RT-PCR analysis of TM mRNA in NB4 cells modulated by synthetic retinoids. Total RNA was extracted from cultured NB4 (A) or U937 cells (B) after exposure to 0.01 μmol/L of ATRA (lane 2), Ch55 (lane 3), Am80 (lane 4), or Ro25-7386 (lane 7) and 1 μmol/L of Ro41-5253 (lane 6) for 5 hours. RT-PCR analysis of mRNA was performed as described in the Materials and Methods. Selective counteractive effect of Ro41-5253 (1 μmol/L) on the effect of ATRA was also observed (lane 5). Lane 1 represents untreated control. Basepair markers are given on the left.