Dietary arachidonic acid increases eicosanoid production in the presence of equal amounts of dietary eicosapentaenoic acid

Previously, we demonstrated that dietary n-3 PUFA (1.5%, w/w) effectively inhibited the production of eicosanoids derived from tissue arachidonic acid (AA) (Whelan et al., 1991). More recently, we also reported that dietary AA (1.0%, w/w) significantly augmented platelet and macrophage eicosanoid production in vitro (Whelan et al., 1993). This present study was designed to investigate the antithetic relationship of dietary AA and EPA on eicosanoid production in vivo. Forty-nine CD-1 male mice were randomly divided into four dietary groups. Identical diets were supplemented with ethyl esters (1.5%, w/w) of the following fatty acids: oleic acid (OA), AA, EPA or AA + EPA (A + E). After four weeks on diet, peritoneal cells were stimulated in vivo with opsonized zymosan and analyzed for eicosanoid production (PGE2, 6-keto-PGF1a, TXB2, LTE4, LTB4, LTE5 and LTB5). The pooled eicosanoid production in the AA group was 41% and 300% higher compared to the OA (control) and EPA groups, respectively. Pooled eicosanoid production in the EPA group was 47% that of the OA group. When equivalent amounts of AA and EPA (AA + EPA) were included in the diet, the pooled eicosanoid production was 29% and 274% higher compared to the OA and EPA groups, respectively. These data demonstrate that dietary AA (1) enhances eicosanoid production in vivo and (2) abrogates virtually all of the effects observed with dietary EPA when both are included in the diet. The clinical implications of dietary AA as modulated by increased eicosanoid production could be significant, particularly when n-3 PUFA are used to reduce eicosanoid-mediated events.

Random mutagenesis of human estrogen receptor ligand binding domain identifies mutations that decrease sensitivity to estradiol and increase sensitivity to a diphenol indene-ol compound: basis for a regulatable expression system

We have used low fidelity polymerase chain reaction amplification to generate mutations in the human estrogen receptor ligand binding domain (LBD). Screening of libraries of mutants in yeast revealed a variety of phenotypic changes including decreased responsiveness to estradiol and increased responsiveness to synthetic compounds. Identification of the mutations responsible for these phenotypic changes indicated discrete regions of the LBD that are important for human estrogen receptor function. Cumulative rounds of mutagenesis and screening allowed us to produce a mutant estrogen receptor that was of reversed specificity as compared with the wild type LBD, in that it was more responsive to a diphenol indene-ol than to estradiol. This mutant may form the basis of a useful regulatable expression system in mammalian cells.

A matrix-located processing peptidase of plant mitochondria

Nuclear-encoded mitochondrial precursor proteins are proteolytically processed inside the mitochondrion after import. The general mitochondrial processing activity in plant mitochondria has been shown to be integrated into the cytochrome bc1 complex of the respiratory chain. Here we investigate the occurrence of an additional, matrix-located processing activity by incubation of the precursors of the soybean mitochondrial proteins, alternative oxidase, the FAd subunit of the ATP synthetase and the tobacco F1 beta subunit of the ATP synthase, with the membrane and soluble components of mitochondria isolated from soybean cotyledons and spinach leaves. A matrix-located peptidase specifically processed the precursors to the predicted mature form in a reaction which was sensitive to orthophenanthroline, a characteristic inhibitor of mitochondrial processing peptidase (MPP). The specificity of the matrix peptidase was illustrated by the inhibition of processing of the alternative oxidase precursor in both soybean and spinach matrix extracts upon altering a single amino acid residue in the targeting presequence (-2 Arg to Gly). Additionally, there was no evidence for general proteolysis of precursor proteins incubated with the matrix. The purity of the matrix fractions was ascertained by spectrophotometric and immunological analyses. The results demonstrate that there is a specific processing activity in the matrix of soybean and spinach in addition to the previously well characterized membrane-bound MPP integrated into the cytochrome bcl complex of the respiratory chain.

