Understanding translational control mechanisms of the mTOR pathway in CHO cells by polysome profiling

Ectoine enhances recombinant antibody production in Chinese hamster ovary cells by promoting cell cycle arrest

Chinese hamster ovary (CHO) cells represent the most preferential host cell system for therapeutic monoclonal antibody (mAb) production. Enhancing mAb production in CHO cells can be achieved by adding chemical compounds that regulate the cell cycle and cell survival pathways. This study investigated the impact of ectoine supplementation on mAb production in CHO cells. The results showed that adding ectoine at a concentration of 100 mM on the 3rd day of cultivation improved mAb production by improving cell viability and extending the culture duration. RNA sequencing analysis revealed differentially expressed genes associated with cell cycle regulation, cell proliferation, and cellular homeostasis, in particular promotion of cell cycle arrest, which was then confirmed by flow cytometry analysis. Ectoine-treated CHO cells exhibited an increase in the number of cells in the G0/G1 phase. In addition, the cell diameter was also increased. These findings support the hypothesis that ectoine enhances mAb production in CHO cells through mechanisms involving cell cycle arrest and cellular homeostasis. Overall, this study highlights the potential of ectoine as a promising supplementation strategy to enhance mAb production not only in CHO cells but also in other cell lines.

Improving recombinant protein production in CHO cells using the CRISPR-Cas system

Chinese hamster ovary (CHO) cells are among the most widely used mammalian cell lines in the biopharmaceutical industry. Therefore, it is not surprising that significant efforts have been made around the engineering of CHO cells using genetic engineering methods such as the CRISPR-Cas system. In this review, we summarize key recent studies that have used different CRISPR-Cas systems such as Cas9, Cas13 or dCas9 fused with effector domains to improve recombinant protein (r-protein) production in CHO cells. Here, every relevant stage of production was considered, underscoring the advantages and limitations of these systems, as well as discussing their bottlenecks and probable solutions. A special emphasis was given on how these systems could disrupt and/or regulate genes related to glycan composition, which has relevant effects over r-protein properties and in vivo activity. Furthermore, the related promising future applications of CRISPR to achieve a tunable, reversible, or highly stable editing of CHO cells are discussed. Overall, the studies covered in this review show that despite the complexity of mammalian cells, the synthetic biology community has developed many mature strategies to improve r-protein production using CHO cells. In this regard, CRISPR-Cas technology clearly provides efficient and flexible genetic manipulation and allows for the generation of more productive CHO cell lines, leading to more cost-efficient production of biopharmaceuticals, however, there is still a need for many emerging techniques in CRISPR to be reported in CHO cells; therefore, more research in these cells is needed to realize the full potential of this technology.

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.

Increased MSX level improves biological productivity and production stability in multiple recombinant GS CHO cell lines

Increasing cell culture productivity of recombinant proteins via process improvements is the primary focus for research groups within biologics manufacturing. Any recommendations to improve a manufacturing process obviously must be effective, but also be robust, scalable, and with product quality comparable to the original process. In this study, we report that three different GS-/- CHO cell lines developed in media containing a standard concentration of the selection agent methionine sulfoximine (MSX), but then exposed to increased MSX concentrations during seed train expansion, achieved titer increases of 10-19%. This result was observed in processes already considerably optimized. Expanding the cells with a higher MSX concentration improved cell line production stability with increased culture age. Production cultures in 500-L and 1000-L bioreactors replicated laboratory results using 5-L bioreactors, demonstrating process robustness and scalability. Furthermore, product quality attributes of the final drug substance using the higher MSX process were comparable with those from cells expanded in media with the standard selection MSX concentration. Subsequent mechanistic investigations confirmed that the cells were not altered at the genetic level in terms of integration profiles or gene copy number, nor transcriptional levels of glutamine synthetase, heavy chain, or light chain genes. This study provides an effective and applicable strategy to improve the productivity of therapeutic proteins for biologics manufacturing.

