Human papillomaviruses (HPVs) are associated with the pathogenesis of a variety of human cancers, including
cervical and oropharyngeal cancers. The HPV E6 and E7 oncogenes are usually expressed to high levels in these cancers.
Previous studies have shown dysregulation of cellular microRNAs (miRNAs) in HPV-positive cell lines and cancer tissues
and recent studies have identified a few miRNAs whose levels are altered in the presence of the viral E6 and E7 proteins.
In order to identify all the cellular miRNAs whose expression may be affected by these oncoproteins, we carried out
microarray analysis using human foreskin keratinocytes (HFKs) expressing either or both of these two proteins. These
studies showed that 90 and 60 miRNAs were dysregulated in the presence of the E6 or the E7 protein, respectively. Of
these, 43 miRNAs were similarly affected in HFK-E6 and/or HFK-E7 when compared to control cells. The joint expression
of E6 and E7 proteins in HFKs caused changes in the levels of 64 miRNAs, of which 24 were similarly affected in
HFK-E6 and/or HFK-E7 cells relative to controls. The microarray experiments were validated by quantitative real-time
RT-PCR analysis of several differentially expressed miRNAs. Several miRNAs dysregulated by the E6 and/or E7 proteins
are known to be altered in a variety of human cancers. Furthermore, previously known cellular targets of these miRNAs
are involved in processes such as cell cycle regulation, apoptosis, cell-cell adhesion, cell mobility and proliferation, and
alterations in their levels may contribute to HPV-associated carcinogenesis. Taken together, the results of our studies suggest
that high risk HPV E6 and E7 proteins share the ability to regulate a subset of cellular miRNAs.