Isolation and Molecular Identification of Microsporidian Pathogen Causing Nosemosis in Muga Silkworm, Antheraea assamensis Helfer (Lepidoptera: Saturniidae)

Microsporidia are intracellular fungal parasites and they are the most common pathogens for sericulture. Microsporidian sp. can cause pebrine, a dreadful disease and lead to destructive disorder in Muga silkworm, Antheraea assamensis Helfer by vertical and horizontal transmission. This disease is the key factor obstructing the developmental progress of Muga culture in India. Nevertheless, molecular identification and characterization of pathogen associated with pebrine disease in A. assamensis is not yet established. Insect bioassay studies revealed that microsporidian infection in Muga silkworm, A. assamensis Helfer significantly reduced (P < 0.005) cocoon weight, pupal weight, shell weight and silk ratios. A new set of PCR primers suitable for amplification of small subunit ribosomal RNA (SSU-rRNA) of microsporidia infecting A. assamensis have been designed. The amplicon was cloned, sequenced and analysed. Microsporidia pathogen of wild silk moth A. assamensis has been identified at genus level as Nosema sp. AA1. Phylogeny of Nosema sp. AA1 was constructed on the basis of SSU-rRNA sequence and it has a close evolutionary relationship with microsporidian pathogens of other wild silkmoths. The arrangement and organization of the rRNA genes inferred that Nosema sp. AA1 belongs to true Nosema group and not to members of the Nosema/Vairimorpha group.

Plumbagin inhibits proliferative and inflammatory responses of T cells independent of ROS generation but by modulating intracellular thiols

Plumbagin inhibited activation, proliferation, cytokine production, and graft-versus-host disease in lymphocytes and inhibited growth of tumor cells by suppressing nuclear factor-kappaB (NF-kappaB). Plumbagin was also shown to induce reactive oxygen species (ROS) generation in tumor cells via an unknown mechanism. Present report describes a novel role of cellular redox in modulation of immune responses in normal lymphocytes by plumbagin. Plumbagin depleted glutathione (GSH) levels that led to increase in ROS generation. The decrease in GSH levels was due to direct reaction of plumbagin with GSH as evinced by mass spectrometric and HPLC analysis. Further, addition of plumbagin to cells resulted in decrease in free thiol groups on proteins and increase in glutathionylation of proteins. The suppression of mitogen-induced T-cell proliferation and cytokine (IL-2/IL-4/IL-6/IFN-gamma) production by plumbagin was abrogated by thiol antioxidants but not by non-thiol antioxidants confirming that thiols but not ROS play an important role in biological activity of plumbagin. Plumbagin also abrogated mitogen-induced phosphorylation of ERK, IKK, and degradation of IkappaB-alpha. However, it did not affect phosphorylation of P38, JNK, and AKT. Our results for the first time show that antiproliferative effects of plumbagin are mediated by modulation of cellular redox. These results provide a rationale for application of thiol-depleting agents as anti-inflammatory drugs.

Enhanced sequential expression of G1/S cyclins during experimental epatocarcinogenesis and tyrosine phosphorylation

It is now widely accepted that cancer development is a multistage process, starting from the original cell population and ending with a malignant tumor. However, the mechanisms involved in the progressive growth of cells from normalcy to preneoplasia, and from preneoplasia to malignancy are not clear. Because tyrosine phosphorylation and dephosphorylation reactions are known to play critical roles during normal and abnormal cellular growth, we have studied the tyrosine phosphorylation, tyrosine phosphorylated proteins, and protein phosphatases during the sequential development of liver cancer. The present investigation indicated that enhanced tyrosine phosphorylation and tyrosine phosphorylated proteins, with no change in the levels of tyrosine protein phosphatases may contribute to abnormal cellular proliferation during liver carcinogenesis. We have also seen an increase in the expression of proliferating cell nuclear antigen and G1/S cyclins during tumor development.

Overexpression of G1/S cyclins and PCNA and their relationship to tyrosine phosphorylation and dephosphorylation during tumor promotion by metanil yellow and malachite green

Metanil yellow (MY) and Malachite green (MG) are textile dyes, which, despite the ban, occur unscrupulously as food colouring agents. Accordingly they constitute a serious public health hazard and are of sufficient environmental concern. We have earlier reported that both MY and MG have tumor promoting effects on the development of hepatic preneoplastic lesions induced by N-nitrosodiethylamine in rats. In order to understand the possible mechanism(s) by which metanil yellow (MY) and malachite green (MG) promotes liver tumor development, we have studied the tyrosine phosphorylation and protein phosphatases during tumor promotion. We have also investigated the possible overexpression of G1/S cyclins and PCNA during tumor promotion by MY and MG. The present investigation indicates that enhanced tyrosine phosphorylation is associated with no change in levels of tyrosine protein phosphatases. We have also observed an increase in the expression of PCNA and G1/S cyclins during tumor promotion. These factors collectively may contribute to the abnormal cell proliferation during tumor promotion by MY and MG.

