Nuclear Matrix Attachment Regions of Human Papillomavirus Type 16 Point toward Conservation of These Genomic Elements in All Genital Papillomaviruses

Abstract

The gene functions, transcriptional regulation, and genome replication of human papillomaviruses (HPVs) have been extensively studied. Thus far, however, there has been little research on the organization of HPV genomes in the nuclei of infected cells. As a first step to understand how chromatin and suprachromatin structures may modulate the life cycles of these viruses, we have identified and mapped interactions of HPV DNAs with the nuclear matrix. The endogenous genomes of HPV type 16 (HPV-16) which are present in SiHa, HPKI, and HPKII cells, adhere in vivo to the nuclear matrixes of these cell lines. A tight association with the nuclear matrix in vivo may be common to all genital HPV types, as the genomes of HPV-11, HPV-16, HPV-18, and HPV-33 showed high affinity in vitro to preparations of the nuclear matrix of C33A cells, as did the well-known nuclear matrix attachment region (MAR) of the cellular beta interferon gene. Affinity to the nuclear matrix is not evenly spread over the HPV-16 genome. Five genomic segments have strong MAR properties, while the other parts of the genome have low or no affinity. Some of the five MARs correlate with known cis -responsive elements: a strong MAR lies in the 5′ segment of the long control region (LCR), and another one lies in the E6 gene, flanking the HPV enhancer, the replication origin, and the E6 promoter. The strongest MAR coincides with the E5 gene and the early-late intergenic region. Weak MAR activity is present in the E1 and E2 genes and in the 3′ part of L2. The in vitro map of MAR activity appears to reflect MAR properties in vivo, as we found for two selected fragments with and without MAR activity. As is typical for many MARs, the two segments with highest affinity, namely, the 5′ LCR and the early-late intergenic region, have an extraordinarily high A-T content (up to 85%). It is likely that these MARs have specific functions in the viral life cycle, as MARs predicted by nucleotide sequence analysis, patterns of A-T content, transcription factor YY1 binding sites, and likely topoisomerase II cleavage sites are conserved in similar positions throughout all genital HPVs.