Protein production from HEK293 cell line-derived stable pools with high protein quality and quantity to support discovery research

Antibody-based therapeutics and recombinant protein reagents are often produced in mammalian expression systems, which provide human-like post-translational modifications. Among the available mammalian cell lines used for recombinant protein expression, Chinese hamster ovary (CHO)-derived suspension cells are generally utilized because they are easy to culture and tend to produce proteins in high yield. However, some proteins purified from CHO cell overexpression suffer from clipping and display undesired non-human post translational modifications (PTMs). In addition, CHO cell lines are often not suitable for producing proteins with many glycosylation motifs for structural biology studies, as N-linked glycosylation of proteins poses challenges for structure determination by X-ray crystallography. Hence, alternative and complementary cell lines are required to address these issues. Here, we present a robust method for expressing proteins in human embryonic kidney 293 (HEK293)-derived stable pools, leading to recombinant protein products with much less clipped species compared to those expressed in CHO cells and with higher yield compared to those expressed in transiently-transfected HEK293 cells. Importantly, the stable pool generation protocol is also applicable to HEK293S GnTI- (N-acetylglucosaminyltransferase I-negative) and Expi293F GnTI- suspension cells, facilitating production of high yields of proteins with less complex glycans for use in structural biology projects. Compared to HEK293S GnTI- stable pools, Expi293F GnTI- stable pools consistently produce proteins with similar or higher expression levels. HEK293-derived stable pools can lead to a significant cost reduction and greatly promote the production of high-quality proteins for diverse research projects.

Immunotherapy combinations overcome resistance to bispecific T cell engager treatment in T cell-cold solid tumors

Therapeutic approaches are needed to promote T cell-mediated destruction of poorly immunogenic, "cold" tumors typically associated with minimal response to immune checkpoint blockade (ICB) therapy. Bispecific T cell engager (BiTE) molecules induce redirected lysis of cancer cells by polyclonal T cells and have demonstrated promising clinical activity against solid tumors in some patients. However, little is understood about the key factors that govern clinical responses to these therapies. Using an immunocompetent mouse model expressing a humanized CD3ε chain (huCD3e mice) and BiTE molecules directed against mouse CD19, mouse CLDN18.2, or human EPCAM antigens, we investigated the pharmacokinetic and pharmacodynamic parameters and immune correlates associated with BiTE efficacy across multiple syngeneic solid-tumor models. These studies demonstrated that pretreatment tumor-associated T cell density is a critical determinant of response to BiTE therapy, identified CD8⁺ T cells as important targets and mediators of BiTE activity, and revealed an antagonistic role for CD4⁺ T cells in BiTE efficacy. We also identified therapeutic combinations, including ICB and 4-1BB agonism, that synergized with BiTE treatment in poorly T cell-infiltrated, immunotherapy-refractory tumors. In these models, BiTE efficacy was dependent on local expansion of tumor-associated CD8⁺ T cells, rather than their recruitment from circulation. Our findings highlight the relative contributions of baseline T cell infiltration, local T cell proliferation, and peripheral T cell trafficking for BiTE molecule-mediated efficacy, identify combination strategies capable of overcoming resistance to BiTE therapy, and have clinical relevance for the development of BiTE and other T cell engager therapies.

Automated buffer preparation using quaternary valve in fast performance liquid chromatography for protein purification from a cell membrane

There is a great need for high-throughput protein purification to produce protein molecules for research and therapeutics. Although there have been significant advancements made in automated multi-step chromatography and preparative in-process design-of-experiment (DOE) capabilities in commercial fast performance liquid chromatography (FPLC) instruments, almost all commercial FPLCs rely on a binary buffer mixing system, which hinders automated buffer preparation. Nevertheless, current-generation FPLCs are equipped with a quaternary mixer designed for limited in-line buffer preparation and preparative pH scouting DOE experiments. We decided to leverage the quaternary mixing capability by extending and re-programming AkTA Avant's quaternary valve into an automated in-process buffer preparation system to simplify automated purification requiring complex washing steps. We accomplished this by using two extra inlet valves, a sample valve, and versatile valve to split inputs of the quaternary valve into software-selectable stock solutions of pH buffers, salts, eluents, and additives. We also devised a new flow scheme to perform automated two-step chromatography using only one versatile valve. This was accomplished by using only stock parts and software to facilitate reproduction. To demonstrate the versatility and capability of the system, we purified a transmembrane protein that requires a detergent to stay soluble and needs an in-column, high-salt washing step to achieve high purity.

