RA regulation of CHOP does not require new protein synthesis. The effect of a protein synthesis inhibitor, cycloheximide (CHX), on retinoid-dependent CHOP mRNA expression. NB4 cells were incubated with CHX (10 μg/mL) alone, CHX and ATRA (5 × 10^-7 M), or ATRA alone for 0, 1, and 4 hours. Northern blot analysis was carried out using total RNA (30 μg/lane) and hybridized with ³²P-labeled full-length CHOP cDNA probe. The same blot was rehybridized for GAPDH to ensure equal RNA loading.