Tyrosyl phosphorylation and activation of a type II phosphatidylinositol 4-kinase by p56(lck) in concanavalin A stimulated rat splenic lymphocytes

Recent evidence suggests that concanavalin A modulates tyrosyl phosphorylation and activation of a type II PtdIns 4-kinase in rat splenic lymphocytes. However, the regulatory protein tyrosine kinase(s) remain to be elusive. The present manuscript provides evidence that a type II PtdIns 4-kinase associates with p56(lck) in Con A stimulated rat splenic lymphocytes. In vitro phosphorylation studies suggest that p56(lck) regulates phosphorylation and activation of type II PtdIns 4-kinase. Inhibition of p56(lck) activity in vivo has shown to reduce tyrosyl phosphorylation and activation of PtdIns 4-kinase by Con A. These results suggest that p56(lck) may be the physiological regulator of type II PtdIns 4-kinase.

Purification and characterization of a type II phosphatidylinositol 4-kinase from rat spleen and comparison with a PtdIns 4-kinase from lymphocytes

A PtdIns 4-kinase from rat spleen particulate fraction was purified to homogeneity and its molecular properties were compared with a PtdIns 4-kinase from splenic lymphocytes. The enzyme activity was solubilized from spleen particulate fraction with Triton X-100 and chromatographed sequentially on phosphocellulose, DEAE-sephacel, heparin acrylamide and hydroxyapatite columns. The purified enzyme preparation showed a 55 kDa band on SDS-PAGE with silver staining. Renaturation of the enzyme activity from SDS-PAGE showed that it comigrated with the 55 kDa protein. Characterization of the enzyme showed that it was a type II PtdIns 4-kinase. Polyclonal antibodies raised against PtdIns 4-kinase inhibited the enzyme activity in in vitro assays. Analysis of adult rat tissue particulate fractions on immunoblots showed restricted immunoreactivity among PtdIns 4-kinases. However, the immunoreactivity is conserved in lymphoid tissues from mouse to human, suggesting that lymphoid tissue has a distinct PtdIns 4-kinase. Activation of rat splenocytes with Con A showed two fold increase in PtdIns 4-kinase activity. Comparison of PtdIns 4-kinases from spleen and splenic lymphocytes showed identical chromatographic behaviour, molecular mass, immunoreactivity, K(m) values for PtdIns and inhibition by adenosine.

Protein tyrosine phosphorylation activates rat splenic type II phosphatidylinositol 4-kinase in vitro

Regulation of phosphatidylinositol 4-kinase (PtdIns 4-kinase) by protein tyrosine phosphorylation has been indirect and the effects of phosphorylation are debatable. Rat splenic type II PtdIns 4-kinase was phosphorylated in vitro with protein tyrosine kinases from Con A stimulated splenic lymphocytes. Stoichiometric analysis showed one mole of phosphate was incorporated per mole of PtdIns 4-kinase. Tyrosine phosphorylation increased the enzyme activity by 3-fold. Kinetic analysis showed a reduction in Km for PtdIns and an increase in Vmax. Dephosphorylation with protein phosphotyrosine phosphatase abolished the activation of PtdIns 4-kinase while protein phosphatase 2A had no effect. Protein tyrosine phosphorylation and activation of PtdIns 4-kinase appear to be tissue specific.

Concanavalin A modulates tyrosine phosphorylation and activation of a type II phosphatidylinositol 4-kinase in rat splenic lymphocytes

Activation of rat splenic lymphocytes by concanavalin A resulted in two-fold increase in Ptdlns 4-kinase activity and rapid tyrosine phosphorylation of the enzyme. The activation kinetics showed a strong correlation with tyrosine phosphorylation state of the enzyme. Characterization of the enzyme activity suggests that it is a type II PtdIns 4-kinase. Kinetic analysis of the enzyme reaction showed three-fold decrease in Km for PtdIns and two-fold increase in Vmax in Con A stimulated cells. These results suggest that a type II PtdIns 4-kinase is an integral component of the early signal transduction machinery during T-cell activation by concanavalin A and is actively regulated by protein tyrosine phosphorylation-dephosphorylation.

