Porphobilinogen deaminase is encoded by a single gene in Arabidopsis thaliana and is targeted to the chloroplasts

Porphobilinogen deaminase (PBG deaminase) is an early enzyme of the pathway for chlorophyll and heme synthesis. Using degenerate oligonucleotide primers, based on amino acid sequence data for purified PBG deaminase from pea, a fragment was amplified from Arabidopsis genomic DNA by PCR, and then used to isolate both a cDNA and a genomic clone for PBG deaminase from Arabidopsis. The cDNA, shown to be full-length by primer extension, encodes a precursor protein of 382 residues, which can be imported into isolated chloroplasts and processed to the mature size. The genomic clone encodes an identical sequence to the cDNA, except for the presence of four introns within the coding region of the mature protein, and 1.7 kb of upstream sequence. There is no obvious TATA box within 50 bp of the transcription start. Southern blot analysis suggests that PBG deaminase is encoded by a single gene in the Arabidopsis genome, and RNase protection experiments demonstrated that this gene is expressed in both leaves and roots. These results support the conclusion that there is only one form of PBG deaminase in all plant cells, which is located in the plastid.

Pathological mechanisms of hepatic tumour formation in rats exposed chronically to dietary hexachlorobenzene

The chronic dietary administration of hexachlorobenzene (HCB) to rats for a year or more results in the formation of liver tumours described as hepatocellular carcinomas, hepatomas or haemangiomas. The hepatotoxicity of HCB, which is greatest in hamsters and rats, gives rise to peliosis and necrosis with haemosiderosis. This pattern of hepatotoxicity indicates vascular damage, which through haemosiderosis could increase not only the toxic effect of HCB to hepatocytes but also its tumourogenic potential. The present study confirmed vascular damage by the identification of widespread fibrin deposits in the livers of rats chronically exposed to HCB, using an antibody to rat fibrin. Based on our study we suggest that the formation of hepatomas and haemangiomas with elements of peliosis (cystic blood-filled cavities) could be explained by the compensatory hyperplastic responses to hepatocellular necrosis and by the simultaneous loss of hepatocellular cords. The accumulation of iron in the liver would strongly potentiate the development of hepatic tumours, as has been found in HCB and polychlorinated biphenyl-treated mice with iron overload. The implications of this non-genotoxic mechanism of hepatoma formation for the assessment of human health risk are discussed.

Potentiation of iron accumulation in cardiac myocytes during the treatment of iron overload in gerbils with the hydroxypyridinone iron chelator CP94

Gerbils administered iron dextran are the only animal species which have been shown to develop hemochromatosis of the liver and heart in the same manner as transfusion dependent homozygous thalassemics. The iron chelating hydroxypyridinone, CP94, has been administered prophylactically to iron overloaded gerbils in a dosing regime which favors the formation of bidentate chelated iron, to examine the possibility of additional toxicity being caused to the liver and heart by the bidentate chelated iron complex. Hepatic iron accumulation was inhibited by CP94 administration for up to 6 weeks, but not after 20 weeks. Iron accumulation in the heart was increased significantly after 6 and 20 weeks of chelator treatment. Pathological changes in both organs were markedly more severe after 20 weeks in chelator treated animals. There was a higher incidence of cardiofibrosis and more extensive liver fibrosis in iron overloaded, chelator treated animals after 20 weeks.

Analysis of HLA-B*44 alleles encoded on extended HLA haplotypes by direct automated sequencing

