Elucidating the role of requiem in the growth and death of Chinese hamster ovary cells.

Requiem, a hypothesized transcription factor with apoptosis-related activity, was previously shown to be a potential cell engineering gene target for improving recombinant protein production. Requiem suppression has resulted in improved viable cell density and extended culture viability, leading to an overall improvement in recombinant protein productivity. However, not much is known about the function of requiem. We found that requiem is highly conserved at both nucleotide and amino acid levels in Chinese hamster ovary (CHO) cells when compared to human and mouse sequences, suggesting that requiem's functional role is evolutionary well conserved. Upon inducing requiem over-expression, proliferation rates of CHO cells were significantly decreased with doubling times increased by 26%. Interestingly, the over-expression of requiem did not decrease cell viability and could not induce apoptosis. However, requiem sensitized the cells to increased caspase-9 activities under staurosporine-induced apoptosis, suggesting that it has a role to play in mitochondria-mediated apoptosis under staurosporine treatment. The nuclear localization of REQUIEM in CHO cells and its conserved plant homeodomain (PHD) zinc fingers seem to further support the hypothesis that requiem encodes for a potential transcription factor. Upon requiem over-expression, we found that the differentially expressed genes involved in transcriptional regulation and cell proliferation and growth were associated both upstream and downstream of p53.

Engineering mammalian cells in bioprocessing - current achievements and future perspectives.

Over the past 20 years, we have seen significant improvements in product titres from 50 mg/l to 5-10 g/l, a more than 100-fold increase. The main methods that have been employed to achieve this increase in product titre have been through the manipulation of culture media and process control strategies, such as the optimization of fed-batch processes. An alternative means to increase productivity has been through the engineering of host cells by altering cellular processes. Recombinant DNA technology has been used to over-express or suppress specific genes to endow particular phenotypes. Cellular processes that have been altered in host cells include metabolism, cell cycle, protein secretion and apoptosis. Cell engineering has also been employed to improve post-translational modifications such as glycosylation. In this article, an overview of the main cell engineering strategies previously employed and the impact of these strategies are presented. Many of these strategies focus on engineering cell lines with more efficient carbon metabolism towards reducing waste metabolites, achieving a biphasic production system by engineering cell cycle control, increasing protein secretion by targeting specific endoplasmic reticulum stress chaperones, delaying cell death by targeting anti-apoptosis genes, and engineering glycosylation by enhancing recombinant protein sialylation and antibody glycosylation. Future perspectives for host cell engineering, and possible areas of research, are also discussed in this review.

Simultaneous targeting of Requiem & Alg-2 in Chinese hamster ovary cells for improved recombinant protein production.

Apoptosis is known to be the main cause of cell death in the bioreactor environment, leading to the loss of recombinant protein productivity. In a previous study, transcriptional profiling was used to identify and target four early apoptosis-signaling genes: FADD, FAIM, Alg-2, and Requiem. The resulting cell lines had increased viable cell numbers and extended culture viability, which translated to increased protein productivity. Combinatorial targeting of two genes simultaneously has previously been shown to be more effective than targeting one gene alone. In this study, we sought to determine if targeting Requiem and Alg-2 was more effective than targeting Requiem alone. We found that targeting Requiem and Alg-2 did not result in extended culture viability, but resulted in an increase in maximum viable cell numbers and cumulative IVCD under fed-batch conditions. This in turn led to an approximately 1.5-fold increase in recombinant protein productivity.