HDAC inhibitors sodium butyrate and sodium valproate do not affect human ncor1 and ncor2 gene expression in HL-60 cells

AIM. This study was designed to examine whether the class I and class IIa histone deacetylase (HDAC) inhibitors, sodium butyrate and sodium valproate alter the expression of human NCOR1 and/or NCOR2 genes coding for N-CoR (nuclear receptor corepressor) and SMRT (silencing mediator for retinoid and thyroid hormone receptors), respectively. METHODS: Human leukemia HL-60 cells were treated for 24 h with 0.5 and 1 mM sodium butyrate, 1 to 3 mM sodium valproate, 1 mcM all-trans retinoic acid (ATRA) or cotreated with 1 mcM ATRA and 0.5 mM sodium butyrate. The acetylation of histones H3 and H4 was analysed by western blotting. The levels of NCOR1 and NCOR2 mRNA were determined by quantitative real-time PCR. Expression of NCF2 gene coding for the NADPH oxidase subunit p67phox was evaluated as a marker of myeloid differentiation. Results. Both butyrate and valproate increased the acetylation of histone H3 at Lys9 and/or Lys14 as well as histone H4 at Lys12. Both HDAC inhibitors caused a significant increase in NCF2 mRNA levels without affecting NCOR1 or NCOR2 mRNA levels. Similarly, ATRA alone or in combination with butyrate induced NCF2 gene expression without any significant influence on the expression of NCOR1 or NCOR2 genes. CONCLUSION: We conclude that inhibitors of class I and class IIa HDACs do not alter the expression of human NCOR1 or NCOR2 genes and that the onset of myeloid differentiation is not accompanied by induction or repression of these genes in HL-60 cells.     

An LXXLL motif in nuclear receptor corepressor mediates ligand-induced repression of the thyroid stimulating hormone-beta gene

Nuclear receptor corepressor (N-CoR) regulates gene expression through interaction with DNA-bound nuclear receptors, recruiting multicomponent repressor complexes to the sites of target genes. We recently reported the presence of an LXXLL motif in N-CoR, and showed that this motif interacts in vitro and in vivo with retinoic acid receptor alpha (RARalpha) and thyroid hormone receptor beta (TRbeta). Transient transfection experiments now suggest that TRbeta and N-CoR act synergistically and may both be required for ligand-induced repression from the negative TR response element in the thyroid stimulating hormone-beta (TSHbeta) gene promoter. Mutation of the LXXLL motif in N-CoR abolished ligand-induced repression at this response element. Furthermore, in vitro binding of N-CoR to a complex between TRbeta and the negative TR response element was strictly ligand-dependent. We conclude that N-CoR and TRbeta cooperate in the regulation of the TSHbeta gene and that the ligand-dependent repression is mediated by the LXXLL motif in N-CoR.