We developed a PCR-based approach to sequence exons 2 and 3 of HLA-B44 alleles from genomic DNA. We applied this method to determine the B44 alleles encoded on extended HLA-A, B, DRB1, DQB1 haplotypes and the degree of mismatching for B44 alleles among marrow transplant patients and their unrelated donors (URD). A total of 81 samples was studied and included 38 patients, 42 donors and the cell "FMB"; the 80 clinical samples were comprised of 8 unpaired patients, 12 unpaired donors, and 30 URD-recipient pairs. Three alleles encoding B44 were identified, B*4402 (N = 51), 4403 (N = 32) and a new allele designated B*44KB and named B*4405 (N = 4). Of the 27 patients for whom family study was available, there were 13 different B*4402, 7 different B*4403 and 2 new B*4405 haplotypes. HLA-A2, Cw*0501, B*4402, DRB1*0401, DQB1*0301 (n = 2); A2, Cw*0501, B*4402, DRB1*1501, DRB5*0101, DQB1*0602 (n = 2); and HLA-A29, Cw*1601, B*4403, DRB1*0701, DQB1*0201 (n = 5) comprised the most common patient haplotypes. Of 30 URD-recipient transplant pairs studied, 27 were HLA-A, B serologically matched and DRB1, DRB3, DRB5, DQB1 allele matched, and 3 pairs were DRB1-mismatched. All B44 allele mismatching (N = 3) occurred among the 27 matched pairs. The novel B*4402-variant sequence, HLA-B*4405, was identified in 4 individuals, and in each case was associated with an HLA-B44, Cw*02022, DRB1*0101, DQB1*0501 haplotype. HLA-B*4405 and B*4402 are identical in exon 2; in exon 3 however, B*4405 encodes T instead of G at nucleotide position 75 which translates to a substitution of tyrosine for aspartic acid at codon 116.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of iron on the induction of hepatic tumors and porphyria by octachlorostyrene in C57BL/10ScSn mice

Octachlorostyrene (OCS) is an environmental contaminant, present in fish of Northern European waters and the Great Lakes of America. It has many distribution and toxic similarities to hexachlorobenzene (HCB). Administration of OCS at 0.01% of the diet to C57BL/10ScSn mice within iron overload for 18 months gave only a low incidence of hepatic nodular hyperplasia (2/10 survivors) and no hepatocellular adenomas or carcinomas. In contrast, with a similar regime, HCB causes severe liver cancer or nodules in all exposed mice. Whole body autoradiography of mice given [14C]OCS or [14C]HCB showed no gross variations in distribution or covalent binding of the radiolabelled compound to account for the difference between the chemicals in the development of tumours. In 12-week studies, the CYP1A subfamily was induced to a greater degree by HCB than OCS and iron-enhanced uroporphyria was significantly greater with HCB. The findings are consistent with the proposal that uroporphyria and liver cancer induced in mice by HCB are associated through related mechanisms, but occur to a significantly lesser extent with OCS.

Isolation of a cDNA encoding chloroplast ferrochelatase from Arabidopsis thaliana by functional complementation of a yeast mutant

Ferrochelatase catalyzes the insertion of ferrous iron into protoporphyrin IX to form protoheme. It is located in the mitochondria in all eukaryotes and is also found in plastids in plants. Although it has been purified from animals and microorganisms, and genes for it isolated and characterized, very little is known about plant ferrochelatases. We have isolated a cDNA for ferrochelatase from the higher plant Arabidopsis thaliana by functional complementation of a mutant of Saccharomyces cerevisiae defective in this enzyme. The cDNA encodes a protein of 52 kDa, which has 25-35% sequence similarity to ferrochelatases from other organisms. There is an N-terminal extension of about 65 residues, which is almost certainly the chloroplast transit peptide, since the precursor protein, transcribed and translated in vitro, is efficiently imported and processed to the mature size by isolated pea chloroplasts. In contrast, the precursor was not processed by mitochondrial processing peptidase activity, nor could import into isolated yeast mitochondria be demonstrated conclusively, although, presumably, in the rescued yeast mutant, at least some of the Arabidopsis ferrochelatase must be present in the mitochondria. A single transcript the same size as the cDNA was detected in both Arabidopsis leaves and roots, although the amount of message was greater in the photosynthetic tissue. Southern analysis suggests that there is a single gene for chloroplast ferrochelatase in Arabidopsis.

