Investigating novel host factors promoting human papillomavirus infection

Project Summary/Abstract: Human papillomavirus (HPV) infects nearly 80 million U.S. adults, and is the primary cause of cervical, anogenital, and oropharyngeal cancers. Unfortunately, HPV vaccines have been poorly utilized and provide no therapeutic value for existing infections, leaving much of the population susceptible to HPV-related cancers. To

initiate infection, HPV binds to a series of extracellular receptors and is endocytosed by the host cell. HPV is then recruited to the host factor γ-secretase in the endosome by an unknown mechanism, enabling it to act as a chaperone to insert the viral capsid protein L2 across the endosomal membrane. This exposes

L2 to the cytosol, which in turn recruits host factors that direct the virus along an infectious route through the Golgi apparatus and to the nucleus. Despite HPV’s significant impact on human health, there is limited understanding of its specific entry pathway through the host cell. Preliminary data suggest a role for the host p120-catenin (p120) in regulating the early trafficking steps of HPV

along an infectious route. Our research group first identified an HPV-p120 interaction via mass-spectrometry, and we have since demonstrated that this interaction occurs at early infection time-points. Importantly, p120 is essential for productive HPV infection. Further experiments suggest that p120 is required for targeting HPV to γ-

secretase for insertion of the viral capsid protein L2 across the endosomal membrane. However, as p120 is a cytosolic factor, it must be interacting with HPV via a transmembrane protein. Thus, we tested the role of cadherins – transmembrane cell adhesion molecules known to bind both p120 and γ-secretase – in HPV

infection. Preliminary data show that in addition to binding HPV at early time-points, cadherins are also required for productive HPV infection. Together, these data suggest the cell-adhesion cadherin molecule, in conjunction with cytosolic p120, binds to HPV at the cell surface, and promotes endocytosis of the virus

to the endosome. As p120 is known to deliver cadherin to γ-secretase, we further hypothesize that p120 targets the HPV-cadherin complex to endosome-localized γ-secretase so that the virus can reach γ- secretase for membrane insertion of the viral protein L2. To further test this hypothesis, we will elucidate the

precise mechanism by which the cadherin-p120 complex promotes endocytosis of HPV to the endosome to initiate HPV infection (Aim 1), and how p120 then targets the virus to γ-secretase for membrane insertion (Aim 2) – a critical step of infection. The combined use of cell-based, biochemical, and infection studies will be

employed to tackle the questions at hand. Insights gained through these studies should illuminate intrinsic intracellular transport mechanisms. More importantly, identifying the cellular factors mediating HPV infection may provide new therapeutic strategies to combat HPV infections.