Activation of the HOXB4 promoter by transient transfection with NF-Y, in cooperation with USF1/2. (A) NF-Y activates the HOXB4 promoter. K562 cells were transfected with 3 μg HOXB4 core promoter-coupled luciferase reporter plasmid and varying quantities (equimolar mixtures) of NF-Ya/b/c-expressing plasmids, with or without USF1- or USF2-expressing plasmids. Luciferase activities were measured 48 hours after transfection and normalized by Renilla reporter activities. The data presented are means ± SDs of triplicate measurements from 1 of 4 similar experiments. (B) HOXB4 promoter activity in the presence of DN-NF-Y. K562 cells were cotransfected with 10 μg HOXB4 promoter reporter plasmid along with varying doses of NF-YA29-expressing plasmid. (C) Endogenous HOXB4 expression in K562 cells is down-regulated by overexpression of DN-NF-Ya. The mRNA levels in transduced K562 cells were measured by real-time PCR in triplicate, as described in “Materials and methods.” The number of HOXB4 mRNA copies in the empty vector group was arbitrarily determined as 1. The data presented are means ± SDs (B-C).