Sulindac causes rapid regression of preexisting tumors in Min/+ mice independent of prostaglandin biosynthesis

Several lines of evidence strongly link prostaglandins (PGs) and leukotrienes (LTs) to cancer of the intestine. Several studies have reported a 40-50% reduction in mortality from colorectal cancer in individuals who routinely consume nonsteroidal anti-inflammatory drugs, possibly by inhibiting cyclooxygenase activity. However, the role of eicosanoids in this process is still unclear. The heterozygote Min/+ mouse model, like patients with familial adenomatous polyposis, carries a nonsense mutation in the adenomatous polyposis coli (APC) gene that results in the spontaneous development of intestinal adenomas (100% incidence). This study investigated the association between eicosanoid biosynthesis, intestinal tumor load, and the chemotherapeutic effect of the nonsteroidal anti-inflammatory drug sulindac during early and preexisting phases of tumor growth and development as well as residual effects after drug withdrawal. Administration of sulindac (320 ppm) to Min/+ mice reduced the tumor number by 95% but did not alter the levels of PGE2 and LTB4 in intestinal tissues. Increasing PGE2 and LTB4 levels by 44% with dietary arachidonic acid supplementation had no effect on tumor number or size. When sulindac was added to the arachidonic acid-supplemented diet, tumor number was reduced by 82%, whereas eicosanoid levels remained elevated. In Min/+ mice with established tumors, treatment with sulindac for 4 days reduced tumor number by 75%, and continual administration of sulindac was necessary to maintain a reduced tumor load. In summary, alterations in eicosanoid formation were not correlated with tumor number or size in the Min/+ mouse model; thus, the antitumor effect of sulindac seems to be PG independent.

Temporal regulation of in vitro import of precursor proteins into tobacco mitochondria

Protein import into isolated tobacco mitochondria was investigated using mitochondria from leaves harvested at different times of the day and night. Efficient import was only detected with mitochondria isolated from leaves harvested during the dark period of the growth cycle, only low levels of import were detected from leaves harvested during the light period. However, this temporal difference seen in import did not appear to be circadian in nature. This implies that the protein import process in mitochondria isolated from leaves is not constitutive. This has important implications for targeting specificity studies performed in transgenic plants, as unless the plants are tested at the time when import is occurring, the true in vivo targeting abilities of chimeric constructs will not be measured.

Tissue-specific pattern of stress kinase activation in ischemic/reperfused heart and kidney

In this report we investigate the molecular mechanisms that contribute to tissue damage following ischemia and ischemia coupled with reperfusion (ischemia/reperfusion) in the rat heart and kidney. We observe the activation of three stress-inducible mitogen-activated protein (MAP) kinases in these tissues: p38 MAP kinase and the 46- and 55-kDa isoforms of Jun N-terminal kinase (JNK46 and JNK55). The heart and kidney show distinct time courses in the activation of p38 MAP kinase during ischemia but no activation of either JNK46 or JNK55. These two tissues also respond differently to ischemia/reperfusion. In the heart we observe activation of JNK55 and p38 MAP kinase, whereas in the kidney all three kinases are active. We also examined the expression pattern of two stress-responsive genes, c-Jun and ATF3. Our results indicate that in the heart both genes are induced by ischemia and ischemia/reperfusion. However, in the kidney c-Jun and ATF3 expression is induced only by ischemia/reperfusion. To correlate these molecular events with tissue damage we examined DNA laddering, a common marker of apoptosis. A significant increase in DNA laddering was evident in both heart and kidney following ischemia/reperfusion and correlated with the pattern of kinase activation, supporting a link between stress kinase activation and apoptotic cell death in these tissues.

Dietary fish oil and fish and borage oil suppress intrapulmonary proinflammatory eicosanoid biosynthesis and attenuate pulmonary neutrophil accumulation in endotoxic rats

OBJECTIVE

Proinflammatory eicosanoids and cytokines are important mediators of local inflammation in acute lung injury. We determined if enteral nutrition with anti-inflammatory fatty acids, eicosapentaenoic acid, and gamma-linolenic acid would reduce the intrapulmonary synthesis of proinflammatory eicosanoids and cytokines and pulmonary neutrophil accumulation in a rat model of acute lung injury.

DESIGN

Prospective, randomized, controlled, double-blind study.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Male Long-Evans rats (250 g).

