Fission yeast 26S proteasome mutants are multi-drug resistant due to stabilization of the pap1 transcription factor

Here we report the result of a genetic screen for mutants resistant to the microtubule poison methyl benzimidazol-2-yl carbamate (MBC) that were also temperature sensitive for growth. In total the isolated mutants were distributed in ten complementation groups. Cloning experiments revealed that most of the mutants were in essential genes encoding various 26S proteasome subunits. We found that the proteasome mutants are multi-drug resistant due to stabilization of the stress-activated transcription factor Pap1. We show that the ubiquitylation and ultimately the degradation of Pap1 depend on the Rhp6/Ubc2 E2 ubiquitin conjugating enzyme and the Ubr1 E3 ubiquitin-protein ligase. Accordingly, mutants lacking Rhp6 or Ubr1 display drug-resistant phenotypes

Gene expression profiles derived from fine needle aspiration correlate with response to systemic chemotherapy in breast cancer

BACKGROUND: Drug resistance in breast cancer is a major obstacle to successful chemotherapy. In this study we used cDNA microarray technology to examine gene expression profiles obtained from fine needle aspiration (FNA) of primary breast tumors before and after systemic chemotherapy. Our goal was to determine the feasibility of obtaining representative expression array profiles from limited amounts of tissue and to identify those expression profiles that correlate with treatment response. METHODS: Repeat presurgical FNA samples were taken from six patients who were to undergo primary surgical treatment. Additionally, a group of 10 patients who were to receive neoadjuvant chemotherapy underwent two FNAs before chemotherapy (adriamycin 60 mg/m(2) and cyclophosphamide 600 mg/m(2)) followed by another FNA on day 21 after the first cycle. Total RNA was amplified with T7 Eberwine's procedure and labeled cDNA was hybridized onto a 7600-feature glass cDNA microarray. RESULTS: We identified candidate gene expression profiles that might distinguish tumors with complete response to chemotherapy from tumors that do not respond, and found that the number of genes that change after one cycle of chemotherapy was 10 times greater in the responding group than in the non-responding group. CONCLUSION: This study supports the suitability of FNA-derived cDNA microarray expression profiling of breast cancers as a comprehensive genomic approach for studying the mechanisms of drug resistance. Our findings also demonstrate the potential of monitoring post-chemotherapy changes in expression profiles as a measure of pharmacodynamic effect and suggests that these approaches might yield useful results when validated by larger studies

A study on the diffusion-induced grain boundary migration ahead of stress corrosion cracking crack tips through advanced characterization

Three austenitic alloys with different Ni content were stress corrosion cracking (SCC) tested in simulated pressurized water reactor (PWR) primary water at 320 and 360ºC. Diffusion-induced grain boundary migration (DIGM) associated with preferential intergranular oxidation (PIO) is observed ahead of all SCC crack tips. The occurrence of DIGM is revealed to be driven by PIO-induced diffusion of Cr, Fe, and Ni. The extent of DIGM is controlled by the lateral and in-depth elemental diffusion and PIO, with these processes interconnected. Temperature and alloy composition are revealed to affect the extent of DIGM by affecting these processes

A mechanistic study of SCC in Alloy 600 through high-resolution characterization

High-resolution characterization was used to understand the mechanisms controlling stress corrosion cracking (SCC) in Alloy 600 exposed to simulated PWR primary water conditions. Three potential active crack tips obtained from different types of grain boundaries were studied and compared. The results suggest that the dominant mechanism controlling SCC propagation is intergranular internal oxidation. The applied stress, pre-existent residual strain, the accumulation of defects around the crack tip, the formation of a Fe-Cr-depleted zone, and a porous intergranular oxide are acknowledged as necessary precursors to SCC. Based on the results obtained in this study, a model of SCC propagation is proposed

3D Atom-Probe Characterization of Stress and Cold-Work in Stress Corrosion Cracking of 304 Stainless Steel

Cold-worked 304 stainless steels (SS) are known to be susceptible to stress corrosion cracking (SCC). This study employs atom-probe tomography (APT) for local chemical analysis of the oxides formed. Autoclave experiments on a set of samples with/without cold-work prior to oxidation, and with/without stress applied during oxidation, were carried out under simulated pressurised water reactor (PWR) primary conditions. APT and analytical transmission electron microscopy (ATEM) were combined to investigate chemical and structural implications of surface and grain boundary oxidation in 304 SS. Focussed ion beam (FIB) milling was used to prepare specimens containing the same grain boundary for every analysis technique. Grain boundary and deformation band oxidation were observed in all but the unstressed and non-cold worked sample. Cavities were found ahead of the Cr-rich oxide in some of the samples. APT data suggests the presence of hydrogen in Nickel-rich regions

Observation and quantification of the diffusion-induced grain boundary migration ahead of SCC crack tips

Crack tips prepared from Ni-based alloys after stress corrosion cracking testing in simulated pressurized water reactor primary water have been studied by high-resolution characterization. Diffusion-induced grain boundary migration (DIGM) was observed in all the cracks and its potential role on the crack propagation is discussed in detail. The extent of DIGM observed changed with grain boundary type and alloy composition, which could lead to different extent of retardation effects on the crack propagation. A method is proposed to quantify the role of DIGM on crack propagation based on the results obtained in this work