E2F1 binds and activates the Trib2 promoter. (A) 293T, 3T3, and RAW264.7 cells were cotransfected with empty pGL3 Basic or 500-bp Trib2 promoter or 2.6-kb Trib2 promoter constructs and luciferase activity was measured. (B) Schematic presentation of the Trib2 promoter region 2.6 kb upstream from the transcriptional start site and the location of 3 putative E2F binding sites. (C) 3T3 cells were cotransfected with E2F1 or pcDNA empty expression vector and Trib2 luciferase reporter plasmids (pGL3 control, 500-bp, or 2.6-kb promoter region) and luciferase activity was measured. (D) 3T3 cells were cotransfected with E2F1 or E2F1 E132 DNA binding deficient mutant expression vectors and Trib2 luciferase reporter constructs (pGL3 control or 2.6-kb promoter) and luciferase activity was measured. Data presented are mean ± standard deviation (SD) of duplicate cultures and representative of 3 independent experiments. **P < .005 and ***P < .001 using an unpaired Student t test. (E) K562 cells were cotransfected with E2F1 or E2F1 E132 DNA binding deficient mutant expression vectors or empty control vector and Trib2 luciferase reporter constructs (pGL3 control or 2.6-kb promoter) and luciferase activity was measured. Data presented are mean ± SD and representative of 3 independent experiments. **P < .005 using an unpaired Student t test.