INTERVENTIONS

Rats were randomly assigned to three dietary treatment groups and fed nutritionally complete diets (300 kcal/kg/day) containing 55.2% of the total calories from fat with either 97% corn oil, 20% fish oil, or 20% fish and 20% borage oil for 21 days. On day 22, bronchoalveolar lavage was performed 2 hrs after an intravenous injection of Salmonella enteritidis endotoxin (10 mg/kg) or saline. Bronchoalveolar lavage fluid was analyzed for leukotriene B4, leukotriene C4/D4, thromboxane B2, prostaglandin E2, 6 keto-prostaglandin F1alpha, tumor necrosis factor (TNF)-alpha, and macrophage inflammatory protein-2 (MIP-2). Lung myeloperoxidase activity (a marker for neutrophil accumulation) and phospholipid fatty acid composition were also determined.

MEASUREMENTS AND MAIN RESULTS

Lung phospholipid concentrations of arachidonic acid were lower and the concentrations of eicosapentaenoic acid and docosahexaenoic acid were higher with fish oil and fish and borage oil as compared with corn oil. Dihomo-gamma-linolenic acid, the desaturated and elongated intermediate of gamma-linolenic acid, increased with fish and borage oil as compared with fish oil and corn oil. The levels of leukotriene B4, leukotriene C4/D4, 6-keto-prostaglandin F1alpha, and thromboxane B2 with corn oil were significantly increased with endotoxin as compared with saline. In contrast to the corn oil group, endotoxin did not significantly increase bronchoalveolar lavage levels of leukotriene B4, leukotriene C4/D4, and thromboxane B2 above those of saline-treated rats with fish oil and fish and borage oil. Lung myeloperoxidase activity was significantly increased in endotoxin-treated rats compared with those rats given saline in all dietary treatment groups. However, lung myeloperoxidase activity was significantly lower with either fish oil or fish and borage oil as compared with corn oil after endotoxin. Although endotoxin increased the levels of TNF-alpha and MIP-2 with all dietary treatment groups as compared with saline-treated rats, there were no significant differences in the levels of either cytokine between the dietary treatment groups.

CONCLUSIONS

These results indicate that dietary fish oil and fish and borage oil as compared with corn oil may ameliorate endotoxin-induced acute lung injury by suppressing the levels of proinflammatory eicosanoids (but not TNF-alpha or MIP-2) in bronchoalveolar lavage fluid and reducing pulmonary neutrophil accumulation.

Differential expression of the multigene family encoding the soybean mitochondrial alternative oxidase

The alternative oxidase (AOX) of the soybean (Glycine max L.) inner mitochondrial membrane is encoded by a multigene family (Aox) with three known members. Here, the Aox2 and Aox3 primary translation products, deduced for cDNA analysis, were found to be 38.1 and 36.4 Kd, respectively. Direct N-terminal sequencing of partially purified AOX from cotyledons demonstrates that the mature proteins are 31.8 and 31.6 KD, respectively, implying that processing occurs upon import of these proteins into the mitochondrion. Sequence comparisons show that the processing of plant AOX proteins occurs at a characteristic site and that the AOX2 and AOX3 proteins are more similar to one another than to other AOX proteins, including soybean AOX1. Transcript analysis using a polymerase chain reaction-based assay in conjunction with immunoblot experiments indicates that soybean Aox genes are differentially expressed in a tissue-dependent manner. Moreover, the relative abundance of both Aox2 transcripts and protein in cotyledons increase upon greening of dark-grown seedlings. These results comprehensively explain the multiple AOX-banding patterns observed on immunoblots of mitochondrial proteins isolated from various soybean tissues by matching protein bands with gene products.

