Cheng, H. C. | Search bioRxiv

bioRxiv2026

Sequential, Chromosome-Specific Glutamine Synthetase Double Knockout with Cas-CLOVER Establishes Enhanced CHO Platforms for Cell Line Development

Cas-CLOVER is an emerging high-fidelity genome editing system that enables precise and efficient cell engineering. In this study, we applied Cas-CLOVER to establish a robust, gene-edited platform in suspension-adapted CHO-K1 cells supporting cell line development (CLD) for biopharmaceutical production. An attractive strategy for high yield clone selection is the use of glutamine synthetase (GS) knockout CHO cells. The primary GS gene resides on chromosome 5 (GS5), while a recently identified GS pseudogene is located on chromosome 1 (GS1). To compare editing efficiency, we evaluated Cas-CLOVER and Cas9 at both GS loci using the Neon Transfection System. Cas-CLOVER achieved 84% editing at GS5 and 74% at GS1, markedly higher than Cas 9. Leveraging Cas-CLOVERs dual-guide RNA design, we generated a GS5 single knockout (GS5-SKO) and subsequently a double knockout (GS-DKO) line at both the GS5 and GS1 loci, both with none detected off-target mutations analyzed in 40 predictably off-target sites. For functional validation, these cell lines were engineered with the proprietary Harbor-IN transposase system to stably express trastuzumab. Using an optimized protocol, the resulting GS-DKO platform, termed CleanCut GS CHO, enabled stringent selection and yielded high-producing clones with cell-specific productivity exceeding 100 pg/cell/day and antibody titers greater than 5 g/L in 24 deep well-plate fed-batch cultures after 14 days. The antibody titer stability analysis showed consistency over 60 generations. Collectively, these findings establish Cas-CLOVER as a versatile genome editing tool for developing high-yield CHO host platforms in CLD.

bioengineering↗

bioRxiv2020

An Atlas of Phosphorylation and Proteolytic Processing Events During Excitotoxic Neuronal Death Reveals New Therapeutic Opportunities

Excitotoxicity, a neuronal death process in neurological disorders, is initiated by over-stimulation of neuronal ionotropic glutamate receptors. The over-stimulated receptors dysregulate proteases, protein kinases and phosphatases, which in turn modify target neuronal proteins to induce cell death. To decipher this cell death mechanism, we used quantitative proteomics, phosphoproteomics and N-terminomics to identify modified proteins in excitotoxic neurons. Data, available in ProteomeXchange (identifiers: PXD019527 and PXD019211), enabled us to identify over one thousand such proteins with calpains, cathepsins and over twenty protein kinases as their major modifiers. These protein modification events can potentially perturb signalling pathways governing cell survival, synaptogenesis, axonal guidance and mRNA processing. Importantly, blocking the modification of Src protein kinase, a signalling hub in excitotoxic neurons, protected against neuronal loss in vivo in a rat model of neurotoxicity. Besides offering new insights into excitotoxic neuronal death mechanism, our findings suggest potential neuroprotective therapeutic targets for treating neurological disorders. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=162 SRC="FIGDIR/small/151456v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@1f0191forg.highwire.dtl.DTLVardef@17ba2org.highwire.dtl.DTLVardef@15c0848org.highwire.dtl.DTLVardef@123d28b_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMulti-dimensional proteomic analysis identified proteins modified by proteolysis and altered phosphorylation in neurons undergoing excitotoxic cell death. C_LIO_LICalpains, cathepsins and over twenty protein kinases are major modifiers of these proteins. C_LIO_LIThese protein modification events are predicted to impact cell survival, axonal guidance, synaptogenesis and mRNA processing. C_LIO_LIBlocking modification of an identified protein Src, which acts as a major signalling hub in neurons, was protective against excitotoxic injury in vivo. C_LI In BriefUsing multidimensional proteomic approaches, Ameen, et al. mapped the changes of proteome, phosphoproteome and N-terminome of cultured primary neurons during excitotoxicity, a crucial neuronal death process in neurological disorders. These proteomic changes document new excitotoxicity-associated molecular events, and offer insights into how these events are organized to induce neuronal death. Potential therapeutic relevance of these molecular events is illustrated by the demonstration that in vivo blockade of one of these events could protect against excitotoxic neuronal loss.

biochemistry↗