Enhancement of expression of an introduced gene by 5-azacytidine in mammalian cell lines

We transfected a mouse myeloma cell line, P3/NS1-Ag4-1 (NS-1), and a Chinese hamster ovary cell line, CHO-K1 with the β-galactosidase (β-Gal) gene of Escherichia coli, and isolated stable transformants designated as NS-1Z/gpt and CHO-Z/neo, respectively. When NS-1Z/gpt cells were incubated with 5-20 μM 5-azacytidine (5-azaC), the specific and total activity of β-Gal were enhanced 2-to 3-fold and 1.5- to 2-fold, respectively. In CHO-Z/neo cells, similar treatment resulted in a 3- to 5-fold increase in the specific β-Gal activity and about a 2-fold enhancement in total enzyme activity. The growth of both cell lines was inhibited by more than 80% in the presence of 10 μM 5-azaC. It was confirmed in immunotitration experiments that the enhancement of β-Gal activities was due to an increase in the enzyme protein. Northern blot analysis revealed that 5-azaC-treatment resulted in the enhanced expression of β-Gal mRNA. 5-AzaC also enhanced the production of human interleukin 2 (IL2) from CHO cells that were transfected with the IL2 gene. On the other hand, 5-azaC did not significantly affect the expression of an endogenous gene like lactate dehydrogenase or β-actin. These results suggest that 5-azaC is a useful agent for up-regulating the expression of introduced genes.