Down-regulation of cold inducible RNA-binding protein using siRNA does not overcome hypothermic growth arrest

Abstract

When cells are cultured in low temperature (32°C), cold inducible RNA-binding protein (cirp) is highly expressed, which is known to suppress cell growth in low temperature. In low temperature, specific productivity (qp) of recombinant CHO (rCHO) cells producing foreign protein is increased and the quality of foreign protein is enhanced against normal temperature (37°C). But lowed specific growth rate of rCHO cells is an obstable to high production of therapeutic proteins. We cloned CHO cirp cDNA and vector based siRNAs against cirp down-regulate cirp stably both mRNA level and protein level. From the experiments of these cirp down-regulated clones, we could find specific growth rates of cirp down-regulated clones are not recovered in compared with control in low temperature culture. And, specific growth rate of the clones with highly expresed level of cirp was not reduced in compared with that of clones with normaly expressed level of cirp. Specific productivity of cells was relatively constant regardless of cirp expressioin levels, too. Cell cycle distributions of cells of which cirp is down-regulated in low temperature are similar to control, and cirp over-expressed clones showed the same results, too. So we concluded that in CHO cells, down-regulation of only cirp is not sufficient to recover growth arrest in low temperature culture.