Membrane cholesterol modulates STEAP2 conformation during dynamic intracellular trafficking processes leading to broad subcellular distribution

STEAP2 is a member of the Six-Transmembrane Epithelial Antigen of the Prostate (STEAP) protein family that is proposed to function as metalloreductase. While STEAP2 shows a complex subcellular distribution pattern localizing to both secretory and endocytic pathway organelles, how such broad steady-state distribution is maintained is unknown. Similarly, whether STEAP2 undergoes any compartment-specific modulation during intracellular trafficking has not been reported. Leveraging a newly-identified monoclonal antibody that recognizes a conformation-sensitive epitope nested in the second extracellular loop of STEAP2, we demonstrate that the epitope formation was dependent on the cholesterol content of the membrane in which STEAP2 was embedded. Monitoring the STEAP2-dependent internalization of this antibody uncovered STEAP2's rapid internalization from the cell surface and their subsequence trafficking to the Golgi region and endosome-like puncta. Acute inhibition of endocytosis also increased the detectable amount of STEAP2 at the plasma membrane. Collectively, these experiments demonstrate that an intricate balance of membrane flux between the secretory and endocytic pathways underlies the characteristic broad subcellular localization of STEAP2. By using a cell-based assay that detects the metalloreductase functions of cell surface-localizing STEAP4, STEAP2's metalloreductase activities were not detectable, suggesting that its enzymatic function is suppressed at the plasma membrane. The conformational modulation of STEAP2 by the local membrane cholesterol content can therefore serve as a potential mechanism to modulate STEAP2 function in a compartment-restricted manner, by coupling a pre-existing difference in cholesterol content among different cellular membranes to a dynamic trafficking process leading to broad subcellular distribution.

Novel protein therapeutic joint retention strategy based on collagen-binding Avimers

Designing drugs to treat diseases associated with articular joints, particularly those targeting chondrocytes, is challenging due to unique local environmental constraints including the avascular nature of cartilage, the absence of a closed joint compartment, and a highly cross-linked extracellular matrix. In an effort to address these challenges, we developed a novel strategy to prolong residence time of intra-articularly administered protein therapeutics. Avimer domains are naturally found in membrane polypeptides and mediate diverse protein-protein interactions. Screening of a phage Avimer domain library led to identification of several low affinity type II collagen-binding Avimers. Following several rounds of mutagenesis and reselection, these initial hits were transformed to high affinity, selective type II collagen-binding Avimers. One such Avimer (M26) persisted in rat knees for at least 1 month following intra-articular administration. Fusion of this Avimer to a candidate therapeutic payload, IL-1Ra, yielded a protein construct which simultaneously bound to type II collagen and to IL-1 receptor. In vitro, IL-1Ra_M26 bound selectively to cartilage explants and remained associated even after extensive washing. Binding appeared to occur preferentially to pericellular regions surrounding chondrocytes. An acute intra-articular IL-1-induced IL-6 challenge rat model was employed to assess in vivo pharmacodynamics. Whereas both IL-1Ra_M26 and native IL-1Ra inhibited IL-6 output when co-administered with the IL-1 challenge, only IL-1Ra_M26 inhibited when administered 1 week prior to IL-1 challenge. Collagen-binding Avimers thus represent a promising strategy for enhancing cartilage residence time of protein therapeutics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1238-1247, 2018.

FGF21 can be mimicked in vitro and in vivo by a novel anti-FGFR1c/β-Klotho bispecific protein

The endocrine hormone FGF21 has attracted considerable interest as a potential therapeutic for treating diabetes and obesity. As an alternative to the native cytokine, we generated bispecific Avimer polypeptides that bind with high affinity and specificity to one of the receptor and coreceptor pairs used by FGF21, FGFR1c and β-Klotho. These Avimers exhibit FGF21-like activity in in vitro assays with potency greater than FGF21. In a study conducted in obese male cynomolgus monkeys, animals treated with an FGFR1c/β-Klotho bispecific Avimer showed improved metabolic parameters and reduced body weight comparable to the effects seen with FGF21. These results not only demonstrate the essential roles of FGFR1c and β-Klotho in mediating the metabolic effects of FGF21, they also describe a first bispecific activator of this unique receptor complex and provide validation for a novel therapeutic approach to target this potentially important pathway for treating diabetes and obesity.