Analysis of sequences regulating larval expression of the Adh gene of Drosophila melanogaster

The effects of a series of eight, 50 base pair internal deletions in the 5' region upstream of the proximal transcription start site of the Adh gene of Drosophila melanogaster were examined in a quantitative assay. Mixtures of two plasmids, one bearing a deleted gene, the other with an intact reference gene, were injected into alcohol dehydrogenase-negative embryos. Third instar larvae of the injected generation were assayed for relative alcohol dehydrogenase enzyme activity. Quantitative analysis of the eight deletions indicated that two regions were required for any detectable enzyme activity and one region was required for appropriate tissue specificity. The remaining five deletions significantly decreased, but did not eliminate activity. When the deleted genes were placed on a plasmid with an intact reference gene, activities of all but one deletion were restored to levels equivalent to that of the intact reference gene (regardless of orientation). This restoration of activity did not occur when the regulatory region of the intact gene was replaced with the Hsp70 heat shock promoter nor when the 50-base pair deletion encompassed the region that includes the TATA sequence. The fact that seven of the eight deleted genes express activity in the presence of a reference gene on the same plasmid suggests that the deleted gene is controlled by regulatory elements in the reference gene. Further, these regulatory elements exhibit no preference for their own, more proximate, promoter.

Purification and reconstitution of phosphatidylinositol 4-kinase from human erythrocytes

A membrane-bound phosphatidylinositol 4-kinase (PtdIns kinase) has been purified to apparent homogeneity from human erythrocytes. Enzyme activity was solubilized from urea-KCl-stripped, inside-out membrane vesicles by 3% Triton X-100. Purification to apparent homogeneity was accomplished by cation-exchange chromatography on phosphocellulose, followed by heparin-acrylamide chromatography. This resulted in a nearly 3900-fold purification of PtdIns kinase activity to a specific activity of 44 nmol min-1 mg-1. The purified enzyme has an Mr of 59,000 on silver-stained SDS-PAGE; however, many preparations also contain 54 kDa and 50 kDa proteins which are related to the 59 kDa protein and have PtdIns kinase activity. Kinetic analysis of the PtdIns kinase indicate apparent Km values of 40 and 35 microM for phosphatidylinositol and ATP, respectively. The purified enzyme has been reconstituted into phospholipid liposomes and shown to phosphorylate phosphatidylinositol.

Phosphorylation of protein 4.1 on tyrosine-418 modulates its function in vitro

Protein 4.1 was initially characterized as a protein that regulates cytoskeletal assembly in erythrocytes. However, recent studies have shown that protein 4.1 is ubiquitous in mammalian cells. Here, we show that protein 4.1 is phosphorylated on tyrosine by the epidermal growth factor receptor (EGFR) tyrosine kinase. The phosphorylation site has been localized to the 8-kDa domain, which has one tyrosine, tyrosine-418. The 8-kDa region is required for the assembly of the spectrin/actin complex, and phosphorylation by EGFR reduced the ability of protein 4.1 to promote the assembly of the spectrin/actin/protein 4.1 ternary complex. Immunoblotting with anti-phosphotyrosine antibodies showed that purified protein 4.1 contained phosphorylated tyrosine, and this increased upon phosphorylation by EGFR. This suggests that tyrosine phosphorylation of protein 4.1 occurs in vivo and may be functionally significant. The tyrosine phosphorylation site is in the center of a sequence motif that is expressed by a differentiation-specific splicing mechanism.

Purification and characterization of a protein-phosphotyrosine phosphatase from rat spleen which dephosphorylates and inactivates a tyrosine-specific protein kinase

A particulate form of protein-phosphotyrosine phosphatase was solubilized and purified over 2,000-fold from the particulate fraction of rat spleen. Phosphorylated poly(Glu, Tyr), a random copolymer of glutamic acid and tyrosine, was used as substrate for measuring protein-phosphotyrosine phosphatase activity. Nonionic detergents like Triton X-100 increased the protein-phosphotyrosine phosphatase activity of the particulate fraction (but not of the soluble fraction) by 4-8-fold. Chromatography of the Triton extract of the particulate fraction on DEAE-Sephacel gave three peaks of protein-phosphotyrosine phosphatase activity. The major peak of activity was further purified on Bio-Gel HTP, Sephadex G-75, and phosphocellulose columns. On polyacrylamide gel electrophoresis in the presence of Na-dodecyl-SO4 the purified enzyme showed a major protein band of Mr 36,000 which comigrated with enzyme activity on the phosphocellulose column. The apparent Vmax and Km for phosphorylated poly(Glu,Tyr) were 6,150 nmol min-1 mg-1 and 1.6 microM, respectively. This enzyme was strongly inhibited by microM concentrations of orthovanadate and zinc acetate. Fluoride (50 mM) inhibited this enzyme only by 30-40%. Divalent metal ions Ca2+, Mg2+, and Mn2+ were inhibitory at 1-10 mM concentration. EDTA had no effect on the activity of the purified enzyme. This phosphatase could dephosphorylate and inactivate the phosphorylated form of a tyrosine-specific protein kinase (TK-I) previously purified from rat spleen. Dephosphorylation and inactivation of TK-I by purified phosphatase were inhibited by orthovanadate. After dephosphorylation and inactivation by phosphatase, TK-I could be rephosphorylated and reactivated on incubation with ATP. These results suggest that this protein-phosphotyrosine phosphatase may be involved in the regulation of the kinase activity of TK-I.

