CHO Cells Related to Three of the Most Important Post-translational Modifications (PTMs)

Current studies have confirmed that transient expression of recombinant antibodies with high titers can be obtained in Chinese hamster ovary (CHO) host (Expicho-S) cell lines. CHO cell engineering has become of particular interest in recent years following the publication of the CHO cell genome and the availability of data relating to the proteome, transcriptome, and metabolome of CHO cells.

PTMs Process

Data relating to cellular post-translational modifications (PTMs) came to fruition in recent years. PTMs are important to many cellular processes and can further alter proteins by increasing the complexity of the proteins and their interactions. To date, CHO cell studies have involved the three most important PTMs: glycosylation, phosphorylation, and ubiquitination.

Protein Glycosylation

Research has shown that IgG antibody-dependent cellular cytotoxicity (ADCC) can be improved by adding additional glycosyltransferase enzymes to CHO cell lines. The glycosylation patterns of recombinant proteins are important and can be impacted by several basic culture parameters, including pH, oxygen levels within bioreactors, and ammonia levels. Glycosylation patterns of recombinant proteins can differ based on the cell line chosen due to the differences in the array of glycol-syltransferase enzymes between cell lines.

Fig. 1 Role of glycans in cellular function. Many mechanisms can alter the expression, activity, and structure of cellular glycosyltransferase or glycosidase.

Protein Phosphorylation

Protein phosphorylation is important for many cellular functions including metabolism, apoptosis, proliferation, and subcellular trafficking. Phosphorylated amino acids are able to bind molecules, enabling them to interact with other proteins. The role of phosphorylation in important cellular functions can take several different forms. Phosphorylation can act as a molecular switch by phosphorylating and dephosphorylating proteins.

Protein Ubiquitination

Understanding the role of ubiquitination in intracellular pathways in CHO cells, as well as understanding the role of other important post-translational modifications such as phosphorylation, should provide opportunities to optimize CHO cells for the production of therapeutic biopharmaceuticals.

Fig.2 Typical workflow for identifying ubiquitinated peptides using the K-ε-GG remnant motif.

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