Identification and characterization of the frog virus 3 DNA methyltransferase gene

Cytosine DNA methyltransferases (MTases) first recognize specific nucleotide sequences and then transfer a methyl group from S-adenosylmethionine to cytosine. This division of function is reflected in five highly conserved motifs shared by cytosine MTases. The region containing the first four motifs is responsible for the catalytic function whereas the region containing the fifth motif V provides specificity of binding to DNA. In at least one case, two separate proteins, one containing the first four motifs and the second containing the last motif combine to provide full functional activity. In the frog virus 3 (FV3) genome we have identified an open reading frame (ORF) whose deduced amino acid (aa) sequence contains motifs characteristic of prokaryotic as well as eukaryotic MTases. The ORF consists of 642 bp which codes for a protein of 214 aa with a predicted molecular mass of 24.8 kDa. This ORF contains the first four highly conserved motifs of cytosine MTases but the fifth motif, responsible for DNA binding specificity, is missing. Presumably, FV3 MTase is composed of two subunits. Northern blot analysis showed that the putative MTase ORF is transcribed into two transcripts belonging to the delayed-early class of FV3 messages. These two transcripts appear to be initiated at two different start sites but terminate in the same 3' region of the gene. The transcription start sites are not preceded by any known promoter sequences, but two regions of hyphenated dyad symmetry are present at the 3' end of the message. A protein with a molecular mass of approximately 28 kDa was synthesized by a rabbit reticulocyte lysate programmed with capped runoff transcripts from the cloned gene, suggesting that the ORF can be transcribed into a message coding for a viral protein. Overall, our results suggest that we have identified a gene for a subunit of MTase in the FV3 genome.

A testicular protein important for fertility has glutathione S-transferase activity and is localized extracellularly in the seminiferous tubules

A 24-kDa protein isolated by preparative gel electrophoresis from rat testes was reported by us as an active immunogen in rats. Anti-24-kDa antibodies inhibited murine sperm-oocyte binding in vitro. Here, we show similarity at the NH2 terminus shared by this protein purified on Sephadex G-75 followed by anion exchange high performance liquid chromatography with glutathione S-transferase (GST)-mu subunits. This protein purified by glutathione affinity chromatography also demonstrated similarity to GST-mu NH2 terminus in a 30-amino-acid overlap. Both proteins showed activity toward the GST substrate 1-chloro-2,4-dinitrobenzene (Km of 33 microM and 50 microM) which was inhibited by 17 beta-estradiol 3-sulfate. Antisera against both proteins recognized liver GST-mu on Western blots and sperm acrosome of multiple species immunocytochemically. Both antisera significantly inhibited in vitro fertilization of goat oocytes by sperm preincubated with them while anti-liver GST sera did not. GST activity was localized on rat sperm, seminiferous tubular fluid, and Sertoli cells. Seminiferous tubular fluid 24-kDa protein shared similarity to the NH2 terminus of GST-mu subunits in a 20-amino-acid overlap. Time-dependent accumulation of GST was detected in the spent culture medium of seminiferous tubules from rats of different ages suggesting secretion.

Acute starvation decreases acetylcholinesterase activity in different regions of rat brain

The activity of acetylcholinesterase (AChE) was assayed spectrophotometrically in four brain regions of rats that had been deprived of food for 96 h. A significant decrease in the total AChE activity (by 4-45%) as well as in its specific activity (by 14-28%) was observed in the supernatant and total particulate fractions from cerebral hemispheres, cerebellum, brainstem and diencephalon + basal ganglia. Similarly, blood glucose, body weight and protein content of subcellular fractions from most brain regions showed decreases after starvation.

