The expression frequency of common fragile sites and genetic predisposition to colon cancer

Positioning of cervical carcinoma and Burkitt lymphoma translocation breakpoints with respect to the human papillomavirus integration cluster in FRA8C at 8q24.13

Molecular cytogenetic analysis frequently shows human papillomavirus (HPV) integration near translocation breakpoints in cervical cancer cells. We have recently described a cluster of HPV18 integrations in the distal end of the common fragile site FRA8C at 8q24 in primary cervical carcinoma samples. Chromosome band 8q24 contains the MYC gene (alias c-MYC), FRA8C, and FRA8D. The MYC gene is frequently deregulated--usually by translocation or amplification--in various tumor types. In the present study, we performed a molecular cytogenetic analysis of HPV18 integration patterns and the 8q24 translocation in a primary cervical carcinoma and in HeLa cells using combined binary ratio-fluorescence in situ hybridization. Our aim was to determine how the chromosomal breaks involved in these events relate physically to the MYC gene; whether they map to the FRA8C site, the FRA8D site, or both; and how they correlate with the occurrence of DNA flexibility domains. The 8q24 translocation breakpoints mapped between stretches of integrated HPV18 sequences in the distal end of FRA8C. This region contained DNA helix flexibility clusters, several of which mapped in the vicinity of HPV integration sites and translocation breakpoints in cervical carcinomas. DNA helix flexibility clusters were also found near known MYC translocation breakpoints in Burkitt lymphomas (BL), but most BL breakpoints mapped clearly outside FRA8C. Our data revealed that FRA8C is involved in HPV integration and chromosomal translocations in cervical carcinoma; however, this fragile site is not involved in classical MYC translocations in most BLs. In the context of the familial nature of cervical cancer, FRA8C may be considered a candidate susceptibility region for cervical carcinoma.

Investigation of the genotoxic effect in bone marrow of Swiss albino mice exposed long-term to pyrimethamine

In the present study, we investigated the genotoxic effect of pyrimethamine, which is a drug used in the therapy of toxoplasmosis and malaria, in bone marrow cells of Swiss albino mice exposed to three doses (1, 4, 8 mg/kg) of this agent for eight months orally in vivo. We used a chromosome analysis and micronucleus test for evaluation of genotoxic effect. While a statistically significant change was not determined in numerical chromosome abnormalities, structural chromosome aberrations and micronuclei were increased in a dose-dependent manner by cytogenetic and statistical evaluations.

Cloning and characterization of the common fragile site FRA6F harboring a replicative senescence gene and frequently deleted in human tumors

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.

Investigation of genetic susceptibility to non-small cell lung cancer by fragile site expression

Fragile sites are non-staining gaps and breaks in specific points of chromosomes that are inducible by various culture conditions. Previous studies have shown that various clastogenic agents increase expression of fragile sites. In this study, the expression of common fragile sites induced by aphidicolin was evaluated on prometaphase chromosomes obtained from peripheral blood lymphocytes. Chromosomal aberrations and fragile site expression of 60 individuals, including 20 patients with non-small cell lung cancer (NSCLC), 20 of their clinically healthy family members, and 20 age-matched normal healthy controls without history of any cancer type were studied. Both the proportion of damaged cells (P < 0.001) and the mean number of gaps and breaks per cell (P < 0.001) were significantly higher in both the patients and relatives' groups when compared with the control group. However, they were insignificant when the patients were compared to their relatives (P > 0.05). We determined four aphidicolin type common fragile sites in our study. These sites in patients with NSCLC and relatives were the following: 1p21, 2q33, 3p14, and 16q23. In these fragile sites, 2q33, 3p14, and 16q23 sites were statistically significant when compared with control group (P < 0.001, P < 0.0005, and P < 0.05, respectively). Consequently, we believe that fragile site studies may be helpful to detection of cancer risk.

Chromosomal fragile sites and relationship between genetic predisposition to small cell lung cancer

Fragile sites are non-staining gaps and breaks on mammalian chromosomes. Several investigators have pointed out that these sites may act as factors that predispose to specific chromosomal rearrangements that are present in some cancer cases. The expression of common fragile sites induced by aphidicolin (Apc) was evaluated on prometaphase chromosomes obtained from the peripheral blood lymphocytes of 15 patients with lung cancer, 20 of their clinically healthy family members, and 20 age-matched normal controls. As a result of cytogenetic evaluation carried out by the High Resolution Banding (HRB) technique, 1q21, 2q33, 3p14, 7q32, 13q13, 16q23, 17q21, and 22q12 are defined as fragile sites in patients and relatives. The rate of total fragile sites and 2q33, 3p14, and 16q23 are statistically significant in both patients and relatives when compared with the control group. Therefore, our results showed that common fragile sites might be unstable factors in the human genome and they can be used as suitable markers for genetic predisposition to lung cancer.