CHOP negatively regulates the C/EBPϵ-dependent up-regulation of the myeloid-specific target promoter, lactoferrin. COS-1 and U937 cells were transfected with a lactoferrin promoter reporter construct (pLactoferrin-luc) in combination with different expression vectors, as indicated below the graph. The total amount of DNA was kept equal in each transfection with the addition of empty vector. All transfections included the pRL-TK vector, which served as an internal control for transfection efficiency. Results represent the mean ± SD of triplicate (COS-1 cells) or duplicate (U937 cells) transfections. ϵ, C/EBPϵ; α, C/EBPα.