Human papillomavirus type 16 (HPV-16) is the cause of cervical cancer. The HPV genome encodes three transforming proteins, E5, E6 and E7. E6 and E7 are the main transforming proteins of HPV, while the role of E5 is still poorly understood. Using three dimensional organotypic raft cultures we show that HaCaT human keratinocytes expressing HPV-16 E5 form a very perturbed epithelium, with simultaneous hyperkeratinization of some cells and defective differentiation of other cells. The basal layer is disturbed and many cells invade the collagen matrix. Many cells among the differentiated layers show characteristics of basal cells: progression through the cell cycle, expression of cytokeratin 14, lack of cytokeratin 1 and production of matrix metalloproteases (MMP). Using deletion mutants which encompass the three hydrophobic domains of E5, we have assigned the ability to promote invasion of the matrix to the first hydrophobic domain, and the capacity to induce MMP9 to the C-terminal four amino acids. We also show that invasion and production of MMP9 can be dissociated, as mutants that are still capable of invasion do not produce MMP9 and vice versa.
INTRODUCTIONHuman papillomaviruses (HPVs) infect mucosal and cutaneous epithelia and induce lesions that can persist and progress to cancer; this is particularly so for HPV-16, the major cause of cervical cancer. The HPV genome encodes three transforming proteins, E5, E6 and E7. E6 and E7 are the main transforming proteins of HPV, while the role of E5 is still poorly understood. While E6 and E7 are expressed throughout the course of the disease and are necessary for the maintenance of a transformed phenotype, E5 is expressed during the early stages of infection and its expression is often, but not always, extinguished as the lesion progresses towards malignancy (Cavuslu et al., 1996;Chang et al., 2001;Kell et al., 1994).E5 of HPV-16 is a hydrophobic membrane-associated protein 83 aa long, with three well-defined hydrophobic regions, believed to be transmembrane domains, and short regions at the N and C termini that may extend beyond the lipid bilayer. E5 is localized in the endomembranes of the infected cells, the Golgi apparatus and the endoplasmic reticulum (Suprynowicz et al., 2006). The functions of E5 appear to be multiple. E5 binds to the 16K subunit c (a component of the proton pump vacuolar ATPase) (Conrad et al., 1994) and reduces acidification of the endomembrane compartments (Schapiro et al., 2000;Straight et al., 1995), resulting in the sustained activation of the receptor for epidermal growth factor (EGF-R) (Straight et al., 1993). Likely through the activation of EGF-R, E5 is also responsible for the activation of other kinases, such as MAP kinase and PI3 kinase (Crusius et al., 1997;Kim et al., 2006). The impeded acidification of the Golgi apparatus and other organelles is likely to be 3These authors contributed equally to this work. , 2005, 2006). In transgenic mice, E5 alters the growth and differentiation of stratified epithelia and induces epithelial t...