Mechanism of genomic instability in cells infected with the high-risk human papillomaviruses

Autor: Triin Laos, Mart Ustav, Ene Ustav, Helen Isok-Paas, Meelis Kadaja
Jazyk: angličtina
Rok vydání: 2009
Předmět:
Zdroj: PLoS Pathogens, Vol 5, Iss 4, p e1000397 (2009)
PLoS Pathogens
ISSN: 1553-7374
1553-7366
Popis: In HPV–related cancers, the “high-risk” human papillomaviruses (HPVs) are frequently found integrated into the cellular genome. The integrated subgenomic HPV fragments express viral oncoproteins and carry an origin of DNA replication that is capable of initiating bidirectional DNA re-replication in the presence of HPV replication proteins E1 and E2, which ultimately leads to rearrangements within the locus of the integrated viral DNA. The current study indicates that the E1- and E2-dependent DNA replication from the integrated HPV origin follows the “onion skin”–type replication mode and generates a heterogeneous population of replication intermediates. These include linear, branched, open circular, and supercoiled plasmids, as identified by two-dimensional neutral-neutral gel-electrophoresis. We used immunofluorescence analysis to show that the DNA repair/recombination centers are assembled at the sites of the integrated HPV replication. These centers recruit viral and cellular replication proteins, the MRE complex, Ku70/80, ATM, Chk2, and, to some extent, ATRIP and Chk1 (S317). In addition, the synthesis of histone γH2AX, which is a hallmark of DNA double strand breaks, is induced, and Chk2 is activated by phosphorylation in the HPV–replicating cells. These changes suggest that the integrated HPV replication intermediates are processed by the activated cellular DNA repair/recombination machinery, which results in cross-chromosomal translocations as detected by metaphase FISH. We also confirmed that the replicating HPV episomes that expressed the physiological levels of viral replication proteins could induce genomic instability in the cells with integrated HPV. We conclude that the HPV replication origin within the host chromosome is one of the key factors that triggers the development of HPV–associated cancers. It could be used as a starting point for the “onion skin”–type of DNA replication whenever the HPV plasmid exists in the same cell, which endangers the host genomic integrity during the initial integration and after the de novo infection.
Author Summary High-risk human papillomavirus infection can cause several types of cancers. During the normal virus life cycle, these viruses maintain their genomes as multicopy nuclear plasmids in infected cells. However, in cancer cells, the viral plasmids are lost, which leaves one of the HPV genomes to be integrated into the genome of the host cell. We suggest that the viral integration and the coexistence of episomal and integrated HPV genomes in the same cell play key roles in early events that lead to the formation of HPV–dependent cancer cells. We show that HPV replication proteins expressed at the physiological level from the viral extrachromosomal genome are capable of replicating episomal and integrated HPV simultaneously. Unscheduled replication of the integrated HPV induces a variety of changes in the host genome, such as excision, repair, recombination, and amplification, which also involve the flanking cellular DNA. As a result, genomic modifications occur, which could have a role in reprogramming the HPV–infected cells that leads to the development of cancer. We believe that the mechanism described in this study may reflect the underlying processes that take place in the genome of the HPV–infected cells and may also play a role in the formation of other types of cancers.
Databáze: OpenAIRE
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