Detailed understanding of enhanced specific productivity in Chinese hamster ovary cells at low culture temperature

The specific productivity of tumor necrosis factor receptor-immunoglobulin G1 Fc fusion (TNFR-Fc) (qTNFR-Fc) in Chinese hamster ovary (CHO) cells at 30°C was approximately 5-fold higher than that at 37°C. To investigate reasons for increased qTNFR-Fc at low culture temperature, TNFR-Fc mRNA levels were determined by real-time PCR. It was found that like qTNFR-Fc, the relative TNFR-Fc mRNA level was increased by lowering culture temperature, and more importantly, the kinetics of the increase in TNFR-Fc mRNA levels were in accordance with the changes in qTNFR-Fc. The results demonstrated that the increased transcriptional level of TNFR-Fc was responsible for the increased qTNFR-Fc at low culture temperature. Enhanced levels of mRNA could derive from increased gene copy number, improved mRNA stability, or enhanced transcriptional rate. There was not a big change of gene copy number by lowering culture temperature. The transcriptional rate of TNFR-Fc was slightly decreased at 30°C, compared to 37°C. However, mRNA stability of TNFR-Fc was significantly improved by lowering culture temperature. The half-life of TNFR-Fc mRNA was 5.55 h at 30°C, whereas that was 3.69 h at 37°C. Taken together, the reasons for the increased qTNFR-Fc in CHO cells at low culture temperature were mainly the enhanced TNFR-Fc mRNA levels, which resulted from the improved mRNA stability, rather than the changes in the gene copy number or the transcriptional rate.