The specific productivity of tumor necrosis factor receptor-immunoglobulin G1 Fc fusion (TNFR-Fc) (q(TNFR-Fc)) in Chinese hamster ovary (CHO) cells at 30 degrees C was approximately 5-fold higher than that at 37 degrees C. To investigate reasons for increased (q(TNFR-Fc)) at low culture temperature, TNFR-Fc mRNA levels were determined by real-time PCR. It was found that like q(TNFR-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 q(TNFR-Fc). The results demonstrated that the increased transcriptional level of TNFR-Fc was responsible for the increased q(TNFR-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 degrees C, compared to 37 degrees 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 degrees C, whereas that was 3.69 h at 37 degrees C. Taken together, the reasons for the increased q(TNFR-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. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.