The endoplasmic reticulum and unfolded protein response in the control of mammalian recombinant protein production

Abstract

The endoplasmic reticulum (ER) of eukaryotic cells is involved in the synthesis and processing of proteins and lipids in the secretory pathway. These processing events that proteins undergo in the ER may present major limiting steps for recombinant protein production. Increased protein synthesis, accumulation of improperly processed or mis-folded protein can induce ER stress. To cope with ER stress, the ER has quality control mechanisms, such as the unfolded protein response (UPR) and ER-associated degradation to restore homeostasis. ER stress and UPR activation trigger multiple physiological cellular changes. Here we review cellular mechanisms that cope with ER stress and illustrate how this knowledge can be applied to increase the efficiency of recombinant protein expression.

Improving the secretory capacity of Chinese hamster ovary cells by ectopic expression of effector genes: Lessons learned and future directions

“…This multitude of studies showing positive effects clearly underpins the potential of modulating the expression of effector genes. However, as previously pointed out (Hussain et al, 2014;Kim et al, 2012;Mohan et al, 2008), some effector genes are flawed by inconsistent effects. To exemplify this, all published studies on rprotein productivity (volumetric productivity or q p ) in CHO cells with the ectopic expression of the widely studied protein disulphide isomerase (PDI) are listed in Table 1.…”

“…In contrast to PDI, the effect of many effector genes on volumetric productivity or q p has only been reported once (Hussain et al, 2014;Nishimiya, 2013). Notwithstanding product specificity, it is likely that a considerable number of these effects are conditional -for example, specific to the monoclonal cell line or the expression platform being used.…”

“…Differences in the translation rate have been predicted between stable monoclonal CHO cell lines expressing the same MAb by mathematical modelling (O'Callaghan et al, 2010), suggesting that the effect of YY1 could be an increased translation rate. Alternatively, it could be a decreased degradation of folding intermediates mediated by the ER-associated degradation pathway (Hussain et al, 2014;Merulla et al, 2013) or autophagy-and lysosomal-mediated degradation (Kim et al, 2013). Nevertheless, the YY1 example implies that a secretion bottleneck phenotype does not seem to be a prerequisite for improving q p .…”

“…In many cases, such engineering efforts have led to positive effects on q p on a variety of r-proteins (see recent reviews (Fischer et al, 2015;Hussain et al, 2014;Nishimiya, 2013)). This multitude of studies showing positive effects clearly underpins the potential of modulating the expression of effector genes.…”

A protein chimera strategy supports production of a model “difficult‐to‐express” recombinant target

“…Efficient recombinant protein production of secreted targets in mammalian cells requires the balance between different steps/processes as proteins process through the complex secretory pathway 3, 4, 5. Limitations in the secretion of recombinant proteins can impact both protein quality and yield, which can have a negative impact on downstream processes.…”