Regulation of splicing-associated SR proteins by HPV-16

HPV-16 (human papillomavirus type 16) is a small dsDNA (double-stranded DNA) virus which infects mucosal epithelial tissue of the cervix. Epithelial tissue is composed of a basal layer of cells, capable of division, and a number of suprabasal layers, wherein the cells become more differentiated the closer to the surface of the epithelium they become. Expression of viral proteins is dependent upon epithelial differentiation status, and, within the HPV-16 genome, several elements have been found which control expression both transcriptionally and post-transcriptionally. Expression of the highly immunogenic capsid proteins, L1 and L2, is restricted to only the most differentiated cells, where immune surveillance is limited. However, L1 and L2 transcripts can be detected in less differentiated cells, suggesting post-transcriptional mechanisms exist to prevent their expression in these cells. Indeed, a number of cis-acting RNA elements have been observed within the HPV-16 late region which may be involved in control of capsid gene expression. Mechanisms controlling HPV-16 capsid gene expression and the cellular RNA-processing factors involved will be the focus of this article.