Human interleukin 1β fused to the human growth hormone signal peptide is N-glycosylated and secreted by Chinese hamster ovary cells

A hybrid gene consisting of the sequences coding for the signal peptide of human growth hormone and the mature form of interleukin-1β (IL-1β) was chemically synthesized. This sequence was inserted into a eukaryotic expression vector and introduced into Chinese hamster ovary cells. The resulting stably transformed cell lines produced large amounts of recombinant IL-1β, which was secreted into the culture medium mainly as a 22-kDa form. Expression in the presence of tunicamycin, an inhibitor of N-glycosylation, led to the complete disappearance of the 22-kDa form and the appearance of a new form of 17.5 kDa, indicating that the hybrid protein had been both processed and N-glycosylated. However, transformed cells producing mature IL-1β without a signal peptide produced the predicted 17.5-kDa nonglycosylated form. These results suggest that fusion to a heterologous leader sequence allowed IL-1β to be translocated across the membrane of the endoplasmic reticulum and to be transported and secreted by the exocytotic pathway.