Cell cycle genes are downregulated after adipogenic triggering in human adipose tissue-derived stem cells by regulation of mRNA abundance

The adipogenic process is characterized by the expression of adipocyte differentiation markers that lead to changes in cell metabolism and to the accumulation of lipid droplets. Moreover, during early adipogenesis, cells undergo a strong downregulation of translational activity with a decrease in cell size, proliferation and migration. In the present study, we identified that after 24 hours of adipogenic induction, human adipose tissue-derived stem cells (hASCs) undergo a G1-cell cycle arrest consistent with reduced proliferation, and this effect was correlated with a shift in polysome profile with an enrichment of the monosomal fraction and a reduction of the polysomal fraction. Polysome profiling analysis also revealed that this change in the monosomal/polysomal ratio was related to a strong downregulation of cell cycle and proliferation genes, such as cyclins and cyclin-dependent kinases (CDKs). Comparing total and polysome-associated mRNA sequencing, we also observed that this downregulation was mostly due to a reduction of cell cycle and proliferation transcripts via control of total mRNA abundance, rather than by translational control.

Restricting the induction of NGF in ovarian stroma engenders selective follicular activation through the mTOR signaling pathway

In mammalian ovaries, primordial follicles remain in a quiescent state until activation by the surrounding microenvironment. Ovarian intervention, for example, ovarian cystectomy, ovarian wedge resection or laser drilling therapies for polycystic ovarian syndrome, has long been reported to change follicular development by an unknown mechanism(s). Herein, we established a murine model with partial ovarian resection of one ovary unilaterally, with the contralateral ovary undamaged. We found the injury accelerated follicular activation and development through the mTORC1 signaling pathway. Moreover, the stimulation of primordial follicles was restricted near the incision site where the mTORC1 pathway showed sequential activation beginning at the interstitial cells and proceeding to the primordial follicles. Total and polysome-associated RNA-seq revealed the increase of the nerve growth factor (NGF) family member, in both two fractions and immunostaining showed the restricted induction of NGF near the incision site. In cultured newborn ovaries, NGF demonstrated increase of follicular activation, and moreover, the NGF inhibitor K252a effectively blocked activation of primordial follicles stimulated by the surgery. We liken ovulation in mammals to minor tissue trauma, which happens naturally and cyclically in the body. As the increase in NGF accompanied the accumulation of activated primordial follicles after ovulation, our study may represent a common mechanism for selective follicular activation induced by a localized increase in NGF in interstitial cells and mediated via the mTOR signaling pathway. In addition, the NGF inhibitor K252a and the mTOR inhibitor rapamycin constitute good candidates for protecting follicular reserve against over exhaustion after ovarian surgery.

Ribosome profiling-guided depletion of an mRNA increases cell growth rate and protein secretion

Recombinant protein production coopts the host cell machinery to provide high protein yields of industrial enzymes or biotherapeutics. However, since protein translation is energetically expensive and tightly controlled, it is unclear if highly expressed recombinant genes are translated as efficiently as host genes. Furthermore, it is unclear how the high expression impacts global translation. Here, we present the first genome-wide view of protein translation in an IgG-producing CHO cell line, measured with ribosome profiling. Through this we found that our recombinant mRNAs were translated as efficiently as the host cell transcriptome, and sequestered up to 15% of the total ribosome occupancy. During cell culture, changes in recombinant mRNA translation were consistent with changes in transcription, demonstrating that transcript levels influence specific productivity. Using this information, we identified the unnecessary resistance marker NeoR to be a highly transcribed and translated gene. Through siRNA knock-down of NeoR, we improved the production- and growth capacity of the host cell. Thus, ribosomal profiling provides valuable insights into translation in CHO cells and can guide efforts to enhance protein production.

