Human papillomavirus type 8 E7 protein binds nuclear myosin 1c and downregulates the expression of pre-rRNA.

Our aim was to search for new cellular binding partners for the E6 and E7 oncogenes of beta human papillomaviruses (HPV), whose direct role in skin carcinogenesis has not been thoroughly investigated. By employing glutathione S-transferase pulldown and coimmunoprecipitation, we identified nuclear myosin 1c as a binding partner of HPV 8 E7 protein. As nuclear myosin 1c is an essential component of the RNA polymerase I transcription complex, we studied the effects of HPV 8 E7 protein expression on ribosomal RNA (rRNA) expression. Here we show that the activity of RNA polymerase I is decreased and that pre-rRNA expression is consequently reduced due to HPV 8 E7 expression. However, the expression levels of mature cytoplasmic 18S and 28S rRNA are retained. We propose that by relieving their resources from the energy-consuming process of rRNA transcription, HPV 8 E7 expressing cells might support more efficient virus replication in the differentiating epithelium.