p53/GFP are tightly regulated by Dox and it does not alter HPV18E6, a viral cell cycle deregulator. (A) Selected clones (HTet23p53, HTet26p53 and HTet43GFP from Additional file 2) were treated with 100 and 1000 ng/ml of Dox and after 48 h cell lysates were processed by western blotting for p53. β-Actin was used as a loading control. (B) Cells were treated as mentioned in (A) and processed for western blotting to detect GFP. β-Actin was used as a loading control. (C) HPV18 E6 mRNA levels were determined by semi-quantitative PCR. Cells treated with Dox were processed for RT-PCR. β-actin was used as a loading control. HTet43GFP and HeLa cells served as experimental controls.