a novel hydrogen peroxide evolved host using directed host cell evolution. Here we demonstrate that this host has heritable resistance to hydrogen peroxide over many generations, displays enhanced antioxidant capacity through the upregulation of several, diverse antioxidant defense genes such as those involved in glutathione synthesis and turnover, and has improved glutathione content. Additionally, we show that this host has significantly improved transfection recovery times, improved growth and viability properties in a fed‐batch production process, and elevated expression of two industrially relevant difficult to express bispecific antibodies compared to unevolved CHO control host cells. These findings demonstrate that host cell evolution represents a powerful methodology for improving specific host cell characteristics that can positively impact the expression of difficult to express biotherapeutics.

Cell culture bioprocessing - the road taken and the path forward

Cell culture processes are used to produce the vast majority of protein therapeutics, valued at over US$180 billion per annum worldwide. For more than a decade now, these processes have become highly productive. To further enhance capital efficiency, there has been an increase in the adoption of disposable apparatus and continuous processing, as well as a greater exploration of in-line sensing, various -omic tools, and cell engineering to enhance process controllability and product quality consistency. These feats in cell culture processing for protein biologics will help accelerate the bioprocess advancements for virus and cell therapy applications.

High-resolution three-dimensional chromatin profiling of the Chinese hamster ovary cell genome

Chinese hamster ovary (CHO) cell lines are the pillars of a multibillion‐dollar biopharmaceutical industry producing recombinant therapeutic proteins. The effects of local chromatin organization and epigenetic repression within these cell lines result in unpredictable and unstable transgene expression following random integration. Limited knowledge of the CHO genome and its higher order chromatin organization has thus far impeded functional genomics approaches required to tackle these issues. Here, we present an integrative three‐dimensional (3D) map of genome organization within the CHOK1SV® 10E9 cell line in conjunction with an improved, less fragmented CHOK1SV 10E9 genome assembly. Using our high‐resolution chromatin conformation datasets, we have assigned ≈90% of sequence to a chromosome‐scale genome assembly. Our genome‐wide 3D map identifies higher order chromatin structures such as topologically associated domains, incorporates our chromatin accessibility data to enhance the identification of active cis‐regulatory elements, and importantly links these cis‐regulatory elements to target promoters in a 3D promoter interactome. We demonstrate the power of our improved functional annotation by evaluating the 3D landscape of a transgene integration site and two phenotypically different cell lines. Our work opens up further novel genome engineering targets, has the potential to inform vital improvements for industrial biotherapeutic production, and represents a significant advancement for CHO cell line development.

Methylthioadenosine (MTA) boosts cell-specific productivities of Chinese hamster ovary cultures: dosage effects on proliferation, cell cycle and gene expression

A major goal for process and cell engineering in the biopharmaceutical industry is enhancing production through increasing volumetric and cell‐specific productivities (CSP). Here, we present 5′‐deoxy‐5′‐(methylthio)adenosine (MTA), the degradation product of S‐(5′‐adenosyl)‐L‐methionine (SAM), as a highly attractive native additive which can boost CSP by 79% when added to exponentially growing cells at a concentration of 250–300 μm. Notably, cell viability and cell size remain higher than in non‐treated cultures. In addition, cell cycle arrests first in S‐, then in G2‐phase before levelling out compared to non‐treated cultivations. Intensive differential gene analysis reveals that expression of genes for cytoskeleton mediated proteins and vesicle transport is amplified by treatment. Furthermore, the interaction of MTA with cell proliferation additionally stimulated recombinant protein formation. The results may serve as a promising starting point for further developments in process and cell engineering to boost productivity.

Chlorella vulgaris Extract as a Serum Replacement That Enhances Mammalian Cell Growth and Protein Expression

The global cell culture market is experiencing significant growth due to the rapid advancement in antibody-based and cell-based therapies. Both rely on the capacity of different living factories, namely prokaryotic and eukaryotic cells, plants or animals for reliable and mass production. The ability to improve production yield is of important concern. Among many strategies pursued, optimizing the complex nutritional requirements for cell growth and protein production has been frequently performed via culture media component titration and serum replacement. The addition of specific ingredients into culture media to modulate host cells’ metabolism has also recently been explored. In this study, we examined the use of extracted bioactive components of the microalgae Chlorella vulgaris, termed chlorella growth factor (CGF), as a cell culture additive for serum replacement and protein expression induction. We first established a chemical fingerprint of CGF using ultraviolet-visible spectroscopy and liquid chromatography-mass spectrometry and evaluated its ability to enhance cell proliferation in mammalian host cells. CGF successfully promoted the growth of Chinese hamster ovary (CHO) and mesenchymal stem cells (MSC), in both 2D and 3D cell cultures under reduced serum conditions for up to 21 days. In addition, CGF preserved cell functions as evident by an increase in protein expression in CHO cells and the maintenance of stem cell phenotype in MSC. Taken together, our results suggest that CGF is a viable culture media additive and growth matrix component, with wide ranging applications in biotechnology and tissue engineering.

