Search

The development of cervical cancer is highly associated with human papillomavirus (HPV) infection. Greater than 99% of all cervical tumors contain HPV DNA. Integration of high-risk HPV has been temporally associated with the acquisition of a malignant phenotype. Recent work from our lab has shown that HPV16, the most common high-risk HPV associated with cervical carcinoma, preferentially integrates at loci containing human common fragile sites (CFSs). CFSs are regions of genomic instability that have also been associated with deletions, translocations, and gene amplification during cancer development. The current work shows that HPV18, the second most prevalent high-risk HPV type found in cervical tumors, preferentially targets the CFSs. We identified 27 unique HPV18 integrations in cervical tumors, of which 63% (P

Chronic infections with the hepatitis B virus (HBV) and high-risk human papillomaviruses (HPVs) are important risk factors for hepatocellular carcinoma (HCC) and cervical cancer (CC), respectively. HBV and HPV are DNA viruses that almost invariably integrate into the host genome in invasive tumors. The viral integration sites occur throughout the genome, leading to the presumption that there are no preferred sites of integration. A number of viral integrations have been shown to occur within the vicinity of important cancer-related genes. In studies of HBV-induced HCC and HPV-induced CC, we have identified two HBV and three HPV integrations into the human telomerase reverse transcriptase (hTERT) gene. Detailed characterization of the integrations revealed that four integrations occurred within the hTERT promoter and upstream region and the fifth integration occurred in intron 3 of the hTERT gene. None of the integrations altered the hTERT coding sequence and all resulted in juxtaposition of viral enhancers near hTERT, with potential activation of hTERT expression. Our work supports the hypothesis that the sites of oncogenic viral integration are nonrandom and that genes at the sites of viral integration may play important roles in carcinogenesis.

The development of cervical cancer is highly associated with human papillomavirus (HPV) infection. HPV integration into the genome of infected cervical cells is temporally associated with the acquisition of the malignant phenotype. A relationship between the sites of HPV integration in cervical cancer and the position of the common fragile sites (CFSs) has been observed at both the cytogenetic and molecular levels. To further explore this relationship at the molecular level, we used RS-PCR to rapidly isolate cellular sequences flanking the sites of HPV16 integration in 26 primary cervical tumors. Human bacterial artificial chromosome clones were isolated based on these flanking sequences and used as probes for fluorescence in situ hybridization on aphidicolin-stimulated metaphases. Our data demonstrate that 11/23 HPV16 integrations in cervical tumors occurred within CFSs (P&

FRA3B is the most frequently expressed common fragile site localized within human chromosomal band 3p14.2, which is frequently deleted in many different cancers, including cervical cancer. Previous reports indicate aphidicolin-induced FRA3B instability occurs over approximately 500 kb which is spanned by the 1.5 Mb fragile histidine triad (FHIT) gene. Recently an HPV16 cervical tumor integration, 2 Mb centromeric to the published FRA3B region, has been identified. FISH-based analysis with a BAC spanning the integration has demonstrated this integration occurs within the FRA3B region of instability. These data suggest that the unstable FRA3B region is much larger than previously reported. FISH-based analysis of aphidicolin-induced metaphase chromosomes allowed for a complete characterization of instability associated with FRA3B. This analysis indicates that fragility extends for 4 Mb. Within this region are a total of five genes, including FHIT. FRA3B gene expression analysis on a panel of cervical tumor-derived cell lines revealed that three of the five genes within FRA3B were aberrantly regulated. A similar analysis of genes outside of FRA3B indicated that the surrounding genes were not aberrantly expressed. These data provide additional support that regions of instability associated with CFSs and the genes contained within them, may play an important role in cancer development.

The common fragile site FRA6F, located at 6q21, is an extended region of about 1200 kb, with two hot spots of breakage each spanning about 200 kb. Transcription mapping of the FRA6F region identified 19 known genes, 10 within the FRA6F interval and nine in a proximal or distal position. The nucleotide sequence of FRA6F is rich in repetitive elements (LINE1 and LINE2, Alu, MIR, MER and endogenous retroviral sequences) as well as in matrix attachment regions (MARs), and shows several DNA segments with increased helix flexibility. We found that tight clusters of stem-loop structures were localized exclusively in the two regions with greater frequency of breakage. Chromosomal instability at FRA6F probably depends on a complex interaction of different factors, involving regions of greater DNA flexibility and MARs. We propose an additional mechanism of fragility at FRA6F, based on stem-loop structures which may cause delay or arrest in DNA replication. A senescence gene likely maps within FRA6F, as suggested by detection of deletion and translocation breakpoints involving this fragile site in immortal human-mouse cell hybrids and in SV40-immortalized human fibroblasts containing a human chromosome 6 deleted at q21. Deletion breakpoints within FRA6F are common in several types of human leukemias and solid tumors, suggesting the presence of a tumor suppressor gene in the region. Moreover, a gene associated to hereditary schizophrenia maps within FRA6F. Therefore, FRA6F may represent a landmark for the identification and cloning of genes involved in senescence, leukemia, cancer and schizophrenia.