1,25(OH)₂D₃ and ATRA responsiveness of the TM RARE in OCI-AML3 cells and ECV304. OCI-AML3 and ECV304 cells were transfected with pTM-2RAREtkLUC containing two copies of the RARE from the TM gene, thymidine kinase promotor and LUC gene, and internal control plasmids. After 48 hours, ATRA (•) or 1,25(OH)₂D₃ (▪) were added and the cells were incubated for an additional 24 hours. Cells were procured, and cell extracts were assayed for LUC activity. Experiments were repeated independently four times. Values are means ± SD. *Significantly different from untreated controls (P < .05).