Human papillomavirus type 16 (HPV16) infects anogenital epithelia and is the etiological agent of cervical cancer. We showed previously that HPV16 infection regulates the key splicing/alternative splicing factor SF2/ASF and that virus late transcripts are extensively alternatively spliced. hnRNP A1 is the antagonistic counterpart of SF2/ASF in alternative splicing. We show here that hnRNP A1 is also up-regulated during differentiation of virus-infected epithelial cells in monolayer and organotypic raft culture. Taken together with our previous data on SF2/ASF, this comprises the first report of HPV-mediated regulation of expression of two functionally related cellular proteins during epithelial differentiation. Further, using electrophoretic mobility shift assays and UV crosslinking we demonstrate that hnRNP A1 binds the HPV16 late regulatory element (LRE) in differentiated HPV16 infected cells. The LRE has been shown to be important in temporally controlling virus late gene expression during epithelial differentiation. We suggest that increased levels of these cellular RNA processing factors facilitate appropriate alternative splicing necessary for production of virus late transcripts in differentiated epithelial cells.

HPV16 (human papillomavirus type 16) is a 7.9 kb double-stranded DNA virus that infects anogenital mucosal epithelia. In some rare cases, in women, infection can progress to cervical cancer. HPV16 gene expression is regulated through use of multiple promoters and alternative splicing and polyadenylation. The virus genome can be divided into an early and a late coding region. The late coding region contains the L1 and L2 genes. These encode the virus capsid proteins L1 and L2; protein expression is confined to the upper epithelial layers and is regulated post-transcriptionally in response to epithelial differentiation. A 79 nt RNA regulatory element, the LRE (late regulatory element), involved in this regulation is sited at the 3'-end of the L1 gene and extends into the late 3'-UTR (3'-untranslated region). This element represses late gene expression in differentiated epithelial cells and may activate it in differentiated cells. The present paper describes our current knowledge of LRE RNA-protein interaction and their possible functions.