Differential expression of transcriptional corepressors NCoR and SMRT in leukemic cells and nonhematopoietic adherent cells. (A) Fifty micrograms of total RNA were analyzed by Northern blot. A 10-kb major transcript, SMRTα isoform, was detected in all cell lines examined. Note the presence of an 8.5-kb transcript, SMRTβ isoform, only in the nonhematopoietic adherent cells and its absence in all the hematopoietic cell lines tested. (B) Nuclear extracts of Jurkat, NB4, Cos-1, HeLa, and T47-D were subjected to Western blot analysis for SMRTα (top band) and SMRTβ (bottom band). Note the presence of a SMRTβ isoform only in the nonhematopoietic adherent cells and its absence in all the hematopoietic cell lines tested. (C) Overexpression of SMRTβ, but not SMRTα, induces ATRA binding to PML/RARα I410T in NB4-MRA1 cells. Nuclear extracts of cells transfected with SMRTβ (▾) or SMRTα (○) were incubated with 10 nM [³H]-ATRA and subjected to HPLC analysis using a 6 HR 10/30 size exclusion column. Nuclear extracts of NB4-MRA1 transfected cells with SMRTβ or SMRTα were subjected to Western blot analysis. The arrow indicates expression of the 110-kDa PML/RARα wild-type or mutant I410T.