Early Interactions Between Human Papillomavirus Particles and the Host Cell

Open Access
Author:
Broutian, Tatevik Rafik
Graduate Program:
Microbiology and Immunology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 30, 2008
Committee Members:
  • Neil David Christensen, Thesis Advisor
Keywords:
  • binding
  • human papillomavirus
  • receptors
  • entry
Abstract:
Human papillomavirus (HPV) is a non-enveloped, double stranded DNA virus that infects the epithelial cells of the skin and mucosal membranes. A subset of HPVs infect the anogenital tract and are thus agents of sexually transmitted disease (STD). Within this subset are “low risk” types including HPV-6, -11 and -40 that primarily cause warts and “high risk” types including HPV-16, -18, and -31 which have been shown to induce cell transformations that develop into cancer. The World Health Organization (WHO) reports that more than 98% of all cervical cancers contain HPV DNA, and cervical cancer is the second leading cause of cancer-related deaths in women worldwide. Upon HPV infection, the virus gains access to the basal layer epithelium through a breach in the mucosal membrane. Following infection of the basal cells, the virus exploits the natural differentiation process of keratinocytes in order to replicate and produce progeny. The mechanism by which HPV infects basal cells at the site of wounding is currently unknown. Various in vitro models indicate that successful infection is the result of HPV binding to heparan sulfate moieties on surface proteins found on basal keratinocytes. Additional research indicates that á6-integrin may act as a secondary receptor for virus entry. In conjunction with these studies, previous research has established a direct binding interaction between HPV-11 virions and the extracellular matrix (ECM) component laminin 5. This ECM component was shown to serve as a transient receptor for HPV-11 entry into cells in culture. As a result of these studies, an alternate model of natural infection is proposed in which virions first bind to laminin 5 and then utilize this binding interaction to target basal keratinocytes migrating to the site of wounding. These various binding studies indicate that multiple virus attachment and entry mechanisms may be utilized by papillomaviruses. The general objective of this thesis is to gain insight into specific binding interactions that occur between different HPV types and the host cell or ECM during the attachment phase of the virus life-cycle. This main objective was pursued using virus-like particle (VLP) technology in conjunction with monolayer cells and various blocking reagents. Immunofluorescence studies looking at the binding pattern of various HPV types on fixed HaCaT cells and ECM revealed that different HPV types bind to the cell and ECM associated receptors with different affinities. HPV-6, -11 and -40 VLPs bind preferentially to the ECM component laminin 5, whereas HPV-16, -31, and -58 bind strongly to both the apical cell surface receptor and ECM component(s). Antibody and heparin blocking studies revealed that HPV utilizes different types of receptors for attachment to cells and ECM. Some virus types preferentially bind to a single receptor molecule whereas other virus types have evolved dual binding capabilities in order to ensure attachment. By determining the critical steps involved in HPV entry, we will gain a better understanding of the various virus-host cell interactions utilized for successful infection and this research can further translate into designing better drug targets for treatment.