Protein kinase C associates with intermediate filaments and stress fibers

The subcellular distribution of protein kinase C (PKC) was determined by immunofluorescence using anti-PKC monoclonal antibodies (MAbs). The antibodies used were: (1) 1.9 MAb that is directed against an epitope in the catalytic domain of PKC, (2) 1.3 MAb that recognizes an isozyme of PKC (Mochly-Rosen, D., and Koshland, D. E., 1987, J. Biol. Chem. 262, 2291-2297; Mochly-Rosen, D., et al. 1987 Proc. Natl. Acad. Sci. USA 84, 4660-4664) and (3) MC-2a MAb that is directed against the beta-isozyme of PKC (Usuda, N., et al. 1991, J. Cell Biol. 112, 1241-1247). The cells used in this study were baby hamster kidney cells, vimentin+ and vimentin- clones of SW13 (a human adrenal carcinoma cell line), CEM (a human T cell line), U937 (a histiocytic myeloid cell line), and HL60 (a promyelocytic leukemia cell line). The 1.9 MAb was found to recognize a variety of subcellular components, viz., nucleus (nucleoplasm and nucleolus), cytoplasm, vimentin-type intermediate filaments (IF), stress fibers, and cell membrane. Among these components the beta-isozyme-specific MAbs (1.3 and MC-2a) recognized only the IF network, stress fibers, and edges of the cell membrane. Experiments with vimentin+ and vimentin- mutants of SW13 cells, double indirect immunofluorescence studies with anti-vimentin and anti-PKC antibodies, and drug studies confirmed that the IF network is the predominant cytoskeletal network labeled with all anti-PKC MAbs. Immunoblotting studies with the MC-2a MAb revealed that the observed staining of the IF network was not due to a cross-reaction of the MAb with IF proteins and that the MAb specifically recognizes PKC. These studies, while identifying the diverse cell components to which PKC binds, have demonstrated, for the first time, that PKC associates with the IF network in a variety of cell types. Additionally, the studies have confirmed the studies by others concerning the association of PKC with stress fibers.

Secondary immune defects in non-Hodgkin's lymphoma

Changes in the humoral, cellular and phagocytic components of the immune system were investigated in 44 biopsy proven, untreated patients of non-Hodgkin's lymphoma (NHL). There was significant decrease in the total lymphocyte number, their subsets (T and B) and the T helper (T mu) population. Impaired leukocyte migration inhibition response and DNA synthesis following stimulation by phytohaemagglutinin were noted. Significant reduction of serum IgA was found in patients of both diffuse and nodular NHL. Phagocytic activity and nitroblue tetrazolium (NBT) reduction were unaltered, but chemotaxis was significantly reduced and bactericidal activity showed variable results.

Secretion of single-chain urokinase-type plasminogen activator from insect cells

A cDNA encoding human urokinase-type plasminogen activator was inserted downstream from the polyhedrin promoter of the baculovirus Autographa californica nuclear polyhedrosis virus. A protein of similar Mr to urokinase (UK) was synthesized and approx. 90% was secreted from recombinant virus-infected Spodoptera frugiperda cells. Zymography and Western blotting analysis of the insect-derived protein demonstrated that it was comprised solely of the high-Mr form of UK. No low-Mr UK was detected. Amidolytic activity assays showed that 96% of the insect cell-derived UK was in the single-chain proenzyme form. The yield of UK from insect cells was 1986 international units/ml/10(6) infected cells.

Effect of acute starvation on monoamine oxidase and Na+,K(+)-ATPase activity in rat brain

The activities of monoamine oxidase (MAO), responsible for oxidative deamination of many biogenic amines, and Na+, K(+)-ATPase, which plays a crucial role in the release mechanism of neurotransmitters, were determined in rat brain after acute starvation. They were assayed biochemically from four different regions of the brain in two subcellular fractions. Acute starvation decreased the activity of MAO, whereas the Na+,K(+)-ATPase activity was increased. An effect of starvation was also seen on the blood glucose level, body wt, and the protein content of different brain regions. Starvation or normal dietary fluctuations of certain nutrients that exert precursor influence over neurotransmitter synthesis are important to the brain, and contribute to its regulation of both neuroendocrine response and behavior. A rise in the substrate level, i.e., ATP, as a result of increased utilization of ketone bodies and low level of monoamines in the brain after acute starvation, may be the underlying factor for increasing the activity of Na+,K(+)-ATPase in rat brain. These results suggest that, probably, certain adaptive mechanisms become operative in the brain under disturbed physiological conditions.