Follicular toxic pustuloderma associated with allopurinol

Allopurinol is widely prescribed for primary and secondary hyperuricaemia, and cutaneous adverse reactions are seen in 0.8-2.1% of recipients. The majority of these are mild and include pruritus, diffuse or maculo-papular erythema, urticaria and ichthyosis. More severe reactions are well recognized and include exfoliative dermatitis, toxic epidermal necrolysis and a generalized hypersensitivity syndrome. The latter typically comprises fever, rash, hepatic and renal dysfunction and eosinophil leucocytosis. The occurrence of toxic pustuloderma due to allopurinol, confirmed by re-challenge, is reported.

The effect of nerve growth factor, ciliary neurotrophic factor, and ACTH analogs on cisplatin neurotoxicity in vitro

Cisplatin, used to treat ovarian, bladder, and testicular cancers, causes a sensory dose-limiting neuropathy. Preliminary observations in humans and animals suggest that nerve damage may be prevented by ACTH analogs, particularly those belonging to the melanocortin class, and by nerve growth factor (NGF). We established a rat embryo dorsal root ganglion model to study cisplatin neurotoxicity. The drug reproducibly inhibited axonal growth at concentrations similar to that known to produce toxicity in neurons. The inhibition was prevented in a dose-dependent fashion by simultaneous exposure to alpha-melanocyte stimulating hormone (alpha-MSH) or ACTH but not by excess NGF or ciliary neurotrophic factor (CNTF). The ACTH peptides were not effective in preventing suramin-induced neurotoxicity in the same model. Drug interaction and dose-response studies showed that ACTH and alpha-MSH do not act by potentiation of NGF action. ACTH analogs appear to protect against cisplatin-induced neurotoxicity directly at the cellular level.

Assessment of proliferative activity in leukaemic bone marrow using the monoclonal antibody Ki-67

AIMS

To investigate proliferative activity in leukaemic and lymphomatous bone marrow infiltrates and to assess the feasibility of transport of specimens among institutions.

METHODS

Proliferative activity in bone marrow trephine cryosections from 99 patients with non-Hodgkin's lymphoma (NHL), 23 patients with acute myeloid leukaemia (AML), 11 with acute lymphoblastic leukaemia (ALL), and two with acute undifferentiated leukaemia (AUL) was investigated. Infiltration was seen in 52 out of 99 cases of NHL on bone marrow cryosections. A score was devised to assess pathological infiltrates in bone marrow trephine cryosections using the monoclonal antibody Ki-67. This method of scoring gave a measure of non-erythroid proliferative activity.

RESULTS

Mean Ki-67 positivity in bone marrow infiltrates in 31 low grade B cell lymphomas (Kiel classification) was 0.3% before and 4.7% after treatment, 16.4% in seven high grade B cell lymphomas, and 17.8% in 12 peripheral T cell lymphomas. In 48 cases of NHL, bone marrow cryosections had not been infiltrated, and in all but one case the percentage of Ki-67 positive cells in normal marrow was less than 3%; the remaining case showed coexistent myelodysplasia and 8% bone marrow Ki-67 positivity. In eight cases of common ALL at diagnosis, the mean Ki-67 positivity in marrow cryosections was 24.9%, significantly higher than the 2.4% Ki-67 positivity seen in AML (p < 0.05). One of the two cases of common ALL with less than 1% Ki-67 positivity was refractory to treatment.

CONCLUSIONS

Proliferative activity of erythroid elements in the bone marrow varies greatly. Immunostaining of bone marrow cryosections using Ki-67 permits accurate assessment of non-erythroid proliferative activity in lymphomas and leukaemia. High grade B cell lymphomas and peripheral T cell lymphomas invading the marrow have very similar mean proliferative activities. Such levels of proliferation are of the same order as those seen in common ALL, but much higher than those seen in AML.

