Prior studies, which have relied upon the use of pseudovirions generated in heterologous cell types, have led to sometimes conflicting conclusions regarding the role of the minor capsid protein of papillomaviruses, L2, in the viral life cycle. In this study we carry out analyses with true virus particles assembled in the natural host cell to assess L2's role in the viral infectious life cycle. For these studies we used the organotypic (raft) culture system to recapitulate the full viral life cycle of the high-risk human papillomavirus HPV31, which was either wild type or mutant for L2. After transfection, the L2 mutant HPV31 genome was able to establish itself as a nuclear plasmid in proliferating populations of poorly differentiated (basal-like) human keratinocytes and to amplify its genome to high copy number, support late viral gene expression, and cause formation of virus particles in human keratinocytes that had been induced to undergo terminal differentiation. These results indicate that aspects of both the nonproductive and productive phases of the viral life cycle occur normally in the absence of functional L2. However, upon the analysis of the virus particles generated, we found an approximate 10-fold reduction in the amount of viral DNA encapsidated into L2-deficient virions. Furthermore, there was an over-100-fold reduction in the infectivity of L2-deficient virus. Because the latter deficiency cannot be accounted for solely by the 10-fold decrease in encapsidation, we conclude that L2 contributes to at least two steps in the production of infectious virus.Papillomaviruses are small icosahedral viruses with doublestranded, circular DNA genomes that infect the stratified squamous epithelial tissues of vertebrates. The infection commonly results in a papilloma, or wart, formation. A small subset of the human-specific genotypes termed the high-risk human papillomaviruses (HPVs), including HPV31, have the capacity to cause cancer, most notably cervical cancer (35). Understanding the papillomaviral life cycle may allow us to establish the means to inhibit high-risk papillomaviral infections and thereby prevent HPV-associated cancers. In this study, we investigated the role the minor capsid protein, L2, plays in the papillomaviral life cycle.The life cycle of papillomaviruses is intricately tied to the differentiation of their host tissue, stratified squamous epithelium (23). In the poorly differentiated basal cells, which comprise the proliferating compartment of the epithelium and where papillomaviral infection is thought to arise, the viral genome takes up residence as a stable, nuclear plasmid that is maintained at low copy number. Only a subset of viral genes, the early genes, is selectively expressed in the basal compartment, and therefore no new virus is made there. Consequently, we refer to the infective state in the basal compartment as the nonproductive phase of the life cycle. As basal cells proliferate and undergo cell division, daughter cells that lose contact with the underlying basement membr...

The papillomavirus life cycle is tied to the differentiation of the stratified squamous epithelium that this virus infects. The ability to study the papillomavirus life cycle is facilitated by organotypic culturing techniques that allow one to closely recapitulate this terminal differentiation process in the laboratory. Current techniques allow for the establishment of recombinant wild-type or mutant human papillomavirus (HPV) genomes in transfected early-passage human foreskin keratinocytes (HFKs). These cells can then be used in organotypic culture to investigate the role of individual viral genes in different aspects of the viral life cycle. When using early-passage HFKs, there is a need for the transfected HPV genome to extend the life span of the cells in order to have sufficient cell generations in which to carry out organotypic culturing. The recent isolation of a spontaneously immortalized HFK cell line that supports the complete HPV life cycle has further allowed investigators to study wild-type or mutant papillomaviral genomes that do not confer immortalization. In this chapter, we describe the methodologies that permit the study of the HPV life cycle in this HFK cell line.