Rpl24Bst mutation suppresses colorectal cancer by promoting eEF2 phosphorylation via eEF2K.

Increased protein synthesis supports the rapid cell proliferation associated with cancer. The Rpl24Bst mutant mouse reduces the expression of the ribosomal protein RPL24 and has been used to suppress translation and limit tumorigenesis in multiple mouse models of cancer. Here, we show that Rpl24Bst also suppresses tumorigenesis and proliferation in a model of colorectal cancer (CRC) with two common patient mutations, Apc and Kras. In contrast to previous reports, Rpl24Bst mutation has no effect on ribosomal subunit abundance but suppresses translation elongation through phosphorylation of eEF2, reducing protein synthesis by 40% in tumour cells. Ablating eEF2 phosphorylation in Rpl24Bst mutant mice by inactivating its kinase, eEF2K, completely restores the rates of elongation and protein synthesis. Furthermore, eEF2K activity is required for the Rpl24Bst mutant to suppress tumorigenesis. This work demonstrates that elevation of eEF2 phosphorylation is an effective means to suppress colorectal tumorigenesis with two driver mutations. This positions translation elongation as a therapeutic target in CRC, as well as in other cancers where the Rpl24Bst mutation has a tumour suppressive effect in mouse models.

Engineering of Chinese Hamster Ovary Cells With NDPK-A to Enhance DNA Nuclear Delivery Combined With EBNA1 Plasmid Maintenance Gives Improved Exogenous Transient Reporter, mAb and SARS-CoV-2 Spike Protein Expression.

Transient gene expression (TGE) in mammalian cells is a method of rapidly generating recombinant protein material for initial characterisation studies that does not require time-consuming processes associated with stable cell line construction. High TGE yields are heavily dependent on efficient delivery of plasmid DNA across both the plasma and nuclear membranes. Here, we harness the protein nucleoside diphosphate kinase (NDPK-A) that contains a nuclear localisation signal (NLS) to enhance DNA delivery into the nucleus of CHO cells. We show that co-expression of NDPK-A during transient expression results in improved transfection efficiency in CHO cells, presumably due to enhanced transportation of plasmid DNA into the nucleus via the nuclear pore complex. Furthermore, introduction of the Epstein Barr Nuclear Antigen-1 (EBNA-1), a protein that is capable of inducing extrachromosomal maintenance, when coupled with complementary oriP elements on a transient plasmid, was utilised to reduce the effect of plasmid dilution. Whilst there was attenuated growth upon introduction of the EBNA-1 system into CHO cells, when both NDPK-A nuclear import and EBNA-1 mediated technologies were employed together this resulted in enhanced transient recombinant protein yields superior to those generated using either approach independently, including when expressing the complex SARS-CoV-2 spike (S) glycoprotein.

Application of microRNA Targeted 3'UTRs to Repress DHFR Selection Marker Expression for Development of Recombinant Antibody Expressing CHO Cell Pools.

The dihydrofolate reductase (DHFR) system is used for the selection of recombinant Chinese hamster ovary (CHO) cell lines using the inhibitor methotrexate (MTX). During clonal selection, endogenous DHFR expression, and resistance to MTX allows the selection of cells expressing sufficient DHFR to survive. Here, the authors describe a novel vector platform for the DHFR system, whereby addition of a synthetic 3'UTR destabilizes DHFR expression. miRs ability to negatively regulate gene expression by their near-complementary binding to the 3'UTR region of transcripts are harnessed. From the literature, the authors identified let-7f as a highly abundant, invariant miR in CHO cells. Three 3'UTR targets of the let-7f miR are then cloned in the DHFR host 3'UTR to determine the impact on gene expression (HMGA2 3'UTR sequence 1, 2, and 3). Using luciferase as a reporter, the authors show down-regulation of luciferase activity is mediated by the nature of the 3'UTR and its ability to bind let-7f. The same 3'UTRs downstream of the DHFR gene to show this also results in reduced transcript amounts are then applied. Finally, the authors applied this methodology to generate stable DG44-derived cell pools expressing a model monoclonal antibody (mAb), demonstrating this approach can be used for the selection of antibody-producing cells with low MTX concentrations.

Meta-Analysis of Publicly Available Chinese Hamster Ovary (CHO) Cell Transcriptomic Datasets for Identifying Engineering Targets to Enhance Recombinant Protein Yields.

Transcriptomics has been extensively applied to the investigation of the CHO cell platform for the production of recombinant biotherapeutic proteins to identify transcripts whose expression is regulated and correlated to (non)desirable CHO cell attributes. However, there have been few attempts to analyze the findings across these studies to identify conserved changes and generic targets for CHO cell platform engineering. Here, the authors have undertaken a meta-analysis of CHO cell transcriptomic data and report on those genes most frequently identified as differentially expressed with regard to cell growth (µ) and productivity (Qp). By aggregating differentially expressed genes from publicly available transcriptomic datasets associated with µ and Qp, using a pathway enrichment analysis and combining it with the concordance of gene expression values, the authors have identified a refined target gene and pathway list while determining the overlap across CHO transcriptomic studies. The authors find that only the cell cycle and lysosome pathways show good concordance. By mapping out the contributing genes the authors have constructed a transcriptomic "fingerprint" of a high-performing cell line. This study provides a starting resource for researchers who want to navigate the complex landscape of CHO transcriptomics and identify targets to undertake cell engineering for improved recombinant protein output.

The Long Non-Coding RNA Transcriptome Landscape in CHO Cells Under Batch and Fed-Batch Conditions.

The role of non-coding RNAs in determining growth, productivity, and recombinant product quality attributes in Chinese hamster ovary (CHO) cells has received much attention in recent years, exemplified by studies into microRNAs in particular. However, other classes of non-coding RNAs have received less attention. One such class are the non-coding RNAs known collectively as long non-coding RNAs (lncRNAs). The authors have undertaken the first landscape analysis of the lncRNA transcriptome in CHO using a mouse based microarray that also provided for the surveillance of the coding transcriptome. The authors report on those lncRNAs present in a model host CHO cell line under batch and fed-batch conditions on two different days and relate the expression of different lncRNAs to each other. The authors demonstrate that the mouse microarray is suitable for the detection and analysis of thousands of CHO lncRNAs and validated a number of these by qRT-PCR. The authors then further analyzed the data to identify those lncRNAs whose expression changed the most between growth and stationary phases of culture or between batch and fed-batch culture to identify potential lncRNA targets for further functional studies with regard to their role in controlling growth of CHO cells. The authors discuss the implications for the publication of this rich dataset and how this may be used by the community.