Because E6 causes ubiquitin-mediated degradation of p53 [9] and because LPV had previously been shown to increase levels of p53 in E6-expressing cancer cells [34], we also monitored p53 protein levels in this experiment, observing moderate increases to p53 for the four protease inhibitors that decreased levels of E6 and E7 (Figure 2c). This evidence concerns the gene TP53 and cancer.