Sister chromatid exchange frequency in breast cancer cases

Recombination Mediator Proteins: Misnomers That Are Key to Understanding the Genomic Instabilities in Cancer

Recombination mediator proteins have come into focus as promising targets for cancer therapy, with synthetic lethal approaches now clinically validated by the efficacy of PARP inhibitors in treating BRCA2 cancers and RECQ inhibitors in treating cancers with microsatellite instabilities. Thus, understanding the cellular role of recombination mediators is critically important, both to improve current therapies and develop new ones that target these pathways. Our mechanistic understanding of BRCA2 and RECQ began in Escherichia coli. Here, we review the cellular roles of RecF and RecQ, often considered functional homologs of these proteins in bacteria. Although these proteins were originally isolated as genes that were required during replication in sexual cell cycles that produce recombinant products, we now know that their function is similarly required during replication in asexual or mitotic-like cell cycles, where recombination is detrimental and generally not observed. Cells mutated in these gene products are unable to protect and process replication forks blocked at DNA damage, resulting in high rates of cell lethality and recombination events that compromise genome integrity during replication.

Increased sister chromatid exchange frequency in young women with breast cancer and in their first-degree relatives

The well-known increased risk of breast cancer (BC) in first-degree relatives of patients with BC has been related to shared genetic factors including defective DNA repair, with loss of genomic integrity. On the other hand, it can be hypothesized that early-onset breast cancer is also associated with overburden of heritable factors leading to increased DNA injury. In this respect, we analyzed sister chromatid exchange frequency (SCE) in 20 women with breast cancer (all < or =40 years old), in their first-degree female relatives, and in 20 age-matched healthy females without a personal or family history of cancer. SCE was significantly increased (P < 0.05) in patients (7.17 +/- 1.81 per metaphase) and in their first-degree relatives (6.44 +/- 0.98), compared with controls (5.85 +/- 0.72). There was no difference in SCE frequency between patients and their first-degree relatives. We suggest that the increased SCE in patients reflects a genomic instability that may be operative in carcinogenesis. Further, genomic instability is shared also by first-degree relatives, although none of them had a history of breast cancer at the time of the study.

When replication travels on damaged templates: bumps and blocks in the road

Escherichia coli can accurately replicate their genome even when it contains hundreds of damaged bases. In this situation, processes such as DNA repair, translesion DNA synthesis, and recombination all contribute to the cell's ability to successfully complete this task. However, under conditions when these reactions go awry, these same processes can result in cell lethality, mutagenesis, or genetic instability. In order to understand the molecular events that can lead this normally faithful duplication of the genome to become less than perfect, it is essential to define the substrates and conditions when each of these processes are recruited to the replication fork.

Status of chromosome breaks and gaps in breast cancer. a follow-up study

Genetic susceptibility and environmental factors are believed to be responsible for chromosomal instabilities and higher incidence of breast cancer. We conducted a follow-up study to find the levels of chromosome breaks and gaps in 20 premenopausal women with breast cancer before surgery, 1 month after surgery, and 3 years after surgery with respect to 20 age- and gender-matched controls. The mean level of chromosome breaks and gaps was found to be significantly higher (P<0.001) in breast cancer patients (before surgery) as compared with the controls. The chromosome breaks and gaps after 1 month of surgery were observed significantly decreased (P<0.005) when compared with that of patients before the surgery. Further significant increase in chromosome breaks and gaps was found after 3 years of surgery as compared with both the patients after 1 month of surgery (P<0.05) and controls (P<0.005). The significant increase in chromosome breaks and gaps in breast cancer patients (before surgery) may be due to the effects of genetic susceptibility to environmental carcinogens and endogenous factors. However, the decrease in this level after 1 month of surgery may be due to the removal of cancerous tissues, which in turn removes the effect of mutagens and clastogenic factors. Further increase in chromosome breaks and gaps after 3 years of surgery may be due to the long-term effects of therapeutic agents and genetic susceptibility to environmental carcinogens in the patients. The study furthermore suggests that the high level of chromosome breaks and gaps after 3 years of surgery may be a risk factor for the development of secondary tumor in patients.

Participation of recombination proteins in rescue of arrested replication forks in UV-irradiated Escherichia coli need not involve recombination

Alternative reproductive cycles make use of different strategies to generate different reproductive products. In Escherichia coli, recA and several other rec genes are required for the generation of recombinant genomes during Hfr conjugation. During normal asexual reproduction, many of these same genes are needed to generate clonal products from UV-irradiated cells. However, unlike conjugation, this latter process also requires the function of the nucleotide excision repair genes. Following UV irradiation, the recovery of DNA replication requires uvrA and uvrC, as well as recA, recF, and recR. The rec genes appear to be required to protect and maintain replication forks that are arrested at DNA lesions, based on the extensive degradation of the nascent DNA that occurs in their absence. The products of the recJ and recQ genes process the blocked replication forks before the resumption of replication and may affect the fidelity of the recovery process. We discuss a model in which several rec gene products process replication forks arrested by DNA damage to facilitate the repair of the blocking DNA lesions by nucleotide excision repair, thereby allowing processive replication to resume with no need for strand exchanges or recombination. The poor survival of cellular populations that depend on recombinational pathways (compared with that in their excision repair proficient counterparts) suggests that at least some of the rec genes may be designed to function together with nucleotide excision repair in a common and predominant pathway by which cells faithfully recover replication and survive following UV-induced DNA damage.

