(A) Schematic representation of ERα domains. (B–E) The ERα HBD functionally collaborates with CREB1. Luciferase reporter assays in HEK293T cells with fusion proteins of the DNA-binding domain of Gal4 with the indicated ERα domains: in panels B–E, the A/B domain containing the activation function AF1, the DNA-binding domain (domain C), the hinge (domain D), and the HBD with activation function AF2 (domains E/F). These were transiently coexpressed with wild-type CREB1, CREB1-S133A, and the dominant-negative CREB1 mutant (A-CREB1). (F) Luciferase reporter assay for Gal4-CREB1 activity in HEK293T cells. All values marked with an asterisk are statistically significantly different from their respective vector controls with P-values < 0.05.