BRCA1 Pathway Function in Basal-Like Breast Cancer Cells

Sporadic basal-like cancers (BLCs) are a common subtype of breast cancer that share multiple biological properties with BRCA1-mutated breast tumors. Despite being BRCA1^+/+, sporadic BLCs are widely viewed as phenocopies of BRCA1-mutated breast cancers, because they are hypothesized to manifest a BRCA1 functional defect or breakdown of a pathway(s) in which BRCA1 plays a major role. The role of BRCA1 in the repair of double-strand DNA breaks by homologous recombination (HR) is its best understood function and the function most often implicated in BRCA1 breast cancer suppression. Therefore, it is suspected that sporadic BLCs exhibit a defect in HR. To test this hypothesis, multiple DNA damage repair assays focused on several types of repair were performed on a group of cell lines classified as sporadic BLCs and on controls. The sporadic BLC cell lines failed to exhibit an overt HR defect. Rather, they exhibited defects in the repair of stalled replication forks, another BRCA1 function. These results provide insight into why clinical trials of poly(ADP-ribose) polymerase (PARP) inhibitors, which require an HR defect for efficacy, have been unsuccessful in sporadic BLCs, unlike cisplatin, which elicits DNA damage that requires stalled fork repair and has shown efficacy in sporadic BLCs.     

Anaerobic dechlorination of perchloroethene in an extractive membrane bioreactor

An extractive membrane bioreactor (EMB) is described that used an undefined anaerobic culture to dechlorinate tetrachloroethene (C₂Cl₄) reductively in a synthetic wastewater. Comparable reactors described in the literature use set-ups where the bacteria are in direct contact with the wastewater, and thus would require the addition of significant quantities of nutrients to the wastewater stream in practical application. In the EMB, a silicone rubber membrane separates the microbial culture from the wastewater stream, so that addition of nutrients can be minimised. The EMB was operated continuously for 48 days and dechlorinated 359 mol C₂Cl₄/(l biomedium⁻¹ day⁻¹) on average. Lactate was fed as an electron donor and C₂Cl₄ dechlorination was verified by chloride measurements. Particular attention was paid to the reduction of transmembrane C₂Cl₄ flux caused by a membrane-attached biofilm. Following a start-up period, the reactor operation was stable and remained largely unaffected by biofilm thickness and oxygen contamination from the wastewater. Received: 19 January 1998 / Received revision: 8 May 1998 / Accepted: 8 May 1998     

Membrane transport of potassium ions in erythrocytes of the American black bear, Ursus americanus

1. Membrane transport of K ions was investigated in red blood cells of bears by methods of measurement of unidirectional isotopic fluxes. 2. Unlike red cells of dogs, red cells of bears exhibited a significant, though small, component of ouabain-sensitive K influx. 3. Ouabain-insensitive K influx, as in other carnivore cells, was activated by swelling and inhibited by shrinkage. Swelling-induced K influx was dependent upon presence of chloride ions but was not inhibited by furosemide or bumetanide. 4. Ouabain-sensitive K influx was largest with ATP and with high concentration of Na in the cell, but it persisted in the absence of cytoplasmic Na or ATP. It was also resistant to the drug, harmaline, at a concentration that in other cells fully inhibits ouabain-sensitive K influx. 5. It was concluded that under such adverse conditions ouabain-sensitive K influx represents another mode of the Na/K pump not fully described elsewhere. 6. Also, as in low K red cells of sheep and goat, apparent absence of Na/K pump activity in carnivore red cells may represent suppression rather than elimination of activity. 7. Ouabain-insensitive K influx showed a seasonal pattern with minima occurring in early winter, earlier than for the minimum observed in Na influx. 8. Ouabain-sensitive K influx tended to be lower in the hibernation season of the bear, but the seasonal pattern was not consistent.     

Localization of the simian virus 40 small t antigen in the nucleus and cytoplasm of monkey and mouse cells.

Monkey and mouse cells producing simian virus 40 small t antigen in the absence of clearly detectable intact or truncated large T antigens were subjected to indirect immunofluorescence and biochemical cell compartment analyses. Results revealed specific immunofluorescence and small t polypeptide in both the nucleus and cytoplasm of these cells.     

Production of active single-chain antibodies in seeds using trimeric polyoleosin fusion

A variety of single-chain variable fragments (scFv) that had been previously developed to the surface epitopes of infective Trichostrongylus colubriformis L3 pathogenic gut nematodes of sheep were fused to a trimeric version of polyoleosin (three head-to-tail repeats of oleosin) and expressed in planta under the control of an Arabidopsis oleosin promoter. The fusion products were found to accumulate in oil bodies (OBs) at the range of 0.25-0.9% of the total seed protein which is comparable with the main 18kDa isoform of Arabidopsis seed oleosin. Immunofluorescence microscopy and immuno-binding were used to demonstrate that it is possible to both purify the recombinant protein via enrichment for OBs as well as use the OBs emulsion to deliver functional recombinant scFv. This work presents a novel fusion strategy platform to boost the productivity and simplify the delivery of recombinant single chain antibodies and other like proteins.     

Medical students in community physicians' offices

Can the medical student benefit from spending time in the offices of community physicians? Eight consecutive final-year medical students visited the offices of 39 physicians, 31 family physicians and eight specialists, in the communities of Richmond and Delta, British Columbia. The students describe the value of their experience, common problems seen, continuity of care, practice variation, opportunities in specialist office practice and the standard of practice observed. We strongly suggest that some medical student instruction must take place in the community to ensure improved patient care from doctors with a reality-based training. All students, whatever their eventual area of work, would benefit from this experience and we recommend that other centres try similar experiments.