Abstract
Oncogenic human papillomaviruses (HPVs) attach predominantly to extracellular matrix (ECM) components during infection of cultured keratinocytes and in the rodent vaginal challenge model in vivo. However, the mechanism of virion transfer from the ECM to receptors that mediate entry into host cells has not been determined. In this work we strove to assess the role of heparan sulfate (HS) chains in HPV16 binding to the ECM and determine how HPV16 release from the ECM is regulated. We also assessed the extent to which capsids released from the ECM are infectious. We show that a large fraction of HPV16 particles binds to the ECM via HS chains, and that syndecan-1 (snd-1) molecules present in the ECM are involved in virus binding. Inhibiting the normal processing of snd-1 and HS molecules via matrix metalloproteinases and heparanase dramatically reduces virus release from the ECM, cellular uptake and infection. Conversely, exogenous heparinase activates each of these processes. We confirm that HPV16 released from the ECM is infectious in keratinocytes. Use of a specific inhibitor shows furin is not involved in HPV16 release from ECM attachment factors and corroborates other studies showing only the intracellular activity of furin is responsible for modulating HPV infectivity. These data suggest that our recently proposed model, describing the action of HS proteoglycan processing enzymes in releasing HPV16 from the cell surface in complex with the attachment factor snd-1, is also relevant to the release of HPV16 particles from the ECM to promote efficient infection of keratinocytes.