Overexpressing the cytoplasmic poly(A)-binding protein gene Pabpc1 increases protein titers in Chinese hamster ovary (CHO) cell lines by 30–50%, according to researchers from BeOne Medicines (formerly BeiGene). Those results, published in a recent paper, appear consistent across multispecific and monoclonal antibodies.
For biomanufacturers, this suggests the possibility of a practical screening strategy to identify factors that could enhance expression levels or improve specific product attributes for certain genes expressed in CHO cells. Applicability to HEK293 or PER.C6 cells has not been studied.
Pabpc is considered crucial in mRNA stability and translation, and Pabpc1, specifically, extends the half-life of target mRNAs and orchestrates mRNA stability and pre-mRNA splicing. “Up to now, no studies have investigated the impact of Pabpc1 gene overexpression on recombinant protein production in CHO cells,” note Zhangying Jia, research scientist; Zheng Zhang, PhD, head of cell line development; Jing Song, PhD, vice president of biologics technical development; and colleagues at BeOne Medicines. This research offers insights regarding Pabpc1 that may enhance CHO cell expression in a production setting.
Jia and colleagues overexpressed Pabpc1 in a variety of low-expression clones used to produce monoclonal, bispecific, and trispecific antibodies. Growth rates were essentially identical to those of cells transfected with an empty vector, which served as the control. Of the three types of antibodies produced, expression level gains were greatest among bispecific antibodies, showing a 50% productivity increase. Trispecific antibodies showed a 32% productivity increase, and mAbs showed a 30% productivity increase. Other quality attributes were virtually identical between the overexpressed and control groups.
Additionally, “We discovered that Pabpc1 overexpression can modulate cellular metabolism to some extent,” according to the team. Consequently, lactic acid and ammonia accumulation were each lower in the overexpression groups than in the control groups. “These findings suggest that Pabpc1 overexpression may have a positive effect on regulating cellular metabolism by reducing the accumulation of toxic by-products… thereby creating a more favorable environment for protein production,” the scientists posit.
The team also reports an interaction between Pabpc1and the eukaryotic initiation factor 4E (eIF4E) that catalyzes subsequent reactions, leading to enhanced efficiency of translation initiation.
The enhanced productivity for both individual cells and overall titer that resulted from overexpressing Pabpc1 “is highly contingent upon the congruence between [a gene’s] functions and the intrinsic productivity bottlenecks of host cells,” they observed, noting that none of the other five genes that were overexpressed during this study (Slc25a32, Il19, Ptdss1, Stk3, and Mtdh) showed comparable results.
Exactly how overexpression of Pabpc1 enhances productivity of recombinant proteins in CHO cells “remains to be fully elucidated,” the scientists point out, but this strategy appears to be both novel and efficacious and offers “substantial potential for industrial application.”
The team plans to continue refining this strategy and broadening its applicability for biopharmaceutical manufacturing.