Cloning and characterization of Tag 1, a tobacco anther beta-1,3-glucanase expressed during tetrad dissolution

A critical stage in pollen development is the dissolution of the four products of meiosis, the tetrads, into free microspores. The tetrads are surrounded by a thick callose wall composed of beta-1,3-glucan. At the completion of meiosis, the tetrads are released into the anther locule after hydrolysis of the callose by a beta-1,3-glucanase. Using the polymerase chain reaction, we have amplified and subsequently cloned a cDNA corresponding to a beta-1,3-glucanase, tobacco (Nicotiana tabacum cv. Samsun) anther glucanase (Tag 1), which is expressed exclusively in anthers from meiosis to the free microspore stage of pollen development. The identity of the clone was determined by DNA and deduced protein sequence similarity to other known beta-1,3-glucanases. Several regions strictly conserved among four classes of glucanases are also conserved in the Tag 1 protein. Tag 1 represents a novel class of beta-1,3-glucanase based on phylogenetic analysis and RNA expression pattern. Tag 1 RNA was detected in situ only in the tapetum, with maximal expression just prior to tetrad dissolution. Due to its expression pattern and sequence similarity to other beta-1,3-glucanases, we believe Tag 1 may be involved in tetrad dissolution.

Cloning and characterisation of genes for tetrapyrrole biosynthesis from the cyanobacterium Anacystis nidulans R2

The genes for 5-aminolevulinic acid dehydratase (ALAD) and uroporphyrinogen III synthase (UROS), two enzymes in the biosynthetic pathway for tetrapyrroles, were independently isolated from a plasmid-based genomic library of Anacystis nidulans R2 (also called Synechococcus sp. PCC7942), by their ability to complement Escherichia coli strains carrying mutations in the equivalent genes (hemB and hemD respectively). The identity of the genes was confirmed by comparing the appropriate enzyme activities in complemented and mutant strains. Subclones of the original plasmids that were also capable of complementing the mutants were sequenced. The inferred amino acid sequence of the cyanobacterial HemB protein indicates a significant difference in the metal cofactor requirement from the higher-plant enzymes, which was confirmed by overexpression and biochemical analysis. The organisation of the cyanobacterial hemD locus differs markedly from other prokaryotes. Two open reading frames were found immediately upstream of hemD. The product of one shows considerable similarity to published sequences from other organisms for uroporphyrinogen III methylase (UROM), an enzyme involved in the production of sirohaem and cobalamins (including vitamin B-12). The product of the other shows motifs which are similar to those found in proteins responsible for metabolic regulation in yeast and indicates that this family of transcription control proteins, which has previously been reported only from eukaryotes, is also represented in prokaryotes.

Halogenated Terpenoids. XXVIII. The Conversion of Limonene Tetrabromide Into Carvone Derivatives With Retained C8 Stereochemistry

Limonene tetrabromide has been converted into the corresponding carvone derivative with retention of the C8 stereochemistry, thus allowing the C8 stereochemistry of the limonene and carvone series to be chemically correlated.

The responsiveness of embryonic stem cells to alpha and beta interferons provides the basis of an inducible expression system for analysis of developmental control genes

Embryonic stem (ES) cells, derived from the inner cell mass of the preimplantation mouse embryo, are used increasingly as an experimental tool for the investigation of early mammalian development. The differentiation of these cells in vitro can be used as an assay for factors that regulate early developmental decisions in the embryo, while the effects of altered gene expression during early embryogenesis can be analyzed in chimeric mice generated from modified ES cells. The experimental versatility of ES cells would be significantly increased by the development of systems which allow precise control of heterologous gene expression. In this paper, we report that ES cells are responsive to alpha and beta interferons (IFNs). This property has been exploited for the development of inducible ES cell expression vectors, using the promoter of the human IFN-inducible gene, 6-16. The properties of these vectors have been analyzed in both transiently and stably transfected ES cells. Expression was minimal or absent in unstimulated ES cells, could be stimulated up to 100-fold by treatment of the cells with IFN, and increased in linear fashion with increasing levels of IFN. High levels of induced expression were maintained for extended periods of time in the continuous presence of the inducing signal or following a 12-h pulse with IFN. Treatment of ES cells with IFN did not affect their growth or differentiation in vitro or compromise their developmental potential. This combination of features makes the 6-16-based expression vectors suitable for the functional analysis of developmental control control genes in ES cells.

