Do dogs harbour risk factors for human breast cancer?

We ask consulting patients regularly whether they keep pets in order to identify zoonotic factors. It became apparent that patients with breast carcinoma (N=69) owned significantly more often dogs but not cats compared to age matched female controls. We compared the frequencies of dog and pet ownership with data from public available statistics on women (N=1320) of the same age group in Bavaria. The most striking result was that more than twice the number of patients kept dogs permanently in the last 10 years and at the time of interrogation as compared to control individuals at the time of interrogation (p=0.0000003, relative risk 3.5). Further internet search on the morbidity of breast carcinoma showed in dogs a protracted course of disease and metastases into lung, liver and bones, resembling the course of disease in human breast cancer. In contrast with this, breast cancer presented in cats a dramatically short course and the main but unusual location of metastasis presents in the hind legs. A recent publication in Norway reported on a high frequency (53.3%) of breast carcinomas in 14,401 investigated dogs. Which transmissible factor or factors come into question? Variants of the mouse mammary tumor virus (MMTV) can productively replicate in human cells and in different animals, including dogs. Many investigators, but not all, could identify MMTV-like sequences in sporadic human breast cancer. MMTV or MMTV-like sequences have not been investigated in canine breast carcinomas until now. It is also conceivable that other microbes from the dog, for example bacteria, could participate in the first steps of carcinogenesis in human. It was recently shown that bartonella species promote vascularization and prevent apoptosis of infected cells with the same methods as helicobacter pylori. Our considerations require further research. Epidemiologic cohort studies and identification of potential carcinogenic microbial factors will prove or disprove our hypothesis that risk factors from dogs could contribute to the carcinogenesis of human breast cancer.

Subtelomeric repeat amplification is associated with growth at elevated temperature in yku70 mutants of Saccharomyces cerevisiae.

Inactivation of the Saccharomyces cerevisiae gene YKU70 (HDF1), which encodes one subunit of the Ku heterodimer, confers a DNA double-strand break repair defect, shortening of and structural alterations in the telomeres, and a severe growth defect at 37 degrees. To elucidate the basis of the temperature sensitivity, we analyzed subclones derived from rare yku70 mutant cells that formed a colony when plated at elevated temperature. In all these temperature-resistant subclones, but not in cell populations shifted to 37 degrees, we observed substantial amplification and redistribution of subtelomeric Y' element DNA. Amplification of Y' elements and adjacent telomeric sequences has been described as an alternative pathway for chromosome end stabilization that is used by postsenescence survivors of mutants deficient for the telomerase pathway. Our data suggest that the combination of Ku deficiency and elevated temperature induces a potentially lethal alteration of telomere structure or function. Both in yku70 mutants and in wild type, incubation at 37 degrees results in a slight reduction of the mean length of terminal restriction fragments, but not in a significant loss of telomeric (C(1-3)A/TG(1-3))(n) sequences. We propose that the absence of Ku, which is known to bind to telomeres, affects the telomeric chromatin so that its chromosome end-defining function is lost at 37 degrees.

Radiation-induced chromosome aberrations in Saccharomyces cerevisiae: influence of DNA repair pathways.

Radiation-induced chromosome aberrations, particularly exchange-type aberrations, are thought to result from misrepair of DNA double-strand breaks. The relationship between individual pathways of break repair and aberration formation is not clear. By electrophoretic karyotyping of single-cell clones derived from irradiated cells, we have analyzed the induction of stable aberrations in haploid yeast cells mutated for the RAD52 gene, the RAD54 gene, the HDF1(= YKU70) gene, or combinations thereof. We found low and comparable frequencies of aberrational events in wildtype and hdf1 mutants, and assume that in these strains most of the survivors descended from cells that were in G2 phase during irradiation and therefore able to repair breaks by homologous recombination between sister chromatids. In the rad52 and the rad54 strains, enhanced formation of aberrations, mostly exchange-type aberrations, was detected, demonstrating the misrepair activity of a rejoining mechanism other than homologous recombination. No aberration was found in the rad52 hdf1 double mutant, and the frequency in the rad54 hdf1 mutant was very low. Hence, misrepair resulting in exchange-type aberrations depends largely on the presence of Hdf1, a component of the nonhomologous end-joining pathway in yeast.

Phagocytic killing of microorganisms by radical processes: consequences of the reaction of hydroxyl radicals with chloride yielding chlorine atoms.

