2011 Publication

Abstract:

NF-YB, a subunit of the transcription factor, nuclear factor Y (NF-Y) complex, binds and activates CCAAT-containing promoters. Our previous work suggested that NF-YB may be a mediator of Top?, working through the Top2? promoter. DNA topoisomerase II (Top2) is an essential nuclear enzyme and the primary target for several clinically important anticancer drugs. Our teniposide-resistant human lymphoblastic leukemia CEM cells (CEM/VM-1-5) express reduced Top2? protein compared to parental CEM cells. To study the regulation of Top2? during the development of drug resistance, we found that NF-YB protein expression is increased in CEM/VM-1-5 cells compared to parental CEM cells. This further suggests that increased NF-YB may be a negative regulator of Top2? in CEM/VM-1-5 cells. We asked what causes the upregulation of NF-YB in CEM/VM-1-5 cells. We found by microRNA profiling that hsa-miR-485-3p is lower in CEM/VM-1-5 cells compared to CEM cells. MicroRNA target prediction programs revealed that the 3'-untranslated region (3'-UTR) of NF-YB harbors a putative hsa-miR-485-3p binding site. We thus hypothesized that hsa-miR-485-3p mediates drug responsiveness by decreasing NF-YB expression, which in turn negatively regulates Top2? expression. To test this, we overexpressed miR-485-3p in CEM/VM-1-5 cells and found that this led to reduced expression of NF-YB, a corresponding upregulation of Top2? and increased sensitivity to the Top2 inhibitor, etoposide. Results in CEM cells were replicated in drug-sensitive and -resistant human rhabdomyosarcoma Rh30 cells, suggesting that our findings represent a general phenomenon. Ours is the first study to show that miR-485-3p mediates Top2? downregulation in part by altered regulation of NF-YB.