Engineering the endoplasmic reticula of recombinant chinese hamster ovary cells for enhanced protein production

Abstract

Chinese Hamster Ovary cells have been used as the host cell line for the expression of many of the therapeutic proteins currently produced in mammalian cells. Process development has focused on aspects such as optimization of expression vector, medium formulation and bioreactor conditions and has successfully generated marketable quantities of proteins. However, the demand for therapeutics is ever-growing which necessitates a continuous research in this field to enhance protein production from mammalian cells. This study primarily focuses on the protein factories of the cell, the Endoplasmic reticulum (ER). The ER is the first compartment in an ordered membranous network called the secretory pathway. This pathway is responsible for the synthesis, modification, and delivery of biologically active proteins to their proper target sites within the cell and the extracellular milieu. As with many other biochemical pathways, flux through the secretory pathway is controlled at its early steps. The ER is the entry site for the vast majority of proteins processed in the secretory pathway. Early steps in the maturation of secretory proteins take place in the ER, e.g., the folding of the nascent polypeptide chains and posttranslational modifications important for proper folding and function of the protein. Transit from the ER to the Golgi complex is the rate-limiting step in secretion for many glycoproteins. Hence cells have to be relieved of this post-translational bottleneck for a higher heterologous protein expression. Engineering of molecular chaperones is one such strategy. The effect of overexpressing Protein disulfide isomerase (PDI) on thrombopoietin (TPO) and antibody (Ab) is studied. It was found that the overexpression of PDI had no effect on the specific productivity of TPO producing cells whereas it had a moderately positive effect on the specific productivity of Ab-producing cell line. Effect of overexpressing a molecular chaperone, PDI and its helper pr...