Progress in transcriptionally targeted and regulatable vectors for genetic therapy

Safety is an important consideration in the development of genetic therapy protocols; for example, proteins that are therapeutic in the context of one tissue may be harmful in another. This is particularly relevant to suicide gene strategies for cancer, which require in vivo delivery of DNA and which, in general, demand that the therapeutic product be limited as far as possible to malignant cells. This has led to a requirement for "transcriptionally targeted" vectors that can restrict the expression of the therapeutic sequence to appropriate cells. Furthermore, there may be a therapeutic window for certain proteins such that levels of expression below and above certain thresholds may be ineffective or toxic, respectively. Therefore, it would also be desirable to create vectors that allow exogenous control of expression, so that levels of the therapeutic protein can be raised or lowered according to therapeutic need. In the context of transcriptional targeting, one may sometimes use cis-acting sequences to limit transgene expression to the target cell type. In genetic therapy for cancer, for example, it may be possible to identify and use transcriptional control elements that drive expression of proteins unique to, or over-expressed in, malignant cells. These controls would greatly reduce collateral expression of the transgene, and hence reduce toxicity to healthy cells. With regard to exogenous control of expression subsequent to transduction, several synthetic gene regulation systems have now been produced. In these systems, an inducer or repressor acts on a synthetic transcription factor that recognizes motifs unique to the promoter of the transgene; this allows regulated expression of the therapeutic protein without nonspecific effects on cellular promoters. It is likely that a vector will soon be produced in which tissue-restricted expression of the synthetic transcription factor is combined with regulatable transgene expression thereby allowing precise control of therapeutic protein production in specific tissues via administration of an inducing or repressing agent.

Effects of eicosapentaenoic and gamma-linolenic acid on lung permeability and alveolar macrophage eicosanoid synthesis in endotoxic rats

OBJECTIVES

Proinflammatory eicosanoids (cyclooxgenase and lipoxygenase metabolites of arachidonic acid) released by alveolar macrophages play an important role in endotoxin-induced acute lung injury. We investigated the effect of prefeeding rats for 21 days with enteral diets that provided the anti-inflammatory fatty acids, eicosapentaenoic acid and gamma-linolenic acid (derived from fish oil and borage oil, respectively), as compared with an n-6 fatty acid-enriched diet (corn oil) on the following: a) lung microvascular protein permeability, arterial blood pressure, and platelet and white blood cells in a model of endotoxin-induced acute lung injury; b) alveolar macrophage prostaglandin and leukotriene synthesis; and c) liver and alveolar macrophage phospholipid fatty acid composition.

DESIGN

Prospective, randomized, controlled, double-blind study.

SETTING

Research laboratory at a university medical center.

SUBJECTS

Male Long-Evans rats, weighing 250 g.

INTERVENTIONS

Rats were randomized into four dietary treatment groups and fed nutritionally complete diets (300 kcal/kg/day), containing 55.2% of the total calories from fat with either 97% corn oil, 20% fish oil, 20% fish and 5% borage oil, or 20% fish and 20% borage oil for 21 days. On day 22, lung microvascular protein permeability, mean arterial pressure, and platelet and white blood cell counts were determined for 2 hrs after an intravenous injection of Salmonella enteritidis endotoxin (10 mg/kg). In a second group of prefed rats, the phospholipid fatty acid composition was determined in liver and alveolar macrophages. Alveolar macrophages were harvested by bronchoalveolar lavage and stimulated in vitro with a calcium ionophore (A23187), and the concentrations of leukotrienes B4 and B5, thromboxane A2, prostaglandin E2, and 6-keto-prostaglandin F1 alpha were measured in a third group of prefed rats.

MEASUREMENT AND MAIN RESULTS

Lung permeability was greatest with corn oil and was significantly attenuated with 20% fish oil and 20% fish and 5% borage oil, and this effect approached significance with 20% fish and 20% borage oil (p = .06). The early and late hypotensive effects of endotoxin were attenuated with 20% fish oil, 20% fish and 5% borage oil, and 20% fish and 20% borage oil, as compared with corn oil. Concentrations of leukotriene B4, prostaglandin E2, and thromboxane B2 released from A23187-stimulated alveolar macrophages were significantly lower with 20% fish oil and 20% fish and 20% borage oil, as compared with corn oil. The increase in lung microvascular protein permeability with 20% fish and 20% borage oil was not significantly different than the lung microvascular protein permeability that was found in animals receiving 20% fish oil (p = .20) and 20% fish and 5% borage oil (p = .31). Alveolar macrophage and liver phospholipid concentrations of arachidonic acid were lower, and the concentrations of eicosapentaenoic acid and docosahexaenic acid were higher, with 20% fish oil, and 5% borage oil, and 20% fish and 20% borage oil, as compared with corn oil. Dihomo-gamma-linolenic acid, the desaturated and elongated intermediate of gamma-linolenic acid, was increased with 20% fish and 20% borage oil, as compared with 20% fish oil and 20% fish and 5% borage oil.

