Suppression of MicroRNA 424 Levels by Human Papillomaviruses Is Necessary for Differentiation-Dependent Genome Amplification.

High-risk human papillomaviruses (HPVs) link their life cycle to epithelial differentiation and require activation of DNA damage pathways for efficient replication. HPVs modulate the expression of cellular transcription factors, as well as cellular microRNAs (miRNAs) to control these activities. One miRNA that has been reported to be repressed in HPV-positive cancers of the cervix and oropharynx is miR-424. Our studies show that miR-424 levels are suppressed in cell lines that stably maintain HPV 31 or 16 episomes, as well as cervical cancer lines that contain integrated genomes such as SiHa. Introduction of expression vectors for miR-424 reduced both the levels of HPV genomes in undifferentiated cells and amplification upon differentiation. Our studies show that the levels of two putative targets of miR-424 that function in DNA damage repair, CHK1 and Wee1, are suppressed in HPV-positive cells, providing an explanation for why this microRNA is targeted in HPV-positive cells. We describe here for the first time a critical role for miR-424 in the regulation of HPV replication. HPV E6 and E7 proteins suppress the levels of miR-424, and this is important for controlling the levels of CHK1, which plays a central role in viral replication.