Iron is the key factor in promoting PlGF expression. Iron-containing mesoporphyrin, but not mesoporphyrin alone, stimulates PlGF expression in K562 cells. K562 were grown and treated as in Figure 1. (A-B) HO-1 expression and PlGF expression. (C-D) Quantitative PCR results of HO-1 and PlGF expression from K562 cells treated with 20 µM zinc protoporphyrin (ZnPP) or 20 µM hemin or both. Cells were incubated with ZnPP for 30 minutes before hemin was included. (E) Differentially expressed transcripts in the microarray assay. (F) Quantitative PCR of EKLF from K562 cells treated as indicated.