Limitations in the process of transcription and translation inhibit recombinant human chorionic gonadotropin expression in CHO cells

• Human chorionic gonadotropin (hCG) is a heterodimer that consists of a α subunit noncovalently associated with a β subunit.
• The cell lines at the high and low-producing levels which were able to express hCG stability were screened by Flp-In™ system.
• We achieved more comprehensive understanding of the probable limitations throughout the gene expression pathway of the hCG.

Human chorionic gonadotropin (hCG) is a glycoprotein hormone that exists as a heterodimer with a α subunit and β subunit assembled together with disulfide bridges. This hormone plays an important role in the detection of ovulation induction and in the treatment of certain diseases that cause female infertility. The effects of transcription, subunit expression, assembling and secretion on recombinant hCG expression in CHO cells were studied using stable high-producing and low-producing cell lines generated by the FLP-In™ system. The results indicated that the mRNA and polypeptide levels of the β subunit were always higher than those of the α subunit. Further study confirmed that the differences were caused by the transcription rate rather than by mRNA stability. In the high-producing cell lines, there was obvious transcription level limitation of the α subunit in contrast to the β subunit. In addition, there was obvious limitation of the synthetic steps from mRNA to polypeptide for both the α subunit and the β subunit, especially the β subunit. Significant limitations of the assembly and secretion levels were not observed in this research. This study presents a research methodology for double subunit protein expression and provides valuable evidence for the enhancement of recombinant hCG productivity.