CONCLUSIONS

The severity of pulmonary microvascular protein permeability and the degree of hypotension were reduced with fish or fish and borage oil diets, as compared with corn oil, in endotoxic rats. The reduced synthesis of the proinflammatory arachidonic acid-derived mediators, leukotriene B4, thromboxane B2, and prostaglandin E2 from stimulated alveolar macrophages was indicative of a decrease in arachidonic acid and an increase in eicosapentaenoic acid and docosahexaenoic acid in cell membrane phospholipids.

Distamycin prolongs E-selectin expression by interacting with a specific NF-kappaB-HMG-I(Y) binding site in the promoter

The E-selectin cell adhesion protein plays a critical role in mediating adherence of leukocytes to endothelium at sites of inflammation. Cytokine-induced E-selectin expression on the surface of endothelial cells is transient; mRNA expression peaks at 3-4 h after induction and returns to basal levels within 24 h. The mechanism for this transcriptional down-modulation is not known. Promoter binding factors responsible for induced gene expression include NF-kappaB, which binds at three sites within the E-selectin promoter, and HMG-I(Y), which binds to the A/T-rich core found at the centre of these binding sites. Distamycin is an antibiotic that also binds A/T-rich DNA and inhibits HMG-I(Y) DNA binding. To study the role of HMG-I(Y) in E-selectin expression, we have examined the effect of distamycin on the cytokine-induced E-selectin expression cycle. We found that distamycin prolonged E-selectin expression, both by sustaining mRNA transcription and by extending the transcript's half-life. The distamycin effect on transcription was mediated through one of the three NF-kappaB-HMG-I(Y) binding sites (NF-kappaBII) within the promoter. This suggests that the NF-kappaB-HMG-I(Y) complex interacting at the NF-kappaBII site plays a role not only in cytokine induction of E-selectin expression, but also in its down-modulation.

Characterization of leukotriene production in vivo and in vitro in resident and elicited peritoneal macrophages in chickens and mice

Previously, we reported differences in arachidonic acid metabolism in elicited chicken peritoneal macrophages when compared with murine resident and elicited peritoneal macrophages. We now describe leukotriene (LT) production in the same systems, using resident (murine) and inflammatory macrophages (from both species). Inflammatory (4- or 42-g Sephadex-elicited) peritoneal macrophages from chickens lacked the capacity to produce LT in vivo (following opsonized zymosan [OZ] stimulation) or in vitro, in response to A23187. In addition, chicken macrophages were unable to metabolize exogenously added LTC4 or LTD4 in vitro. In contrast, resident murine peritoneal macrophages produced measurable quantities of LTs (in vivo) within 5 min with an 8-fold increase after 45 min. LTC4 was effectively converted to LTE4 in vivo in a time-dependent manner (65% LTC4/35% LTE4 after 5 min stimulation with OZ and 6% LTC4/94% LTE4 after 60 min stimulation), but no in vitro. The lack of LTC4 metabolism to LTE4 in vitro could not be explained by cell-cell interaction between adherent and nonadherent cells. LTD4 was not detected under any experimental condition. Murine peritoneal cells incubated with LTD4 (with or without agonist) produced LTE4 in a time-dependent fashion. Addition of L-cysteine (a dipeptidase inhibitor) did not explain the lack of detectable levels of LTD4 following intraperitoneal stimulation with OZ. These results suggest that elicited chicken peritoneal macrophages are incapable of producing LTs compared to murine peritoneal macrophages. In addition, these studies fail to explain the different product profiles with in vivo stimulation of murine peritoneal macrophages as compared to in vitro stimulation.

