The role of copper in drug-resistant murine and human tumors

Multidrug resistance (MDR) is still a major threat to successful clinical application of cancer chemotherapy. Copper plays an important role in biological systems, and copper is also involved in carcinogenesis. In the present investigation, we addressed the question whether metal copper might be involved in drug resistance of murine and human tumors. By means of atomic absorption spectroscopy, we determined serum copper concentrations. We found that the blood serum of tumor-bearing mice contained higher amounts of copper than healthy mice with tumors. Secondly, mice bearing doxorubicin-resistant Ehrlich ascites carcinoma- or cyclophosphamide-resistant Lewis lung carcinoma contained more copper in their serum than mice bearing the corresponding drug-sensitive parental tumors. Furthermore, the analysis of patients with breast cancer, colon carcinoma or lung cancer showed that the serum copper contents were higher in patients not responding to chemotherapy when compared to patients whose tumors responded to treatment. The copper levels in serum of healthy volunteers were lower than in cancer patients irrespective of their response to chemotherapy. Our results imply that the level of serum copper may be considered as a biomarker for treatment response.     

Insight into the salt tolerance factors of a wild halophytic rice, <Emphasis Type="Italic">Porteresia coarctata</Emphasis>: a physiological and proteomic approach

Salinity poses a serious threat to yield performance of cultivated rice in South Asian countries. To understand the mechanism of salt-tolerance of the wild halophytic rice, Porteresia coarctata in contrast to the salt-sensitive domesticated rice Oryza sativa, we have compared P. coarctata with the domesticated O. sativa rice varieties under salinity stress with respect to several physiological parameters and changes in leaf protein expression. P. coarctata showed a better growth performance and biomass under salinity stress. Relative water content was conserved in Porteresia during stress and sodium ion accumulation in leaves was comparatively lesser. Scanning electron microscopy revealed presence of two types of salt hairs on two leaf surfaces, each showing a different behaviour under stress. High salt stress for prolonged period also revealed accumulation of extruded NaCl crystals on leaf surface. Changes induced in leaf proteins were studied by two-dimensional gel electrophoresis and subsequent quantitative image analysis. Out of more than 700 protein spots reproducibly detected and analyzed, 60% spots showed significant changes under salinity. Many proteins showed steady patterns of up- or downregulation in response to salinity stress. Twenty protein spots were analyzed by MALDI-TOF, leading to identification of 16 proteins involved in osmolyte synthesis, photosystem functioning, RubisCO activation, cell wall synthesis and chaperone functions. We hypothesize that some of these proteins confer a physiological advantage on Porteresia under salinity, and suggest a pattern of salt tolerance strategies operative in salt-marsh grasses. In addition, such proteins may turn out to be potential targets for recombinant cloning and introgression in salt-sensitive plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pulsed low-energy stimulation initiates electric turbulence in cardiac tissue

Interruptions in nonlinear wave propagation, commonly referred to as wave breaks, are typical of many complex excitable systems. In the heart they lead to lethal rhythm disorders, the so-called arrhythmias, which are one of the main causes of sudden death in the industrialized world. Progress in the treatment and therapy of cardiac arrhythmias requires a detailed understanding of the triggers and dynamics of these wave breaks. In particular, two very important questions are: 1) What determines the potential of a wave break to initiate re-entry? and 2) How do these breaks evolve such that the system is able to maintain spatiotemporally chaotic electrical activity? Here we approach these questions numerically using optogenetics in an in silico model of human atrial tissue that has undergone chronic atrial fibrillation (cAF) remodelling. In the lesser studied sub-threshold illumination régime, we discover a new mechanism of wave break initiation in cardiac tissue that occurs for gentle slopes of the restitution characteristics. This mechanism involves the creation of conduction blocks through a combination of wavefront-waveback interaction, reshaping of the wave profile and heterogeneous recovery from the excitation of the spatially extended medium, leading to the creation of re-excitable windows for sustained re-entry. This finding is an important contribution to cardiac arrhythmia research as it identifies scenarios in which low-energy perturbations to cardiac rhythm can be potentially life-threatening.     

Genetic Dissection of Epistatic Interactions Contributing Grain Yield Variability in Rice under Drought

