Fig 10. HPV oncogenes control p21 expression at multiple levels.

E6 can repress p21 transcription at the promoter level by inducing the degradation of the p21 transcriptional activator p53; sustained E6/E7 expression maintains the concentration of miR-17 family members in HPV-positive cancer cells which repress p21 expression by targeting the p21 mRNA; the E7 protein can directly bind to the p21 protein and inhibit its function.