Analysis of Adh gene regulation in Drosophila: studies using somatic transformation

We have used in vitro mutagenesis and somatic transformation [Sofer and Martin, 1987a; Martin et al., 1986] to investigate the role of cis-acting sequences in the control of alcohol dehydrogenase gene expression in larvae of Drosophila melanogaster. Two sets of experiments were carried out. In the first, a series of deletions were constructed in the region upstream of the proximal transcriptional start site. In the second, one or both introns were removed from within the structural gene. These constructs (on circular plasmids) were injected into Adh-null embryos and ADH activity was assayed in third instar larvae of the injected generation. The first set of experiments indicated that there are at least three distinct regulatory regions essential for larval activity located in the 5' flanking region of the gene. One, in an area that includes the TATA box, was found to be necessary but not sufficient for larval ADH activity. Two others, further upstream, seemed to have enhancer-like properties because their absence could be compensated by a second copy of the Adh gene on the same plasmid molecule. The second set of experiments showed that neither the tissue distribution nor amount of ADH activity was affected by the removal of one or both introns from the Adh gene.

Purification and characterization of a tyrosine-specific protein kinase of Mr 60,000 and comparison with a kinase of Mr 56,000 from rat spleen

A tyrosine-specific protein kinase of Mr 60,000 (TK-I) was purified to near homogeneity from the particulate fraction of rat spleen. The purification procedure involved sequential chromatography of the detergent-solubilized enzyme on DEAE-Sephacel and hydroxyapatite columns. Polyacrylamide-gel electrophoresis under denaturing conditions showed one major polypeptide, of Mr 60,000. Gel filtration of the enzyme on Sephacryl S-200 column showed a single peak of kinase activity, of apparent Mr 60,000. On incubation with [gamma-32P]ATP, it showed a phosphoprotein of Mr 60,000 as a result of autophosphorylation. The autophosphorylation of the kinase occurred only at tyrosine residues. Incubation of TK-I with ATP (but not with ADP) resulted in an increase in its tyrosine-specific protein kinase activity. The time course of autophosphorylation of TK-I was very similar to the time course of activation by ATP. These and other experiments suggest that autophosphorylation might be responsible for activation of TK-I observed on incubation with ATP. A second tyrosine-specific protein kinase (TK-II) was isolated from the particulate fraction of rat spleen. A highly purified preparation of TK-II on incubation with [gamma-32P]ATP gave a major phosphoprotein, of Mr 56,000. TK-II was different from TK-I in several properties: (a) substrate specificity; (b) chromatographic behaviour; (c) phosphopeptide maps; and (d) inhibition by tosyl-lysylchloromethane. Antisera raised against TK-I did not cross-react with TK-II. These results suggest that TK-I and TK-II are distinct proteins, perhaps coded by two different genes.

Activation of a cellular tyrosine-specific protein kinase by phosphorylation

A tyrosine-specific protein kinase of Mr 56 000 was purified over 200-fold from rat spleen. Incubation of this kinase preparation with ATP and Mg2+ results in about 10-fold increase in the protein kinase activity. The activation of the kinase was unaffected in the presence of soybean trypsin inhibitor. Polyacrylamide gel electrophoresis of the enzyme preparation after phosphorylation with ATP showed one phosphoprotein band of Mr 56 000. During purification of this kinase a large decrease in enzyme activity was observed which could be prevented by adding 10 microM vanadate, as inhibitor of tyrosine-specific protein phosphatases. These results suggest that the activation of the protein kinase by ATP is due to phosphorylation of the enzyme.

Comparison of tryptic peptide profiles of alcohol dehydrogenase from Drosophila melanogaster at different ages: a rapid procedure using high performance liquid chromatography

Age-related changes in the primary structure of alcohol dehydrogenase (ADH) from three different strains (Adh-F, Adh-D and Adh-S) of Drosophila melanogaster have been investigated by tryptic peptide analysis. The procedure involves isolation of 14C-labelled ADH, immunoprecipitation and HPLC separation of tryptic peptides. This method is rapid, reproducible and sensitive. By using this procedure it is demonstrated that there are no significant differences between the ADH tryptic peptide profiles of young (10-day-old) and old (50-day-old) flies. The usefulness of this procedure for screening mutant and variant enzymes is discussed.