Estrogen significantly represses HPV16 and HPV18 LCR transcription. (A and B) C33a cells were transfected with 1 μg of pgl3 basic backbone (control), 1 μg 16LCR-pGL3 (A) or in 1 μg 18-LCR-pGL3 (B) and grown in the presence or absence of 15 μM estrogen. (C) N/Tert-1 cells were transfected with 1 μg of pgl3 basic backbone or 1 μg 16LCR-pGL3 and grown in the presence or absence of 15 μM estrogen. Forty-eight hours after transfection, a luciferase-based assay was utilized to monitor levels of LCR transcription. Data are presented as relative fluorescence units (RFU), normalized to total protein concentration as monitored by a standard bovine serum albumin (BSA) assay. **, P < 0.001; ***, P < 0.0001.