IL-3 enhances exogenous RAR activity in transfected EML cells.

(A) Mutating a 5–amino acid region within the DNA-binding domain (P-box) of RARα (EGCKG) to mimic the glucocorticoid receptor P-box (GSCKV) creates a mutated RAR (designated RARα-PGR) that now, together with its RXR partner, activates a novel DR-5 harboring a glucocorticoid response element (designated DR-5 R5G). In contrast, the wild-type RXR-RAR heterodimer neither binds to nor activates this novel DR5-R5G response element. (B) EML cells were transfected with expression vectors for both the normal RXRα and the engineered RARα-PGR together with the luciferase reporter harboring the corresponding DR-5 R5G response element. Cells were then cultured in the indicated concentration of ATRA for 5 hours and cell extract luciferase activity determined. Results are the mean of at least 3 independent experiments.