A novel calcineurin-independent activity of cyclosporin A in Saccharomyces cerevisiae

Fungi rely on regulatory networks to coordinate sensing of environmental stress with initiation of responses crucial for survival. Antifungal drugs are a specific type of environmental stress with broad clinical relevance. Small molecules with antifungal activity are ubiquitous in the environment, and are produced by a myriad of microbes in competitive natural communities. The echinocandins are fungal fermentation products and the most recently developed class of antifungals, with those in clinical use being semisynthetic derivatives that target the fungal cell wall by inhibiting 1,3-β-D-glucan synthase. Recent studies implicate the protein phosphatase calcineurin as a key regulator of cellular stress responses required for fungal survival of echinocandin-induced cell wall stress. Pharmacological inhibition of calcineurin can be achieved using the natural product and immunosuppressive drug cyclosporin A, which inhibits calcineurin by binding to the immunophilin Cpr1. This drug-protein complex inhibits the interaction between the regulatory and catalytic subunits of calcineurin, an interaction necessary for calcineurin function. Here, we report on potent activity of cyclosporin A when combined with the echinocandin micafungin against the model yeast Saccharomyces cerevisiae that is independent of its known mechanism of action of calcineurin inhibition. This calcineurin-independent synergy does not involve any of the 12 immunophilins known in yeast, individually or in combination, and is not mediated by any of the multidrug transporters encoded or controlled by YOR1, SNQ2, PDR5, PDR10, PDR11, YCF1, PDR15, ADP1, VMR1, NFT1, BPT1, YBT1, YNR070w, YOL075c, AUS1, PDR12, PDR1 and/or PDR3. Genome-wide haploinsufficiency profiling (HIP) and homozygous deletion profiling (HOP) strongly implicate the cell wall biosynthesis and integrity pathways as being central to the calcineurin-independent activity of cyclosporin A. Thus, systems level chemical genomic approaches implicate key cellular pathways in a novel mechanism of antifungal drug synergy.     

Expression of CD13/aminopeptidase N in precursor B-cell leukemia: role in growth regulation of B cells

Expression of cell surface CD13 in acute B-cell leukemia (ALL-B) is often viewed, as an aberrant expression of a myeloid lineage marker. Here, we attempted to study the stage specific expression of CD13 on ALL-B blasts and understand its role in leukemogenesis as pertaining to stage of B-cell ontogeny. A total of 355 cases of different hematological malignancies were diagnosed by immunophenotyping. Among 68 cases of early B-cell ALL, 22 cases with distinct immunophenotype was identified as immature B-cell ALL. Blasts from these ALL-B patients demonstrated prominent expression of CD10, CD19, CD22, but neither cytoplasmic nor surface IgM receptors. This strongly indicates leukemogenesis at an early stage of B-cell development. We also identified, the existence of a subpopulation of cells with remarkably similar phenotype in non-leukemic marrow from healthy subjects (expressing CD10, CD19, CD22, CD24, Tdt together with the co-expression of CD13). This sub-population of B cells concomitantly expressing CD13 appeared to be a highly proliferating group. By blocking their cell surface CD13 in leukemic blasts with monoclonal antibody we were able to inhibit their proliferation. We hypothesized that neoplastic transformation at this stage may be facilitated by CD13. CD13 may thus be an important target for novel molecular therapy of early stage acute B-cell leukemia.     

Short Communication: Photoinduced sporulation in Trichoderma harzianum–an experimental approach to primary events

Photoinduced sporulation in Trichoderma harzianum could be achieved in the dark in the presence of hydrogen peroxide. However, methylene blue could induce sporulation in red light. Acetylcholine in the presence of eserine when supplied exogenously could mimic blue light effects in complete darkness. Immediate changes in external pH after acetylcholine/eserine treatment were found to be the same as in the blue light induction.     

The role of serotonin and melatonin in plant morphogenesis: Regulation of auxin-induced root organogenesis in in vitro-cultured explants of st. John's Wort (Hypericum perforatum L.)

Summary St. John's wort (Hypericum perforatum cv. Anthos) is a medicinal plant with historical and anecdotal evidence of efficacy as an anti-depressant. Recent research has demonstrated an active biosynthetic pathway leading to the production of the mammalian neurohormone melatonin in St. John's wort plantlets. The objective of the current study was to assess the physiological role of melatonin and related indoleamines in plant morphogenesis. In the initial experiments, two of the indoleamines; serotonin and melatonin, were supplemented to the culture medium. In subsequent research, six inhibitors of auxin and indoleamine action or transport, 2,3,5-triiodobenzoic acid, p-chlorophenoxyisobutyric acid, p-chlorophenyl-alanine, d-amphetamine, fluoxetine (Prozac^TM), and methylphenidate (Ritalin^TM), were included in a culture medium in the presence or absence of the auxin, indoleacetic acid (IAA). The rate of de novo root and shoot organogenesis and the endogenous concentrations of auxin and indoleamines were determined in cultured explants. Significant reductions in de novo root regeneration were found to correspond with decreases in the pool of both IAA and melatonin. An increase in the endogenous concentration of melatonin was correlated with an increase in de novo root formation, and increased serotonin levels corresponded to increased shoot formation on the explants. Our findings provide the first evidence that a balance of the endogenous concentration of serotonin and melatonin may modulate plant morphogenesis in vitro.