Dose-dependent induction of CD38 by ATRA and 4-oxo RA and its downmodulation by RAR-α antagonist. (A) RAR-α–transduced cells were incubated in the presence of increasing doses of ATRA or 4-oxo RA. (B) Cells were incubated overnight with 1 nmol/L ATRA or 4-oxo RA alone or simultaneously with increasing concentrations of RAR-α antagonist (Ro41-5253). At the end of the incubation period, cells were washed and analyzed for CD38 expression by flow cytometry, as described in the Materials and Methods. Data points represent the means of 2 experiments, with a standard deviation < 10% from the mean.