Protecting p53 from degradation

Inactivation of the p53 function is a common event in cancer. Approx. 50% of human tumours express mutant p53 and there is evidence that in others, including many childhood tumours, p53 function is impaired in other ways. These defects on p53 function may be due to the alteration of cellular factors that modulate p53 or to the expression of viral oncoproteins. Radiotherapy and many of the chemotherapeutic drugs currently used in cancer treatment are potent activators of p53. However, most of these therapies have a serious drawback; that is, the long-term consequences of their DNA-damaging effects. Understanding the mechanisms regulating p53 stability is crucial for the development of new strategies to activate p53 non-genotoxically. Here we describe the effect of a potent activator of the p53 response, the nuclear export inhibitor leptomycin B, on Mdm2 degradation and we provide evidence for the oligomerization of the p14ARF tumour suppressor and Mdm2 inhibitor in response to oxidative stress.     

Targeted cytotoxic effect of anti-JL1 immunotoxin against a human leukemic cell line and its clinical implications

We have previously reported the identification of a unique thymocyte-specific surface molecule, JL1, which was detected using the monoclonal antibody (mAb), anti-JL1. Interestingly, JL1 was shown to be expressed in most leukemias, irrespective of their immunophenotype, and subpopulations of normal bone marrow (BM) mononuclear cells (MNCs). Here we investigated the potential usefulness of the anti-JL1 mAb as a therapeutic tool for leukemia. We demonstrated that the proliferation of cultured human leukemia cells was dramatically inhibited in vitro by anti-JL1 mAb conjugated with the polypeptide toxin, gelonin, but not by gelonin alone. We then systematically investigated the reactivity of the anti-JL1 mAb against normal human tissues to evaluate possible side effects along with various hematopoietic and nonhematopoietic tumor cell lines. All of 33 types of normal tissues except thymus and subpopulation of BM MNCs were clearly devoid of JL1 expression. Among tumor cell lines, all the nonhematopoietic cell lines tested were negative for JL1 expression, while some hematopoietic cell lines contained JL1 antigen. Collectively, the results showed the cytotoxic effects of anti-JL1-based immunotoxin against JL1-positive leukemic cells, sparing most normal tissues other than thymocytes and some BM MNCs. Therefore, we strongly suggest that gelonin-conjugated anti-JL1 mAb immunotoxin could be developed as a potential immunotherapeutic agent in the treatment of various types of JL1-positive acute leukemias.     

Cytomegalovirus-mediated upregulation of chemokine expression correlates with the acceleration of chronic rejection in rat heart transplants

Cytomegalovirus (CMV) infections have been shown to dramatically affect solid organ transplant graft survival in both human and animal models. Recently, it was demonstrated that rat CMV (RCMV) infection accelerates the development of transplant vascular sclerosis (TVS) in both rat heart and small bowel graft transplants. However, the mechanisms involved in this process are still unclear. In the present study, we determined the kinetics of RCMV-accelerated TVS in a rat heart transplant model. Acute RCMV infection enhances the development of TVS in rat heart allografts, and this process is initiated between 21 and 24 days posttransplantation. The virus is consistently detected in the heart grafts from day 7 until day 35 posttransplantation but is rarely found at the time of graft rejection (day 45 posttransplantation). Grafts from RCMV-infected recipients had upregulation of chemokine expression compared to uninfected controls, and the timing of this increased expression paralleled that of RCMV-accelerated neointimal formation. In addition, graft vessels from RCMV-infected grafts demonstrate the increased infiltration of T cells and macrophages during periods of highest chemokine expression. These results suggest that CMV-induced acceleration of TVS involves the increased graft vascular infiltration of inflammatory cells through enhanced chemokine expression.     

Clearance of a productive lentivirus infection in calves experimentally inoculated with caprine arthritis-encephalitis virus

Lentiviruses have long been considered host-specific pathogens, but several recent observations demonstrated their capacity to conquer new hosts from different species, genera, and families. From these cross-species infections emerged new animal and human infectious diseases. The successful colonization and adaptation of a lentivirus to a nonnatural host depends on unspecific and specific host barriers. Some of those barriers exert a relative control of viral replication (i.e., cytotoxic T-lymphocyte response, viral inhibitory factors), but none of them was found able to totally clear the infection once the retrovirus is fully adapted in its host. In this study we examined the evolution of the host-lentivirus interactions occurring in an experimental animal model of cross-species infection in order to analyze the efficiency of those barriers in preventing the establishment of a persistent infection. Five newborn calves were inoculated with caprine arthritis-encephalitis virus (CAEV), and the evolution of infection was studied for more than 12 months. All the animals seroconverted in the first 0.75 to 1 month following the inoculation and remained seropositive for the remaining time of the experiment. Viral infection was productive during 4 months with isolation of replication competent virus from the blood cells and organs of the early euthanized animals. After 4 months of infection, neither replication-competent virus nor virus genome could be detected in blood cells or in the classical target organs, even after an experimental immunosuppression. No evidence of in vitro restriction of CAEV replication was observed in cells from tissues explanted from organs of these calves. These data provide the demonstration of a natural clearance of lentivirus infection following experimental inoculation of a nonnatural host, enabling perspectives of development of new potential vaccine strategies to fight against lentivirus infections.     

