Expression of HPV16 E6 or E7 increases integration of foreign DNA.
In most invasive cervical carcinomas, high-risk human papillomavirus (HPV) DNA is integrated into the host genome, while in pre-invasive cervical lesions the viral genome is typically maintained exclusively as an episome. In contrast, integration of low-risk HPV DNA is rare, as is the association of low-risk HPVs with carcinomas. High-risk HPV integration is associated with a selective growth advantage of affected cells, and hence, integration is likely to be an important genetic alteration contributing to cervical tumor progression. Expression of high-risk, but not low-risk, HPV E6 or E7 proteins disrupts the p53-dependent G1 arrest that cells normally display in response to DNA damage. Absence of this cell cycle checkpoint may predispose cells containing high-risk HPVs to genetic instability and to the accumulation of the genetic alterations that appear to be required for HPV-associated cervical tumor progression. We hypothesized that integration of high-risk HPV DNA into the host cell genome may be facilitated by E6- and/or E7-mediated disruption of the normal DNA damage response pathway. To test this hypothesis, we assessed the integration frequency of a reporter plasmid (pHyGal) in RKO cells expressing individual E6 or E7 genes of either high-risk (HPV16) or low-risk (HPV6, HPV11) type viruses. Cells expressing HPV16 E6 or HPV16 E7 exhibited a significantly increased frequency of pHyGal integration in comparison to RKO control cells or cells expressing low-risk HPV E6 or E7. Thus, expression of high-risk, but not low-risk, E6 and E7 proteins increases the frequency of foreign DNA integration into the host genome. These findings suggest that at least some of the difference in oncogenic potential observed between high-risk and low-risk HPV types may be determined by the increased ability of high-risk HPVs to integrate into host DNA.
Kessis
T D
TD
Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2196, USA.
Connolly
D C
DC
Hedrick
L
L
Cho
K R
KR
D002934:Cinnamates; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism*; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000235:genetics* / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics* / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D006921:Hygromycin B / Q000031:analogs & derivatives / Q000494:pharmacology; D009856:Oncogene Proteins, Viral / Q000096:biosynthesis* / Q000235:genetics; D050725:Papillomavirus E7 Proteins; D010957:Plasmids; D012097:Repressor Proteins; D014162:Transfection; D014407:Tumor Cells, Cultured; D016662:Virus Integration; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D002934:Cinnamates; D004273:DNA, Neoplasm; D004279:DNA, Viral; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D006921:Hygromycin B; C026273:hygromycin A; D001616:beta-Galactosidase