多药耐药基因的转录调控与治疗学机会

人肿瘤多药耐药mdr-1基因的转录调控机制复杂。多个正调控和负调控元件与转录因子的相互作用、表遗传学因素的参与等共同决定着人mdr-1基因表达的组织、细胞和刺激的特异性和依赖性。同时,也为特异或相对特异性地防止／抑制肿瘤细胞的mdr-1基因表达、克服肿瘤多药耐药性提供了基础。新抗肿瘤药物沙尔威辛和ET-743有力地诠释了控制mdr-1基因转录所蕴藏的治疗学机会。     

Three steroidogenic factor-1 binding elements are required for constitutive and cAMP-regulated expression of the human adrenocorticotropin receptor gene

In the present study, we characterized two new SF-1 binding sites, SF-209 and SF-98, in the promoter of the human ACTH receptor (hACTH-R) gene. Both sites, together with the previously described SF-35 site, are required for full constitutive activity of this gene. This was demonstrated by the use of constructs containing part of the promoter upstream of the luciferase gene and carrying mutation in one of these sites, to transiently transfect H295R cells. Mutations of either SF-35, SF-98, or SF-209 induced a decrease of luciferase activity. This effect was amplified when two or three elements were mutated together in the same construct. Only SF-35 and SF-98 seem to play a major role in the cAMP-induced regulation of the hACTH-R gene, since mutation of either one of these sites reduced the forskolin induction of luciferase activity by 50%. When both elements were mutated, no stimulation was obtained over the control. This indicates that SF-1 protein must bind to both sites for the cAMP response.     

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 G(2)/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 G(0) and G(1) but no significant change in G(2). Removal of upstream sequences including an E-box and Sp1 site eliminated the TSA induced increase in G(0) and G(1), and caused a decrease in promoter activity during S and G(2). Promoter activity increased only 2-fold following TSA treatment of G(0) cells containing the construct pCycB(MUT-E-Box)-LUC with an E-box mutation, and a decrease in activity was detected during G(2). We conclude that histone deacetylation contributes to the repression of cyclin B1 expression in G(0) and G(1), and that this mechanism requires, in part, the E-box. TSA reduction of cyclin B1 promoter activity in G(2), however, involves sequences within the first 119 bp. A working model for cyclin B1 regulation is provided.