TRANSCRIPTIONAL REGULATION OF THE MDR1 GENE BY HISTONE ACETYLTRANSFERASE AND DEACETYLASE IS MEDIATED BY NF-Y

Recent studies have shown that the histone-modifying enzymes histone a cetyltransferase (HAT) and histone deacetylase (HDAC) are involved in transcriptional activation and repression, respectively. However, litt le is known about the endogenous genes that are regulated by these enz ymes or how specificity is achieved. In the present report, we demonst rate that HAT and HDAC activities modulate transcription of the P-glyc oprotein-encoding gene, MDR1. Incubation of human colon carcinoma SW62 0 cells in 100-ng/ml trichostatin A (TSA), a specific HDAC inhibitor, increased the steady-state level of MDR1 mRNA 20-fold. Furthermore, TS A treatment of cells transfected with a wild-type MDR1 promoter/lucife rase construct resulted in a 10- to 15-fold induction of promoter acti vity. Deletion and point mutation analysis determined that an inverted CCAAT box was essential fdr this activation. Consistent with this obs ervation, overexpression of p300/CREB binding protein-associated facto r (P/CAF), a transcriptional coactivator with intrinsic HAT activity, activated the wild-type MDR1 promoter but not a promoter containing a mutation in the CCAAT box; deletion of the P/CAF HAT domain abolished activation. Gel shift and supershift analyses identified NF-Y as the C CAAT-box binding protein in these cells, and cotransfection of a domin ant negative NF-Y expression vector decreased the activation of the MD R1 promoter by TSA. Moreover, NF-YA and P/CAF were shown to interact i n vitro. This is the first report of a natural promoter that is modula ted. by HAT and HDAC activities in which the transcription factor medi ating this regulation has been identified.