FIG. 4.

PER1 and PER2 inhibit ERβ transactivation through CLOCK-BMAL1. (A and B) Cotransfection of PER1 (A) or PER2 (B) represses expression of the mERβ- and hERβ-regulated luciferase reporter gene constructs activated by CLOCK-BMAL1 in HeLa cells. + and ++ correspond to 250 and 500 ng of PER1 and PER2 expression plasmids, respectively. (C) CLOCK siRNA blocks the ability of PER1 to repress basal activity of pGL3 mERβ in HC11 cells. CLOCK expression levels in HC11 cells were assessed by Western blotting. Results were compared to basic luciferase activity of pGL3-ERβ alone, which was arbitrarily set to be 1, and expressed as means ± standard deviations of three independent experiments performed in triplicate.*, P < 0.05 (Student's t test).