Retinoid induction of HOTAIRM1 transcription. (A) Induction of HOTAIRM1 transcripts in NB4 cells incubated for up to 96 hours with ATRA (1 μM) or 9-cis-RA (1 μM), as indicated above each graph. Induction of HOTAIRM1 by ATRA was also measured in the presence of cycloheximide (100 μg/mL) in the culture media, as indicated. (B) Induction of the ATRA-resistant subline NB4r2, under the same conditions. (C) Comparison of CEBPE, HOXA1, and HOTAIRM1 induction in NB4 cells during 12-hour incubation with ATRA (1 μM). Relative expression levels of targets were measured by quantitative real-time RT-PCR, with results shown as ratios to the levels of uninduced reference cells. Bars and error lines represent means and SDs of results, normalized to an endogenous reference gene (TUBA1B or RPS6), of at least triplicate experiments for each group.