Fine-tuning of the Escherichia coli sigmaE envelope stress response relies on multiple mechanisms to inhibit signal-independent proteolysis of the transmembrane anti-sigma factor, RseA

Proteolytic cascades are widely implicated in signaling between cellular compartments. In Escherichia coli, accumulation of unassembled outer membrane porins (OMPs) in the envelope leads to expression of sigma(E)-dependent genes in the cytoplasmic cellular compartment. A proteolytic cascade conveys the OMP signal by regulated proteolysis of RseA, a membrane-spanning anti-sigma factor whose cytoplasmic domain inhibits sigma(E)-dependent transcription. Upon activation by OMP C termini, the membrane localized DegS protease cleaves RseA in its periplasmic domain, the membrane-embedded protease RseP (YaeL) cleaves RseA near the inner membrane, and the released cytoplasmic RseA fragment is further degraded. Initiation of RseA degradation by activated DegS makes the system sensitive to a wide range of OMP concentrations and unresponsive to variations in the levels of DegS and RseP proteases. These features rely on the inability of RseP to cleave intact RseA. In the present report, we demonstrate that RseB, which binds to the periplasmic face of RseA, and DegS each independently inhibits RseP cleavage of intact RseA. Thus, the function of RseB, widely conserved among bacteria using the sigma(E) pathway, and the second role of DegS (in addition to RseA proteolysis initiation) is to improve the performance characteristics of this signal transduction system.

Regulation of the Escherichia coli sigma-dependent envelope stress response

The Escherichia colisigma(E)-dependent stress response pathway controls the expression of genes encoding periplasmic folding catalysts, proteases, biosynthesis enzymes for lipid A (a component of lipopolysaccharide or LPS) and other proteins known or predicted to function in or produce components of the envelope. When E. coli is subjected to heat or other stresses that generate unfolded envelope proteins, sigma(E) activity is induced. Four key players in this signal transduction pathway have been identified: RseA, an inner membrane sigma(E) antisigma factor; RseB, a periplasmic protein that binds to the periplasmic face of RseA; and the DegS and YaeL proteases. The major point of regulation, the interaction between sigma(E) and RseA, is primarily controlled by the stability of RseA. Envelope stress promotes RseA degradation, which occurs by a proteolytic cascade initiated by DegS. There is evidence that one sigma(E)-inducing stress (OmpC overexpression) directly activates DegS to cleave RseA. Secondarily, envelope stress may relieve RseB-mediated enhancement of RseA activity. Additional levels of control upon sigma(E) activity may become evident upon further study of this stress response pathway.

OMP peptide signals initiate the envelope-stress response by activating DegS protease via relief of inhibition mediated by its PDZ domain

Transmembrane signaling between intracellular compartments is often controlled by regulated proteolysis. Escherichia coli respond to misfolded or unfolded outer-membrane porins (OMPs) in the periplasm by inducing sigma(E)-dependent transcription of stress genes in the cytoplasm. This process requires a proteolytic cascade initiated by the DegS protease, which destroys a transmembrane protein (RseA) that normally binds to and inhibits sigma(E). Here, we show that peptides ending with OMP-like C-terminal sequences bind the DegS PDZ domain, activate DegS cleavage of RseA, and induce sigma(E)-dependent transcription. These results suggest that DegS acts as a sensor of envelope stress by binding unassembled OMPs. DegS activation involves relief of inhibitory interactions between its PDZ and protease domains. Peptide binding to inhibitory PDZ domains in proteases related to DegS, including DegP/HtrA, may also regulate the degradation of specific substrates by these enzymes.