Parovarian cystadenocarcinoma: a case report

Although primary ovarian carcinomas are frequent, carcinomas having a primary origin in parovarian cysts are extremely rare. The majority of neoplasms developing in parovarian cysts are benign serous tumours. Only 9 cases of parovarian adenocarcinoma have been reported so far in the world literature. Out of these 6 have been of low grade malignancy. Of the rest 3 cases also, only one was invasive. The case described here appears to be the second case of parovarian adenocarcinoma which was invasive. The origin of this tumour is discussed together with a brief review of literature on adenocarcinomas of parovarian origin.

Carboxyhaemoglobin and serum cholesterol levels in smokers

Carboxyhaemoglobin (COHb) and serum cholesterol levels were studied in twenty five chronic smokers, smoking different quantities of cigarettes, biris and "hooka" for more than ten years and compared with equal number of age and sex matched non-smoker controls. COHb levels were found to be significantly higher (P less than 0.001) in chronic smokers as compared to non-smokers while no significant difference (P greater than 0.1) was found in serum cholesterol levels between the two groups. Cigarette smokers had a higher COHb level as compared to biris smokers (P less than 0.001).

Methotrexate-resistant Leishmania donovani genetically deficient in the folate-methotrexate transporter

From a mutagenized population of wild type Leishmania donovani promastigotes, a clone was isolated in a single step by virtue of its resistance to 1 mM methotrexate, a potent inhibitor of dihydrofolate reductase. This methotrexate-selected cell line, MTXA5, was cross-resistant to aminopterin but just as sensitive to growth inhibition caused by pyrimethamine, trimethoprim, and cytotoxic purine and pyrimidine analogs. Unlike previously characterized methotrexate-resistant Leishmania (Coderre, J. A., Beverley, S. M., Schimke, R., and Santi, D. V. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 2132-2136), resistance to the antimetabolite was not due to gene amplification or increased dihydrofolate reductase activity. The genetic defect in MTXA5 cells appeared to be in the methotrexate-folate transport system. The rate of uptake and transport of [3H]methotrexate and [3H]folate into MTXA5 cells was less than 1% of that of wild type parental cells. Neither wild type nor MTXA5 cells could multiply in folate-deficient medium, and thymine and thymidine at concentrations which circumvented methotrexate toxicity, did not restore the ability of Leishmania to grow. The concentration of exogenous folate that restored growth of wild type and mutant cells, however, was virtually identical, although MTXA5 cells, unlike parental cells, could not proliferate in folate-deficient medium supplemented with 10 microM biopterin. Interestingly, methotrexate and aminopterin could stimulate the growth of both leishmanial strains in folate-deficient medium, suggesting that these antifolate analogs were serving as a pteridine source for the parasite. These somatic cell genetic studies of folate transport in Leishmania provide genetic evidence for a specific folate permease in L. donovani promastigotes and have important implications concerning the mechanisms by which these parasites utilize exogenous pteridines and folates and by which they might become resistant to parasite-directed chemotherapeutic regimens.

Two high affinity nucleoside transporters in Leishmania donovani

A rapid sampling kinetic technique has been used to evaluate the nucleoside transport functions of Leishmania donovani. The results indicated that L. donovani promastigotes possessed two independent purine nucleoside transporters with nonoverlapping substrate specificity. The first transported inosine, guanosine, and their analogs, while the second carried adenosine, analogs of adenosine, and the pyrimidine nucleosides, uridine, cytidine, and thymidine. The apparent Km values of the two nucleoside permeases for their purine nucleoside substrates were extraordinarily low, in the micromolar range. The organisms were capable of concentrating purine nucleosides from the medium and converting them to the nucleotide level with great efficiency and rapidity. Inosine and adenosine transport could be distinguished by different sensitivities to sulfhydryl reagents, suggesting structural differences between the two transporters. Finally, the two nucleoside transport systems of L. donovani were virtually refractory to inhibition by 4-nitrobenzylthioinosine and dipyridamole, two potent inhibitors of nucleoside entry into mammalian cells.

Effects of DL-alpha-difluoromethylornithine on Leishmania donovani promastigotes

Alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, has been demonstrated to be an effective agent against a variety of parasitic protozoa but not against Leishmania spp. In this report, we show that Leishmania donovani promastigotes in continuous culture are sensitive to the growth inhibitory and cytotoxic effects of DFMO. Incubation of the promastigotes with DFMO obliterates intracellular putrescine pools and depletes spermidine concentrations, which correlates with the onset of growth inhibition. The effects of DFMO on the growth and the intracellular polyamine pools can be reversed completely by the addition of 10 microM putrescine to the culture medium. These results suggest that the treatment of leishmaniasis may be amenable to chemotherapeutic manipulation by DFMO.

