Controlling glycosylation of recombinant proteins produced by CHO cells is highly desired as it can be directed towards maintaining or increasing product quality. To further our understanding of the different factors influencing glycosylation, a glycosylation sub-array of 79 genes and a capillary electrophoresis method which simultaneously analyzes 12 nucleotides and 7 nucleotide sugars; were used to generate intracellular N-glycosylation profiles. Specifically, the effects of nucleotide sugar precursor feeding on intracellular glycosylation activities were analyzed in CHO cells producing recombinant human interferon-gamma (IFN-gamma). Galactose (+/-uridine), glucosamine (+/-uridine), and N-acetylmannosamine (ManNAc) (+/-cytidine) feeding resulted in 12%, 28%, and 32% increase in IFN-gamma sialylation as compared to the untreated control cultures. This could be directly attributed to increases in nucleotide sugar substrates, UDP-Hex ( approximately 20-fold), UDP-HexNAc (6- to 15-fold) and CMP-sialic acid (30- to 120-fold), respectively. Up-regulation of B4gal and St3gal could also have enhanced glycan addition onto the proteins, leading to more complete glycosylation (sialylation). Combined feeding of glucosamine + uridine and ManNAc + cytidine increased UDP-HexNAc and CMP-sialic acid by another two- to fourfold as compared to feeding sugar precursors alone. However, it did not lead to a synergistic increase in IFN-gamma sialylation. Other factors such as glycosyltransferase or glycan substrate levels could have become limiting. In addition, uridine feeding increased the levels of uridine- and cytidine-activated nucleotide sugars simultaneously, which could imply that uridine is one of the limiting substrates for nucleotide sugar synthesis in the study. Hence, the characterization of intracellular glycosylation activities has increased our understanding of how nucleotide sugar precursor feeding influence glycosylation of recombinant proteins produced in CHO cells. It has also led to the optimization of more effective strategies for manipulating glycan quality.

A combined transcriptome and proteome analysis was carried out to identify key genes and proteins differentially expressed in Chinese hamster ovary (CHO) cells producing high and low levels of dhfr-GFP fusion protein. Comparison of transcript levels was performed using a proprietary 15K CHO cDNA microarray chip, whereas proteomic analysis was performed using iTRAQ quantitative protein profiling technique. Microarray analysis revealed 77 differentially expressed genes, with 53 genes upregulated and 24 genes downregulated. Proteomic analysis gave 75 and 80 proteins for the midexponential and stationary phase, respectively. Although there was a general lack of correlation between mRNA levels and quantitated protein abundance, results from both datasets concurred on groups of proteins/genes based on functional categorization. A number of genes (20%) and proteins (45 and 23%) were involved in processes related to protein biosynthesis. We also identified three genes/proteins involved in chromatin modification. Enzymes responsible for opening up chromatin, Hmgn3 and Hmgb1, were upregulated whereas enzymes that condense chromatin, histone H1.2, were downregulated. Genes and proteins that promote cell growth (Igfbp4, Ptma, S100a6, and Lgals3) were downregulated, whereas those that deter cell growth (Ccng2, Gsg2, and S100a11) were upregulated. Other main groups of genes and proteins include carbohydrate metabolism, signal transduction, and transport. Our findings show that an integrated genomic and proteomics approach can be effectively utilized to monitor transcriptional and posttranscriptional events of mammalian cells in culture.

Based on the transcriptional profiling of CHO cell culture using microarray, four key early apoptosis signaling genes, Fadd, Faim, Alg-2, and Requiem, were identified and CHO GT (Gene Targeted) cell lines were developed by targeting these four genes. Two were CHO GT(O) cell lines overexpressing anti-apoptotic genes, Faim and Fadd DN and two were CHO GT(KD) cell lines involving knockdown of Alg-2 and Requiem which are pro-apoptotic genes using small interfering RNA (siRNA) technology. Comparisons of these CHO GT cell lines with the parental cell line in batch culture (BC) and fed-batch culture (FBC) were performed. Compared to parental cells, the CHO GT cell lines showed apoptosis resistance as they significantly delayed and/or suppressed initiator caspase-8 and -9 and executioner caspase-3 activities during culture. FBC of CHO GT cell lines reached significantly higher maximum viable cell densities (up to 9 x 10(6) cells/mL) compared with the parental cell line (5 x 10(6) cells/mL). The recombinant interferon gamma (IFN-gamma) yields were increased by up to 2.5-fold. Furthermore, it was observed that the IFN-gamma was more highly sialylated.