DegS and YaeL participate sequentially in the cleavage of RseA to activate the sigma(E)-dependent extracytoplasmic stress response

All cells have stress response pathways that maintain homeostasis in each cellular compartment. In the Gram-negative bacterium Escherichia coli, the sigma(E) pathway responds to protein misfolding in the envelope. The stress signal is transduced across the inner membrane to the cytoplasm via the inner membrane protein RseA, the anti-sigma factor that inhibits the transcriptional activity of sigma(E). Stress-induced activation of the pathway requires the regulated proteolysis of RseA. In this report we show that RseA is degraded by sequential proteolytic events controlled by the inner membrane-anchored protease DegS and the membrane-embedded metalloprotease YaeL, an ortholog of mammalian Site-2 protease (S2P). This is consistent with the mechanism of activation of ATF6, the mammalian unfolded protein response transcription factor by Site-1 protease and S2P. Thus, mammalian and bacterial cells employ a conserved proteolytic mechanism to activate membrane-associated transcription factors that initiate intercompartmental cellular stress responses.

degS (hhoB) is an essential Escherichia coli gene whose indispensable function is to provide sigma (E) activity

DegS (HhoB), a putative serine protease related to DegP/HtrA, regulates the basal and induced activity of the essential Escherichia coli sigma factor sigma (E), which is involved in the cellular response to extracytoplasmic stress. DegS promotes the destabilization of the sigma (E)-specific anti-sigma factor RseA, thereby releasing sigma (E) to direct gene expression. We demonstrate that degS is an essential E. coli gene and show that the essential function of DegS is to provide the cell with sigma (E) activity. We also show that the putative active site of DegS is periplasmic and that DegS requires its N-terminal transmembrane domain for its sigma (E)-related function.

The Escherichia coli sigma(E)-dependent extracytoplasmic stress response is controlled by the regulated proteolysis of an anti-sigma factor

The activity of the stress-responsive sigma factor, sigma(E), is induced by the extracytoplasmic accumulation of misfolded or unfolded protein. The inner membrane protein RseA is the central regulatory molecule in this signal transduction cascade and acts as a sigma(E)-specific anti-sigma factor. Here we show that sigma(E) activity is primarily determined by the ratio of RseA to sigma(E). RseA is rapidly degraded in response to extracytoplasmic stress, leading to an increase in the free pool of sigma(E) and initiation of the stress response. We present evidence that the putative inner membrane serine protease, DegS, is responsible for this regulated degradation of RseA.

The response to extracytoplasmic stress in Escherichia coli is controlled by partially overlapping pathways

The activity of the alternate sigma-factor sigmaE of Escherichia coli is induced by several stressors that lead to the extracytoplasmic accumulation of misfolded or unfolded protein. The sigmaE regulon contains several genes, including that encoding the periplasmic protease DegP, whose products are thought to be required for maintaining the integrity of the cell envelope because cells lacking sigmaE are sensitive to elevated temperature and hydrophobic agents. Selection of multicopy suppressors of the temperature-sensitive phenotype of cells lacking sigmaE revealed that overexpression of the lipoprotein NlpE restored high temperature growth to these cells. Overexpression of NlpE has been shown previously to induce DegP synthesis by activating the Cpx two-component signal transduction pathway, and suppression of the temperature-sensitive phenotype by NlpE was found to be dependent on the Cpx proteins. In addition, a constitutively active form of the CpxA sensor/kinase also fully suppressed the temperature-sensitive defect of cells lacking sigmaE. DegP was found to be necessary, but not sufficient, for suppression. Activation of the Cpx pathway has also been shown to alleviate the toxicity of several LamB mutant proteins. Together, these results reveal the existence of two partially overlapping regulatory systems involved in the response to extracytoplasmic stress in E. coli.

Effects of approximation on postural sway in healthy subjects

The effect of approximation on the postural sway of healthy subjects wearing a weighted belt around their pelvis was measured. Twenty subjects between the ages of 23 and 30 years stood on a polyurethane foam platform that amplified their postural sway and were filmed from a lateral view. All subjects wore markers over their mandibles, hips, and knees and were filmed three times with the weighted belt worn on a randomly selected trial. Frames from a 10-second interval of film from each trial were studied, and the summed displacement at each bony landmark between each frame of film was calculated. A significant decrease in displacement at the mandible (p less than .02) was found when the weighted belt was worn. The decrease in displacement was not significant at the hip or knee. Approximation was shown to decrease the postural sway of healthy subjects. Further study is indicated to investigate the effect of approximation on patient populations.