Adenine phosphoribosyltransferase-deficient Leishmania donovani

Mutant promastigotes of Leishmania donovani deficient in adenine phosphoribosyltransferase (APRTase) have been isolated in medium containing 4-aminopyrazolopyrimidine. The generation of APRTase-deficient mutants occurred in two discrete steps. In the first step, clones were isolated with 50% of wildtype levels of APRTase activity. These cells were reselected and colonies totally deficient in APRTase were isolated. Partially and totally APRTase-deficient cells exhibited intermediate and complete resistance to cytotoxic adenine analogs, respectively. Nevertheless, wildtype and mutant cells could salvage adenine and utilize adenine as a purine source equally efficiently, suggesting that the adenine deaminase-HGPRTase pathway plays an important role in promastigote adenine metabolism. Kinetic and thermal inactivation studies of purified APRTase and isoelectric focusing of crude extracts from wildtype and partially APRTase-deficient cells suggested that the latter cells possessed wildtype APRTase activity at half the amount found in wildtype parental cells. These data suggest that Leishmania donovani possess two copies of the APRTase structural gene and that these organisms might be diploid for the APRTase locus.

Genetic analysis of adenine metabolism in Leishmania donovani promastigotes. Evidence for diploidy at the adenine phosphoribosyltransferase locus

Mutant promastigotes of Leishmania donovani deficient in adenine phosphoribosyltransferase (AP-Rib transferase) have been isolated in medium containing 4-aminopyrazolopyrimidine. The generation of AP-Rib transferase-deficient mutants occurred in two discrete steps. In the first step, clones were isolated with 50% of wild-type levels of AP-Rib transferase activity. These cells were reselected, and colonies totally deficient in AP-Rib transferase were isolated. Wild-type and AP-Rib transferase-deficient cells contained equivalent amounts of other enzymes essential to adenine metabolism such as adenine deaminase and hypoxanthine-guanine phosphoribosyltransferase. Partially and totally AP-Rib transferase-deficient cells exhibited intermediate and complete resistance to cytotoxic adenine analogs, respectively. Nevertheless, wild-type and mutant cells could salvage adenine and utilize adenine as a purine source equally efficiently, suggesting that the adenine deaminase-hypoxanthine-guanine phosphoribosyl-transferase pathway plays an important role in promastigote adenine metabolism. Kinetic and thermal inactivation studies of purified AP-Rib transferase and isoelectric focusing of crude extracts from wild-type and partially AP-Rib transferase-deficient cells suggested that the latter cells possessed wild-type AP-Rib transferase activity at half the amount found in wild-type parental cells. These data suggest that L. donovani possesses two copies of the AP-Rib transferase structural gene and that these organisms might be diploid for the AP-Rib transferase locus.

Biochemical genetic analysis of formycin B action in Leishmania donovani

Formycin B is cytotoxic toward Leishmania and is a potential chemotherapeutic agent for leishmaniasis. In order to determine the mechanism of action of formycin B, we have isolated and characterized clonal populations of formycin B-resistant Leishmania donovani. These formycin B-resistant clones are also cross-resistant to formycin A and allopurinol riboside-mediated growth inhibition. Incubation of the formycin B-resistant cells with [3H]formycin B indicates that, unlike wild type cells, the resistant populations cannot accumulate phosphorylated metabolites of exogenous [3H]formycin B. This is due to a defective transport system for formycin B in the resistant cells. However, wild type and mutant cells incorporate [3H]formycin A equally efficiently into [3H]formycin A-containing nucleotides and into RNA. These data suggest that formycin B cytotoxicity in Leishmania is not mediated by its incorporation as the adenosine analog into RNA. A plausible alternative hypothesis is proposed for the mechanism of action of the pyrazolo (4,3-d)pyrimidine C-nucleosides based upon depletion of an essential intracellular metabolite.