Polysome profiling of mAb producing CHO cell lines links translational control of cell proliferation and recombinant mRNA loading onto ribosomes with global and recombinant protein synthesis.

mRNA translation is a key process determining growth, proliferation and duration of a Chinese hamster ovary (CHO) cell culture and influences recombinant protein synthesis rate. During bioprocessing, CHO cells can experience stresses leading to reprogramming of translation and decreased global protein synthesis. Here we apply polysome profiling to determine reprogramming and translational capabilities in host and recombinant monoclonal antibody-producing (mAb) CHO cell lines during batch culture. Recombinant cell lines with the fastest cell specific growth rates were those with the highest global translational efficiency. However, total ribosomal capacity, determined from polysome profiles, did not relate to the fastest growing or highest producing mAb cell line, suggesting it is the ability to utilise available machinery that determines protein synthetic capacity. Cell lines with higher cell specific productivities tended to have elevated recombinant heavy chain transcript copy numbers, localised to the translationally active heavy polysomes. The highest titre cell line was that which sustained recombinant protein synthesis and maintained high recombinant transcript copy numbers in polysomes. Investigation of specific endogenous transcripts revealed a number that maintained or reprogrammed into heavy polysomes, identifying targets for potential cell engineering or those with 5' untranslated regions that might be utilised to enhance recombinant transcript translation.

The structure of MSK1 reveals a novel autoinhibitory conformation for a dual kinase protein.

Mitogen and stress-activated kinase-1 (MSK1) is a serine/threonine protein kinase that is activated by either p38 or p42ERK MAPKs in response to stress or mitogenic extracellular stimuli. MSK1 belongs to a family of protein kinases that contain two distinct kinase domains in one polypeptide chain. We report the 1.8 A crystal structure of the N-terminal kinase domain of MSK1. The crystal structure reveals a unique inactive conformation with the ATP binding site blocked by the nucleotide binding loop. This inactive conformation is stabilized by the formation of a new three-stranded beta sheet on the N lobe of the kinase domain. The three beta strands come from residues at the N terminus of the kinase domain, what would be the alphaB helix in the active conformation, and the activation loop. The new three-stranded beta sheet occupies a position equivalent to the N terminus of the alphaC helix in active protein kinases.

Discovery of GSK2795039, a Novel Small Molecule NADPH Oxidase 2 Inhibitor.

AIMS: The NADPH oxidase (NOX) family of enzymes catalyzes the formation of reactive oxygen species (ROS). NOX enzymes not only have a key role in a variety of physiological processes but also contribute to oxidative stress in certain disease states. To date, while numerous small molecule inhibitors have been reported (in particular for NOX2), none have demonstrated inhibitory activity in vivo. As such, there is a need for the identification of improved NOX inhibitors to enable further evaluation of the biological functions of NOX enzymes in vivo as well as the therapeutic potential of NOX inhibition. In this study, both the in vitro and in vivo pharmacological profiles of GSK2795039, a novel NOX2 inhibitor, were characterized in comparison with other published NOX inhibitors. RESULTS: GSK2795039 inhibited both the formation of ROS and the utilization of the enzyme substrates, NADPH and oxygen, in a variety of semirecombinant cell-free and cell-based NOX2 assays. It inhibited NOX2 in an NADPH competitive manner and was selective over other NOX isoforms, xanthine oxidase, and endothelial nitric oxide synthase enzymes. Following systemic administration in mice, GSK2795039 abolished the production of ROS by activated NOX2 enzyme in a paw inflammation model. Furthermore, GSK2795039 showed activity in a murine model of acute pancreatitis, reducing the levels of serum amylase triggered by systemic injection of cerulein. INNOVATION AND CONCLUSIONS: GSK2795039 is a novel NOX2 inhibitor that is the first small molecule to demonstrate inhibition of the NOX2 enzyme in vivo.

A high-yielding CHO transient system: coexpression of genes encoding EBNA-1 and GS enhances transient protein expression.

An efficient rapid protein expression system is crucial to support early drug development. Transient gene expression is an effective route, and to facilitate the use of the same host cells as for subsequent stable cell line development, we have created a high-yielding Chinese hamster ovary (CHO) transient expression system. Suspension-adapted CHO-K1 host cells were engineered to express the gene encoding Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA-1) with and without the coexpression of the gene for glutamine synthetase (GS). Analysis of the transfectants indicated that coexpression of EBNA-1 and GS enhanced transient expression of a recombinant antibody from a plasmid carrying an OriP DNA element compared to EBNA-1-only transfectants. This was confirmed with the retransfection of an EBNA-1-only cell line with a GS gene. The retransfected cell lines showed an increase in transient expression when compared with that of the EBNA-1-only parent. The transient expression process for the best CHO transient cell line was further developed to enhance protein expression and improve scalability by optimizing the transfection conditions and the cell culture process. This resulted in a scalable CHO transient expression system that is capable of expressing 2 g/L of recombinant proteins such as antibodies. This system can now rapidly provide gram amounts of recombinant antibody to supply preclinical development studies that has comparable product quality to antibody produced from a stably transfected CHO cell line.

Expression and purification of functional JNK2beta2: perspectives on high-level production of recombinant MAP kinases.

The mitogen-activated protein (MAP) kinases are a group of serine/threonine kinases that mediate intracellular signal transduction in response to environmental stimuli including stress, growth factors, and various cytokines. Of this family, the c-Jun N-terminal kinases (JNKs) are members which, depending on cell type, have been shown to activate the transcription of genes involved in the inflammatory response, apoptosis, and hypertrophy. Here we report the use Baculovirus/Sf9 cells to produce milligram quantities of recombinant JNK2beta2 substrate which could be purified to >90% as judged by SDS-PAGE. In addition, we report a novel method for the site-specific biotinylation for this enzyme and demonstrate that the biotinylated product is an authentic substrate of the upstream kinases MKK4 and 7 and can phosphorylate a downstream target, ATF-2. We also show that the phosphorylated product can be captured efficiently on streptavidin-coated beads for use in scintillation proximity assays.