Construction of an expression vector mediated by the dual promoter for prokaryotic and mammalian cell expression system

The aim of this study was to construct an expression vector mediated by the dual promoter that can simultaneously drive the recombinant protein production in eukaryotic and prokaryotic cells. The prokaryotic T7 promoter and ribosome binding site (RBS) was cloned downstream of CMV promoter in the eukaryotic expression vector pIRES-neo, and T7 termination sequence was inserted upstream of neomycin phosphotransferase gene to generate the dual promoter vector. The enhanced green fluorescent protein (eGFP) gene was used as reporter gene. Then, the resultant vector was transfected into Chinese hamster ovary (CHO) cells and transformed into Escherichia coli (E. coli) BL21, and the eGFP expression levels were analyzed by fluorescence microscopy, flow cytometry and Western blot, respectively. Fluorescence microscopy revealed that the eGFP was expressed in both CHO cells and E. coli BL21. Flow cytometry showed that the eGFP expression level had no significant difference between the dual promoter vector and control vector in transfected CHO cells. Western blot analysis indicated the eGFP expressed in transformed E. coli. In conclusion, a prokaryotic-eukaryotic double expression vector was successfully constructed, which has potential applications in rapid cloning and expression of recombinant proteins in both prokaryotic and eukaryotic expression systems.

Transient vitamin B5 starving improves mammalian cell homeostasis and protein production

Maintaining a metabolic steady state is essential for an organism's fitness and survival when confronted with environmental stress, and metabolic imbalance can be reversed by exposing the organism to fasting. Here, we attempted to apply this physiological principle to mammalian cell cultures to improve cellular fitness and consequently their ability to express recombinant proteins. We showed that transient vitamin B5 deprivation, an essential cofactor of central cellular metabolism, can quickly and irreversibly affect mammalian cell growth and division. A selection method was designed that relies on mammalian cell dependence on vitamin B5 for energy production, using the co-expression of the B5 transporter SLC5A6 and a gene of interest. We demonstrated that vitamin B5 selection persistently activates peroxisome proliferator-activated receptors (PPAR), a family of transcription factors involved in energy homeostasis, thereby altering lipid metabolism, improving cell fitness and therapeutic protein production. Thus, stable PPAR activation may constitute a cellular memory of past deprivation state, providing increased resistance to further potential fasting events. In other words, our results imply that cultured cells, once exposed to metabolic starvation, may display an improved metabolic fitness as compared to non-exposed cells, allowing increased resistance to cellular stress.

Overexpression of transcription factor Foxa1 and target genes remediate therapeutic protein production bottlenecks in Chinese hamster ovary cells

Despite extensive research conducted to increase protein production from Chinese hamster ovary (CHO) cells, cellular bottlenecks often remain, hindering high yields. In this study, a transcriptomic analysis led to the identification of 32 genes that are consistently upregulated in high producer clones and thus might mediate high productivity. Candidate genes were associated with functions such as signaling, protein folding, cytoskeleton organization, and cell survival. We focused on two engineering targets, Erp27, which binds unfolded proteins and the Erp57 disulfide isomerase in the endoplasmic reticulum, and Foxa1, a pioneering transcription factor involved in organ development. Erp27 moderate overexpression increased production of an easy-to-express antibody, whereas Erp27 and Erp57 co-overexpression increased cell density, viability, and the yield of difficult-to-express proteins. Foxa1 overexpression increased cell density, cell viability, and easy- and difficult-to-express protein yields, whereas it decreased reactive oxygen species late in fed-batch cultures. Foxa1 overexpression upregulated two other candidate genes that increased the production of difficult- and/or easy-to-express proteins, namely Ca3, involved in protecting cells from oxidative stress, and Tagap, involved in signaling and cytoskeleton remodeling. Overall, several genes allowing to overcome CHO cell bottlenecks were identified, including Foxa1, which mediated multiple favorable metabolic changes that improve therapeutic protein yields.

Influence of cytoskeleton organization on recombinant protein expression by CHO cells

In this study, we assessed the importance of cytoskeleton organization in the mammalian cells used to produce therapeutic proteins. Two cytoskeletal genes, Actin alpha cardiac muscle 1 (ACTC1) and a guanosine triphosphate GTPase-activating protein (TAGAP), were found to be upregulated in highly productive therapeutic protein-expressing Chinese hamster ovary (CHO) cells selected by the deprivation of vitamin B5. We report here that the overexpression of the ACTC1 protein was able to improve significantly recombinant therapeutic production, as well as to decrease the levels of toxic lactate metabolic by-products. ACTC1 overexpression was accompanied by altered as well as decreased polymerized actin, which was associated with high protein production by CHO cell cultured in suspension. We suggest that the depolymerization of actin and the possible modulation of integrin signaling, as well as changes in basal metabolism, may be driving the increase of protein secretion by CHO cells.