Stabilization of cellular mitochondrial enzyme complex and sialyltransferase activity through supplementation of 30Kc19 protein

In previous studies, 30Kc19, a lipoprotein in silkworm hemolymph, enhanced productivity and glycosylation by expression of a 30Kc19 gene or supplementation with a recombinant 30Kc19 protein. Additionally, 30Kc19 exhibited enzyme-stabilizing and cell-penetrating abilities in vitro. In this study, we hypothesized that supplemented 30Kc19 penetrated into the cell and enhanced the stability of the cellular enzyme. We investigated this using in vitro and cellular assessments. The activity of sialyltransferase (ST) and isolated mitochondrial complex I/III was enhanced with 30Kc19 in dose-dependent manner while initial reaction rate was unchanged, suggesting that 30Kc19 enhanced enzyme stability rather than specific activity. For intracellular enzyme activity assessment, ST activity inside erythropoietin (EPO)-producing Chinese hamster ovary (CHO) cells increased more than 25 % and mitochondrial complex II activity in HeLa cells increased more than 50 % with 30Kc19. The increase in intracellular ST activity resulted in an increase in sialic acid content of glycoproteins produced in CHO cells supplemented with 30Kc19. Similarly, enhanced mitochondrial complex activity increased mitochondrial membrane potential and ATP production in HeLa cells with 30Kc19 by over 50 %. Because 30Kc19 stabilized intracellular enzymes for glycosylation and enhanced protein productivity with supplementation in the culture medium, we expect that 30Kc19 can be a valuable tool for effective industrial recombinant protein production.

Fingerprints of a message: integrating positional information on the transcriptome

The recent explosion of high-throughput sequencing methods applied to RNA molecules is allowing us to go beyond the description of sequence variants and their relative abundances, as measured by RNA-seq. We can now probe for RNA engagement in polysomes, for ribosomes, RNA binding proteins and microRNAs binding sites, for RNA secondary structure and for RNA methylation. These descriptors produce a steadily growing multidimensional array of positional information on RNA sequences, whose effective integration only would bring to decipher the regulatory interplay occurring between proteins, RNAs and their modifications on the transcriptome. This interplay ultimately dictates the degree of mRNA availability to translation, and thus the occurrence of cell phenotypes. However, several issues in data presentation are slowing down effective integration. A standardization effort for new dataset types produced should be urgently undertaken to solve these issues. Providing uniformed experimental details along with datasets processed to be directly usable and employing shared formats would greatly simplify integration efforts, strengthening hypotheses stemming from correlative observations and eventually bringing to mechanistic understanding.

28S rRNA is inducibly pseudouridylated by the mTOR pathway translational control in CHO cell cultures

The mTOR pathway is a conserved master regulator of translational activity that influences the fate of industrially relevant CHO cell cultures, yet its molecular mechanisms remain unclear. Interestingly, rapamycin specific inhibition of the mTOR pathway in CHO cells was found to down-regulate the small nucleolar RNA U19 (snoRNA U19) by 2-fold via translatome profiling. snoRNA U19 guides the two most conserved pseudouridylation modifications on 28S ribosomal RNA (rRNA) that are important for the biogenesis and proper function of ribosomes. In order to further understand the role of snoRNA U19 as a potential player in the mTOR pathway, we measured 28S rRNA pseudouridylation upon rapamycin treatments and/or snoRNA U19 overexpression conditions, thereby characterizing the subsequent effects on ribosome efficiency and global translation by polysome profiling. We showed that 28S rRNA pseudouridylation was increased by rapamycin treatment and/or overexpression of snoRNA U19, but only the latter condition improved ribosome efficiency toward higher global translation, thus implying that the mTOR pathway induces pseudouridylation at different sites along the 28S rRNA possibly with either positive or negative effects on the cellular phenotype. This discovery of snoRNA U19 as a new downstream effector of the mTOR pathway suggests that cell engineering of snoRNAs can be used to regulate translation and improve cellular growth in CHO cell cultures in the future.