Chloride anions and hydrogen peroxide serve as substrates for myeloperoxidase (MPO) in order to produce hypochlorous acid (HOCl) as one of the major killing agents of phagocytic leukocytes. Apart from this role of being a substrate for the MPO-reaction the chloride anion has been considered as unreactive and has not been implicated in radical reactions which contribute to the killing process. From the inherent reactivities of the pertinent radicals (as determined by pulse radiolysis experiments), the great abundance of chloride, and the most probable distribution of reactants within the phagosome, we deduce estimates for the average life-time and free diffusion path-length in this milieu and arrive at a model according to which chloride ions enter into radical chains and influence the killing of ingested bacteria to an extraordinarily high extent. We propose that hydroxyl radicals--despite some controversial arguments in the literature--may still be considered as important contributors to cell killing especially since we show that their reactions are made more effective by producing chlorine radicals in a cyclic process. We furthermore present arguments how the phagocyte may protect itself from harmful actions of HOCl and H2O2 after the superoxide-generating activity of NADPH oxidase is turned off.

Hydrogen peroxide protects yeast cells from inactivation by ionizing radiation: a radiobiological paradox.

PURPOSE: To elucidate mechanisms of the interaction of hydrogen peroxide with chloride-derived cytotoxins under steady-state irradiation conditions and to determine the effects on cell viability. MATERIALS AND METHODS: Yeast cells were suspended in phosphate-buffered saline and exposed to 60Co gamma-irradiation under different conditions. The colony-forming ability was determined. RESULTS: Irradiation of PBS produces H2O2 and HOCl simultaneously. Under slightly acidic conditions and low oxygen tension the yield of HOCl exceeds that of H2O2 while at physiological pH and normoxic conditions H2O2 exceeds HOCl. Both substances react with each other rapidly in a pH-dependent way, even during an irradiation that lasts several seconds. As HOCl is about 1000-fold more toxic than H2O2 to the strain of Saccharomyces cerevisiae used in these experiments, it is evident that in an irradiation that produces more HOCl than H2O2 the radiation-induced damage will be large. If, in contrast, the cells are irradiated under conditions in which H2O2 production predominates, the damage will be small. One would therefore predict that addition of hydrogen peroxide to a cell suspension prior to irradiation should result in protection for suspended cells if H2O2 interferes with the generation of HOCl and thereby inactivates this more powerful toxin. Our data show that addition of H2O2 in sublethal concentration decreases radiation-induced cell death to the level that is found in chloride-free solution, i.e. depending on pH, reduces it by a factor of > or = 3.

Associations between Chlamydophila infections, schizophrenia and risk of HLA-A10.

Several microbes have been suspected as pathogenetic factors in schizophrenia. We have previously observed increased frequencies of chlamydial infections and of human lymphocyte antigen (HLA)-A10 in independent studies of schizophrenia. Our aim here was to analyze frequencies of three types of Chlamydiaceae in schizophrenic patients (n=72), random controls (n=225) and hospital-patient controls (n=36), together with HLA-A genotypes. Patients were diagnosed with schizophrenia according to Diagnostic and Statistical Manual of Mental Disorders-IV. Blood samples were collected at the beginning of hospitalization and analyzed with Chlamydiaceae species-specific polymerase chain reaction (PCR). Control panels consisted of randomly selected volunteers and hospitalized, non-schizophrenic patients. We found chlamydial infection in 40.3% of the schizophrenic patients compared to 6.7% in the controls. The association of schizophrenia with Chlamydiaceae infections was highly significant (P=1.39 x 10(-10), odds ratio (OR)=9.43), especially with Chlamydophila psittaci (P=2.81 x 10(-7), OR=24.39). Schizophrenic carriers of the HLA-A10 genotype were clearly most often infected with Chlamydophila, especially C. psittaci (P=8.03 x 10(-5), OR=50.00). Chlamydophila infections represent the highest risk factor yet found to be associated with schizophrenia. This risk is even further enhanced in carriers of the HLA-A10 genotype.

Complex expression pattern of the TNF region gene LST1 through differential regulation, initiation, and alternative splicing.

Recently, a novel gene, LST1, was identified in the tumor necrosis factor region of the HLA complex, 4 kb centromeric of the lymphotoxin beta gene. By analyzing several full-length cDNA clones and the genomic DNA, we identified seven exons and four introns, spanning 2.7 kb. Isolation of mouse LST1 cDNA clones established the open reading frame. LST1 transcription is characterized by four alternative transcription initiation sites and extensive alternative splicing. The derived polypeptides vary with regard to the presence of the hydrophobic N-terminus and in short internal sequences. In addition, alternative splicing results in LST1 mRNAs encoding different carboxy-terminal sequences. LST1 is predominantly transcribed in monocytes, and mRNA levels increase upon stimulation with interferon-gamma, with a concomitant change in the mRNA pattern resulting in an enhanced expression of the short LST1 transcripts. These data suggest that LST1 may have a specific role in monocytes and possibly also in T cells. Moreover, we found that the recently published cDNA 1C7 is encoded just centromeric of LST1.