AimsThe aim of the present study was to evaluate the performance of ‘high’-‘low’ yielding pyramided lines (PLs), having the same combinations of qDTYs in Samba Mahsuri, MR219 and IR64-Sub1 genetic backgrounds, and to understand the genetic interactions among QTL and/with genetic background affecting grain yield.BackgroundEpistasis regulates the expression of traits governed by several major/minor genes/QTL. Multiple pyramided lines (PLs) with the same grain yield QTL (qDTYs) combinations but possessing grain yield variability under different levels of reproductive stage drought stress were identified in different rice genetic backgrounds at International Rice Research Institute (IRRI).ObjectivesThe objectives of the present study were to evaluate the performance pyramided lines (PLs) with drought QTL in the backgrounds of Samba Mahsuri, MR219 and IR64-Sub1 under reproductive stage drought stress (RS) and NS (non-stress) conditions, to understand the effect of epistatic interactions among qDTYs and with genetic background on GY under the differential level of stress and to identify the promising drought-tolerant lines with high yield under drought and higher background recovery in different genetic backgrounds.MethodsThe experiments were conducted in 2015 DS (dry season), 2015 WS (wet season) and 2017 DS at IRRI, Los Baños, Philippines, in a transplanted lowland ecosystem under lowland severe stress (LSS), lowland moderate stress (LMS) and lowland non-stress (LNS). The experiments were laid out in alpha lattice design with two replications.ResultsSeveral digenic interactions were found in different genetic backgrounds, 13 interactions in Samba Mahsuri, 11 in MR219 and 20 in IR64-Sub1 backgrounds. Among all digenic interactions, one QTL × QTL interaction, 17 QTL × background and 26 background × background interactions resulted in GY reduction in low yielding PLs in different genetic backgrounds under LSS or LMS. Negative interaction of qDTY_3.1, qDTY_4.1 and qDTY_9.1 with background markers and background × background interactions caused up to 15% GY reduction compared to the high yielding PLs under LMS in the Samba Mahsuri PLs. In MR219 PLs, the negative interaction of qDTY_2.2, qDTY_3.2, qDTY_4.1 and qDTY_12.1 with the background marker interval RM314-RM539, RM273-RM349 and RM445-RM346, RM473D-RM16, respectively resulted 52% GY reduction compared to the high yielding PLs under LSS. In IR64-Sub1 PLs, qDTY_6.1 interacted with background loci at RM16-RM135, RM228-RM333, RM202-RM287 and RM415-RM558A marker interval under LSS and at RM475-RM525 marker interval under LMS, causing GY reduction to 58% compared to the high yielding PLs.ConclusionHigh yielding PLs in Samba Mahsuri (IR 99734:1-33-69-1-22-6), MR219 (IR 99784-156-87-2-4-1) and IR64-Sub1 (IR 102784:2-89-632-2-1-2) backgrounds without any negative interactions were identified. The identified selected promising PLs may be used as potential drought-tolerant donors or may be released as varieties for drought-prone ecosystems in different countries.     

Topological analyses of the L-lysine exporter LysO reveal a critical role for a conserved pair of intramembrane solvent-exposed acidic residues

LysO, a prototypical member of the LysO family, mediates export of L-lysine (Lys) and resistance to the toxic Lys antimetabolite, L-thialysine (Thl) in Escherichia coli. Here, we have addressed unknown aspects of LysO function pertaining to its membrane topology and the mechanism by which it mediates Lys/Thl export. Using substituted cysteine (Cys) accessibility, here we delineated the membrane topology of LysO. Our studies support a model in which both the N- and C-termini of LysO are present at the periplasmic face of the membrane with a transmembrane (TM) domain comprising eight TM segments (TMSs) between them. In addition, a feature of intramembrane solvent exposure in LysO is inferred with the identification of membrane-located solvent-exposed Cys residues. Isosteric substitutions of a pair of conserved acidic residues, one E233, located in the solvent-exposed TMS7 and the other D261, in a solvent-exposed intramembrane segment located between TMS7 and TMS8, abolished LysO function in vivo. Thl, but not Lys, elicited proton release in inside-out membrane vesicles, a process requiring the presence of both E233 and D261. We postulate that Thl may be exported in antiport with H⁺ and that Lys may be a low-affinity export substrate. Our findings are compatible with a physiological scenario wherein in vivo LysO exports the naturally occurring antimetabolite Thl with higher affinity over the essential cellular metabolite Lys, thus affording protection from Thl toxicity and limiting wasteful export of Lys.     

Mode of action of pentavalent antimonials: specific inhibition of type I DNA topoisomerase of Leishmania donovani

Sodium stibogluconate and Ureastibamine, two potent antileishmanial drugs specifically inhibit the relaxation of supercoiled plasmid pBR322 catalyzed by DNA topoisomerase I of Leishmania donovani. Dose dependent inhibition suggests that the drugs interact with the enzyme rather than the DNA. The inhibition reported here concerning a type I DNA topoisomerase demonstrates at least one possible mode of action of these antileishmanial drugs.     

Purification and characterization of a motility initiating protein from caprine epididymal plasma

Numerous reports have appeared on the occurrence of undefined protein factors in male reproductive fluids that promote motility of mature sperm and initiate forward motility in the immature (immotile) caput‐epididymal sperm. This study reports for the first time purification to apparent homogeneity of a motility initiating protein (MIP) from epididymal plasma and its characterization using the caprine sperm model. It is a 125 kDa (approximately) dimeric protein made up of two subunits: 70 and 54 kDa. MIP is an acidic protein with an isoelectric point of 4.75. The motility protein at 30 µg/ml (240 nM) level showed nearly maximal motility‐promoting activity. MIP is heat stable and it is maximally active at pH 8. It is a glycoprotein that binds with high affinity to concanavalin A and it contains mannose, galactose, and N‐acetyl glucosamine approximately in the ratios of 6:1:6. It is sensitive to the actions of α‐mannosidase and β‐N‐acetylglucoseaminidase thereby demonstrating that the sugar side chain of the glycoprotein is essential for its biological activity. Epididymal plasma is its richest source. It is also capable of enhancing forward motility of mature cauda‐sperm. Its antibody markedly inhibits sperm motility. MIP antibody is highly immunospecific and it recognizes both the subunits. MIP causes significant increase of the intrasperm level of cyclic AMP. MIP: the physiological motility‐activating protein has potential for use as a contraceptive vaccine and for solving some of the problems of human infertility and animal breeding. J. Cell. Physiol. 222:254–263, 2010. © 2009 Wiley‐Liss, Inc.