Human papillomavirus type 16 E5 gene stimulates the transforming activity of the epidermal growth factor receptor

We have until recently made several unsuccessful attempts to assign any activity to the human papillomavirus type 16 (HPV-16) E5 gene product. However, studies with the bovine papilloma virus 1 (BPV-1) E5 protein indicated an interaction with the epidermal growth factor receptor (EGFR). In light of the overall similarity between the HPV and BPV E5 proteins we attempted to determine whether the HPV-16 E5 gene had any common activity. In cells expressing high levels of EGFR plus HPV-16 E5 we found a dramatically increased proliferative activity in soft-agar assays in the presence of EGF. The specificity of this activity was monitored by the addition of other mitogenic agents. The phorbol ester phorbol 12-myristate 13-acetate (PMA) had no effect on the E5-containing cells, although insulin weakly stimulated their growth in soft agar. Further analysis revealed the same number of EGF receptors were present on the E5-containing cells as on the control cells, although the E5 cells were more sensitive to lower concentrations of EGF. These results imply that E5 is amplifying the mitogenic signals from the EGFR in an as yet unknown manner, but which may form the basis of interactions with a variety of growth factor receptors. This report brings to three the number of transforming genes encoded by HPV-16.