Cytokines regulate endogenous RAR activity in cultured hematopoietic precursors.

The lin⁻ c-kit⁺ Sca-1⁺hematopoietic precursors were isolated from normal mouse bone marrow and cultured in liquid suspension as detailed in “Materials and methods.” After 21 days these cells were washed and then cultured for an additional 2 days in either SCF alone, SCF plus IL-3, or GM-CSF alone as indicated. These different cytokine-stimulated cells were then transfected with the RXR/RAR-responsive RARE tk-LUC reporter and cultured for an additional 5 hours in the presence or absence of the indicated concentration of ATRA. Relative luciferase activity was then determined on harvested cell extracts using a β-galactosidase reporter as an internal control.