Fluorescent in situ hybridization assessment of chromosome 8 copy number in breast cancer

Conventional cytogenetics of breast and other solid tumors has been hampered by a number of factors. An analysis of breast tumor tissues was therefore undertaken using fluorescent in situ hybridization (FISH). A total of 34 specimens were analyzed using a chromosome 8-specific alpha-satellite probe. Various approaches were tested and compared. Among 30 informative samples, 11 infiltrating ductal carcinomas, not otherwise specified (NOS), 5 ductal carcinomas in situ, 5 lobular carcinomas, 3 papillary carcinomas, and 6 benign lesions were studied. Of the 11 cases of infiltrating ductal carcinomas (NOS) analyzed, four cases showed 3 signals, one case showed 4 signals, and the rest showed 2 signals. Of the 5 cases of ductal carcinoma in situ samples, 1 showed 3 signals and the other 4 cases showed 2 signals. All cases of lobular carcinomas, papillary carcinomas, and benign lesions showed 2 signals. We inferred from these data that 36% of the infiltrating ductal carcinomas (NOS) were trisomic and 9% were tetrasomic, whereas 20% of the ductal carcinomas in situ were trisomic. All samples from lobular carcinomas, papillary carcinomas, and the benign lesions were disomic. From our preliminary data, it can further be concluded that a subset of breast cancer is characterized by chromosome 8 trisomy. These data are consistent with an ever-increasing database on the association of chromosomal 8 trisomy with other cancers such as leukemia, lymphoma, prostate cancer, ovarian carcinoma, salivary gland tumor, malignant melanoma, desmoid tumors, and recently gestational trophoblastic disease. It is also noted that the ability to analyze formalin-fixed, paraffin-embedded archival material will enable a more comprehensive cytogenetic study of breast cancer than is currently available.

Choromosome instabililty and sister chromatid exchange (SCE) studies in patients with carcinoma of cervix uteri

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 14 patients with carcinoma of the cervix uteri. Simultaneously, sister chromatid exchange (SCE) was also analyzed in the peripheral blood lymphocytes of these patients, along with those of 20 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with carcinoma of the cervix uteri (7.85%) than in the age-matched controls (3.35%). A large number of chromosome aberrations in lymphocytes of these patients have also been detected. Sister chromatid exchange (SCE) was also analyzed in lymphocytes of 14 patients with carcinoma of the cervix uteri and 20 age-matched control subjects. The mean SCE frequencies were 9.44 +/- 0.34 (n = 637) and 6.09 +/- 0.24 (n = 900) per metaphase in patients and controls, respectively. The increase of SCE frequency in cancer patients was statistically significant (p < 0.001), but not seen in controls. Our results suggest that patients with carcinoma of the cervix uteri show a degree of chromosomal instability that might be related to a predisposition to neoplasia.

Nuclear lesions during rat hepatocarcinogenesis. I. Measuring the sister-chromatid exchanges during initiation, promotion and progression of rat hepatocarcinogenesis induced with diethylnitrosamine

Cytogenetic endpoints such as sister-chromatid exchanges (SCEs), chromosomal aberrations and micronuclei (MNs) have been widely used as indicators of genetic damage. However, no systematic attempts have been made to correlate the levels of these cytogenetic endpoints with the different steps of carcinogenesis. In the present report, the induction, accumulation and persistence of SCEs and high frequency cells (HFCs) were measured in liver cells during the initiation, promotion and progression steps of rat hepatocarcinogenesis induced by diethylnitrosamine (DEN). The results indicate that lesions leading to SCEs accumulate during initiation only. When DEN administration is longer than the duration of this first step, SCE values stabilize. After stopping the carcinogenic treatment, the SCE levels decrease to control values whether or not promotion and progression occur.

Sister chromatid exchange (SCE) studies in breast cancer patients: a follow-up study

Sister chromatid exchanges (SCEs) were studied in 20 patients with breast cancer (stage II) before surgery, one month after surgery, and after three years as a follow-up study. Data from 50 age-matched, normal healthy females, preferably from the affected families, served as controls. In each patient, 50 well-spread metaphases were scored for SCEs. The mean values of SCEs per metaphase were 5.80, 4.69, and 5.98 in breast cancer patients before surgery, one month after surgery, and after a gap of three years as a follow-up, respectively. The one-way analysis of variance was applied and it was found that there was a highly significant difference in the frequency of sister chromatid exchanges in these patients before surgery, one month after surgical removal of cancerous tissue, and after three years as a follow-up study. The elevated level of SCEs three years after surgical removal of cancerous tissue predict the chances of development of another type of cancer.