Mechanism of α-defensin HD5 Inhibition of Human Papillomavirus-16

Thesis (Ph.D.)--University of Washington, 2016-06

Human papillomavirus (HPV) is a significant oncogenic virus, but the innate immune response to HPV is poorly understood. Human α-defensin 5 (HD5) is an innate immune effector peptide secreted by epithelial cells in the genitourinary tract. HD5 is broadly antimicrobial, exhibiting potent antiviral activity against HPV at physiologic concentrations; however, the specific mechanism of HD5-mediated inhibition against HPV is unknown. During infection, the HPV capsid undergoes several critical cell-mediated viral protein processing steps, including unfolding and cleavage of the minor capsid protein L2 by furin. Using HPV16 pseudovirus, I show that HD5 interacts directly with the virus and inhibits the furin-mediated cleavage of L2. My data supports a model in which HD5 prevents furin from accessing L2 by occluding the furin cleavage site via direct binding to the viral capsid. This direct binding also results in capsid stabilization and inhibits viral uncoating inside the cell. The stabilized capsid cannot release L2, which is critical for endosomal exit of the viral genome. The HD5-HPV16 complex then traffics to the lysosome where the virus is degraded. These findings are similar to the model of HD5-mediated inhibition of other non-enveloped viruses, suggesting there is a general α-defensin antiviral mechanism of direct virus binding and capsid stabilization against non-enveloped viruses. In addition to elucidating the antiviral mechanism against HPV16, I have determined the physical properties of HD5 critical for neutralization of HPV16. These include the importance of both charge and paired arginine residues on one side of the HD5 molecule, as well as the disulfide stabilized structure and ability to dimerize. Overall, residues on one face of the HD5 molecule are necessary for antiviral activity against HPV16. Similar residues are also important for HD5 neutralization of human adenovirus, another non-enveloped virus. These studies may lead to a greater understanding of the interactions between α-defensins and non-enveloped viruses.