Cell cycle specific changes in the human cyclin B1 gene regulatory region as revealed by response to trichostatin A

The human cyclin Bl gene is cell cycle regulated with maximal activity during G2/M. We examined the role of histone deacetylation in cyclin Bl regulation using the histone deacetylase inhibitor trichostatin A (TSA). TSA treatment (100 ng/ml) of NIH3T3 cells containing the luciferase reporter construct pCycB(-287)-LUC caused an increase in promoter activity in G0 and G1 but no significant change in G2. Removal of upstream sequences including an E-box and Sp1 site eliminated the TSA induced increase in G0 and G1, and caused a decrease in promoter activity during S and G2. Promoter activity increased only 2-fold following TSA treatment of G0 cells containing the construct pCycB(MUT-E-Box)-LUC with an E-box mutation, and a decrease in activity was detected during G2. We conclude that histone deacetylation contributes to the repression of cyclin B1 expression in G0 and G1, and that this mechanism requires, in part, the E-box. TSA reduction of cyclin B1 promoter activity in G2, however, involves sequences within the first 119 bp. A working model for cyclin B1 regulation is provided.