The synergism between bovine papillomavirus type 4 and quercetin is dependent on the timing of exposure.

Exposure to the flavonoid quercetin and transfection with bovine papillomavirus type 4 (BPV-4) DNA lead to oncogenic transformation of primary bovine cells. Here we show that the synergism between quercetin and BPV-4 (or its E7 oncogene) is stronger the shorter the interval between the two treatments. Quercetin immortalizes transformed cells, confers anchorage-independent growth and induces tumorigenicity in cells transfected only with the E7 oncogene.