An alternative technique to reveal polysaccharides in Toxoplasma gondii tissue cysts

Ultrathin sections of tissue cysts isolated from the brain of Toxoplasma gondii infected mice were submitted to two different methodologies derived from the periodic acid - Schiff's reagent (PAS) technique. The use of osmium tetroxide vapor as a developing agent of the aldehyde oxidation to reveal polysaccharides with periodic acid resulted in positive reaction in amylopectin granules in bradyzoites, as well as in the wall and matrix of the cysts, with excellent increment of the ultrastructural morphology. This technique can be used for study of T. gondii-host cell intracellular cycle, the differentiation tachyzoite-bradyzoite, and also for the formation of cysts into the host cells.     

Computer analysis of regulating metabolism of glycerol-3-phosphate in proteobacteria genome

Comparative computer-assisted analysis was used to study putative GlpR-regulons responsible for metabolism of glycerol and glycerol-3-phosphate in genomes of alpha-, beta-, and gamma-proteobacteria. New palindromic GlpR-binding signals were identified in gamma-proteobacteria; consensus sequences being TGTTCGATAACGAACA for Enterobacteriaceae, wTTTTCGTATACGAAAAw for Pseudomonadaceae, and AATGCTCGATCGAGCATT for Vibrionaceae. The signals in alpha- and beta-proteobacteria were also identified: they contained 3-4 direct TTTCGTT repeats separated by 3-4 nucleotide pairs.     

Estrogen regulates cytokine production and apoptosis in PMA-differentiated,macrophage-like U937 cells

We have investigated the effects of sex steroids, estradiol (E2), and testosterone (T) on the synthesis of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) in phorbol-myristate-acetate (PMA)-differentiated human monoblastic U937 cells. The ability of both hormones to modulate the viability and programmed cell death of macrophage-like PMA-differentiated U937 cells was also inspected. E2 increased TNF-alpha synthesis, whereas T had no effect on the production of this cytokine. The combination of E2 and its antagonist tamoxifen or ICI-182,789 completely abolished the induction of TNF-alpha, while combination of T and its antagonist Casodex (CSDX) did not significantly affect TNF-alpha production by U937 cells. Exposure of cells to E2 resulted in a dose-dependent decrease of IL-10 synthesis, while again T did not show any detectable effect. In addition, E2 induced a significant increase of apoptosis in macrophage-like U937 cells and this increase was inhibited by the simultaneous addition of either tamoxifen or ICI-182. In contrast, T alone or in combination with CSDX did not modify apoptotic rates of U937 cells. This evidence, taken together, suggests that estrogens, but not androgens, exert a pro-inflammatory action through the modulation of TNF-alpha and IL-10, and regulate the immune effector cells by the induction of programmed cell death.     

Polyglutamines placed into context

Nine inherited neurodegenerative disorders result from polyglutamine expansions. Two recently published papers on spinocerebellar ataxia type 1, together with studies on spinobulbar muscular atrophy last year, indicate that host protein context is the key arbiter of polyglutamine disease protein toxicity. This insight may represent the most important development in the field since the recognition of nuclear inclusions or the propensity of polyglutamine to aggregate. Indeed, an intimate and inextricable relationship may exist between polyglutamine neurotoxicity and the normal interactions, domains, modifications, and functions of the respective disease proteins.     

Identification and characterization of a Cryptococcus neoformans ATP binding cassette (ABC) transporter-encoding gene,CnAFR1, involved in the resistance to fluconazole

Resistance to fluconazole is a possible event during prolonged suppressive drug therapy for cryptococ-cal meningitis, the most frequently encountered life-threatening manifestation of cryptococcosis. The knowledge of this resistance at the molecular level is important for management of cryptococcosis. In order to identify genes involved in azole resistance in Cryptococcus neoformans, a cDNA subtraction library technique was chosen as a strategy. First, a fluconazole-resistant mutant BPY22.17 was obtained from a susceptible clinical isolate BPY22 by in vitro exposure to the drug. Then, a subtractive hybridization procedure was used to compare gene expression between the obtained strains. We identified a cDNA overexpressed in the fluconazole-resistant strain BPY22.17 that was used as a probe to isolate the entire gene in a C. neoformans genomic library. Sequence analysis of this gene identified an ATP Binding Cassette (ABC) transporter-encoding gene called C. neoformans AntiFungal Resistance 1 (CnAFR1). Disruption of CnAFR1 gene in the resistant isolate (BPY22.17) resulted in an enhanced susceptibility of the knock-out mutant cnafr1 against fluconazole, whereas reintroduction of the gene in cnafr1 resulted in restoration of the resistance phenotype, thus confirming that CnAFR1 is involved in fluconazole resistance of C. neoformans. Our findings therefore reveal that an active drug efflux mechanism can be involved in the development of azole resistance in this important human pathogen.     

Crystal structure of the YGR205w protein from Saccharomyces cerevisiae: close structural resemblance to E. coli pantothenate kinase

The protein product of the YGR205w gene of Saccharomyces cerevisiae was targeted as part of our yeast structural genomics project. YGR205w codes for a small (290 amino acids) protein with unknown structure and function. The only recognizable sequence feature is the presence of a Walker A motif (P loop) indicating a possible nucleotide binding/converting function. We determined the three-dimensional crystal structure of Se-methionine substituted protein using multiple anomalous diffraction. The structure revealed a well known mononucleotide fold and strong resemblance to the structure of small metabolite phosphorylating enzymes such as pantothenate and phosphoribulo kinase. Biochemical experiments show that YGR205w binds specifically ATP and, less tightly, ADP. The structure also revealed the presence of two bound sulphate ions, occupying opposite niches in a canyon that corresponds to the active site of the protein. One sulphate is bound to the P-loop in a position that corresponds to the position of beta-phosphate in mononucleotide protein ATP complex, suggesting the protein is indeed a kinase. The nature of the phosphate accepting substrate remains to be determined.