Transient transfection of wild-type and mutant LF89 plasmids in U937-C/EBP cells.

The C/EBPα gene under the control of a zinc-inducible metallothionein promoter was stably transfected into U937 cells. These cells can be made to undergo maturation along the granulocytic lineage after zinc induction, which results in high levels of C/EBPα expression. U937-C/EBPα cells were transiently transfected with LF89, a C/EBP mutant of LF89 (mLFC/EBP), or an SP1 (A) mutant of LF89 (mLFSP-1A) plasmids. One-half of the cells were induced with zinc for 48 hours after transfection (Zn induced), whereas the other one-half were incubated in medium without zinc (Uninduced); 2 μg of pCMVβgal plasmid was included in each transfection. Normalized luciferase values are represented as a ratio of luciferase activity with zinc to luciferase activity without zinc. The mean ± SE value for 3 experiments performed in duplicate are illustrated.