Effect of RA on gene expression of U937PR9 (retinoid-sensitive) and U937B412 (retinoid-resistant) cells. Pair-wise comparisons were performed to examine the retinoid-treatment effect; data from retinoid untreated cells were compared with those from retinoid-treated cells (U937 vs RA-treated U937; U937PR9 vs RA-treated U937PR9; U937B412 vs RA-treated U937B412). Triplicate experiments were performed in a paired fashion at 3 different times. (A) Venn diagrams of genes that are up-regulated by RA in each of 3 independent experiments. The criteria for altered gene expression include 2-fold or more change in the raw values, and raw expression values of at least 1000 in the experimental group. (B) Northern blot analysis of RA-regulated genes. Northern blot analysis using the same samples of total RNA used in the microarray analysis confirmed the RA regulation of genes from microarray data. In addition, effect of protein synthesis inhibitor cycloheximide (CHX) on retinoid-dependent gene expression was examined. U937PR9 cells were incubated with CHX (10 μg/mL) alone, CHX and ATRA (10^-6 M), or ATRA alone for 0 and 6 hours. Each blot was rehybridized for GAPDH to ensure equal loading of RNA.