Idarubicin for remission induction of acute myeloid leukemia: United Kingdom multicenter experience

Ninety-eight adult patients with acute myeloid leukemia were given variable remission induction/consolidation regimens containing idarubicin. Sixty-nine (70%) were new cases (median age, 56 years) and 29 (30%) were in relapse (n = 24) or had primary refractory disease (n = 5) (median age, 46 years). Complete remission (CR) rates were 57% (39 of 69 patients) of the newly diagnosed patients, with no difference for those below or above 55 years of age (56% v 59%) or for patients exhibiting white blood cell counts of less or more than 50 x 10(9)/L (52% v 69%; P = .8). Of the 39 patients who achieved CR, 26 (67%, 38% of the total number of patients) remain in CR with a median follow-up of 3 months (range, 0 to 61 months). Forty-two percent of the relapsed cases (10 of 24 patients) and 60% of the primary refractory disease cases (three of five patients) achieved CR. Of these 13 responders, six are alive (three continuing in CR and three relapsed) with a median follow-up of 3 months (range, 1 to 20 months), and seven have died with a median survival of 7 months (range, 0 to 12 months). Of the 52 patients who have achieved CR, 84% did so with one course of treatment and 16% with two courses. The presence of normal cytogenetic analysis or favorable chromosomal aberrations significantly improved overall CR rates. The patients in this study had significantly more unfavorable cytogenetic abnormalities than the historic controls. Reported toxicity was hepatic in 13%, cardiac in 9%, and renal in 7% of all cases. These data suggest a comparable efficacy of idarubicin to other anthracyclines in remission induction of acute myeloid leukemia, with a promising role in relapsed/refractory disease.

Molecular characterization of a gene encoding a cysteine-rich protein preferentially expressed in anthers of Lycopersicon esculentum

The tomato (Lycopersicon esculentum Mill.) cDNA clone TomA5B was isolated by differential screening of a cDNA library prepared from anthers at late meiosis to tetrad formation. The 5B gene is present in a single copy in the tomato genome. Expression is developmentally regulated and tissue specific. RNA accumulation was detected from premeiosis through tetrad release in the tapetal cell layer of the anther with low levels of RNA detected in petals and early stages of pistil development. The protein deduced from the DNA sequence analysis is predicted to have a molecular mass of 11.1 kDa and a secretory signal sequence, suggesting it is a secreted protein. The deduced 5B protein has a pattern of cysteine residues that is similar to other proteins that have stamen-specific expression and to a superfamily of seed proteins. The 5B protein is unique in that there is no amino acid sequence similarity to other proteins beyond the similar cysteine motif.

Suspected cutaneous drug toxicity in rheumatoid arthritis--an evaluation

Cutaneous toxicity from drugs used to treat RA is a major perceived problem. Over a 2-yr period we have prospectively reviewed 114 patients with a suspected adverse cutaneous reaction to anti-rheumatic drugs. In 71 (62%), the rash was thought to be unrelated to drug therapy. This group included 10 in whom the rash had resolved before review (usually < 1 week), 38 with a rash related to their rheumatoid disease and 23 with eruptions unrelated to either drugs or arthritis. Forty-three (38%) patients had rashes thought to be related to their drug therapy. Gold therapy (both oral and intramuscular) was implicated most frequently (31 patients). However, the majority of these (23) had a pityriasiform/discoid eczematous eruption that responded to potent topical steroids occasionally with a reduction in gold dosage. In this sample it was possible to continue drug therapy in 82% of patients with what were initially thought to be cutaneous adverse drug reactions. Careful evaluation should allow a majority of patients to continue drug therapy from which they are often gaining benefit.