Characterization of the import pathway of the F(A)d subunit of mitochondrial ATP synthase into isolated plant mitochondria

The synthetic precursor of the F(A)d subunit of mitochondrial ATP synthase was imported into isolated soybean cotyledon mitochondria. Import of the F(A)d precursor was accompanied by processing to a lower molecular weight mature form. The F(A)d precursor displayed the following import characteristics not seen before with plant mitochondria: efficient import in the absence of external ATP and import of wheat germ-translated precursor. Pretreatment of the F(A)d precursor with NEM did not inhibit import. Taken together with the lack of a requirement for external ATP, this indicates that this precursor does not require extramitochondrial ATP-dependent factors for import. Binding studies indicated that the F(A)d precursor bound to a proteinaceous component of the mitochondrial outer membrane. Inhibitor studies indicated that processing was most likely via the general mitochondrial processing peptidase. The results suggest that import of this subunit occurs via a pathway different from the general import pathway described for the majority of precursor proteins.

Role of image-guided core-needle biopsy in the management of patients with lymphoma

PURPOSE

The results of 106 radiologically guided core needle biopsies in 96 patients were analyzed retrospectively to evaluate the accuracy, safety, and role of this technique in the management of patients with lymphoma and to determine factors predictive of success.

PATIENTS AND METHODS

Biopsies were performed in 51 patients with low-grade non-Hodgkin's lymphoma (NHL), 24 with high-grade NHL, 16 with previously diagnosed Hodgkin's disease (HD), and 15 with no previous history of lymphoma. Disease was infradiaphragmatic in 92 patients and supradiaphragmatic in 14. Computed tomography (CT) guidance was used in 98 biopsies and ultrasonography (US) in eight.

RESULTS

The biopsy was diagnostic and yielded information on the basis of which treatment was started in 88 of 106 patients. The procedure was well tolerated and there were no major complications. Small size of the sample or inappropriate tissue sampled were the main causes of failure. The technique was equally successful in the diagnosis of HD and both high-grade and low-grade NHL as in nonlymphoproliferative disorders. The procedure was equally successful at diagnosis as at suspected recurrence or progression. In 33 of 80 cases in which the biopsy was performed at the time of recurrence or progression, the histology had changed; in 31 of 33, this influenced treatment. The technique was efficient at diagnosing transformation of follicular NHL in 16 of 18 patients, which allowed early adjustment of treatment at recurrence.

CONCLUSION

At St Bartholomew's Hospital (SBH), image-guided core-needle biopsy has proven to be a quick, safe, and efficient alternative to excisional biopsy in the evaluation of lymphoproliferative disorders at presentation, recurrence, or progression. It should become the procedure of choice for histologic sampling in the absence of peripheral lymphadenopathy.

Cloning, analysis and inactivation of the ndhK gene encoding a subunit of NADH quinone oxidoreductase from Anabaena PCC 7120

The function of the type-1 pyridine nucleotide dehydrogenase (NDH-1) in the cyanobacterium Anabaena PCC 7120 was investigated. Immunological analysis with antibodies raised against NdhK from Synechocystis PCC 6803, a subunit of NDH-1, showed that NdhK in Anabaena PCC 7120 is only present on the plasma membrane, which confirms the results of previous studies [Howitt, C.A., Smith, G.D. & Day, D. A. (1993) Biochim. Biophys. Acta 114], 313-320]. Southern analysis with probes from the operon encoding ndhC-K-J from Synechocystis PCC 6803 showed that this operon is also conserved in Anabaena PCC 7120. Part of the operon was amplified using PCR with degenerate primers designed against two sequences encoding regions of NdhC and NdhJ that are conserved between cyanobacteria and chloroplasts. The nucleotide sequence of ndhK encodes a protein of 245 amino acids with a predicted molecular mass of 27.5 kDa. The coding regions of ndhC and ndhK overlap by 7 bp, as found in the chloroplasts of liverwort, maize, and rice. This is markedly different from the case in Synechocystis PCC 6803 where a 71-bp non-coding, intergenic spacer region lies between ndhC and ndhK. The ndhK clone was interrupted by the insertion of a kanamycin-resistance gene and used to transform Anabaena PCC 7120.20 unsegregated transformants were produced, all of which died during attempts to segregate them. This indicates that under the selection conditions used, ndhK is an essential gene in Anabaena PCC 7120.

Adipose tissue stearoyl-CoA desaturase mRNA is increased by obesity and decreased by polyunsaturated fatty acids

Stearoyl-CoA desaturase (SCD) is a key regulatory enzyme in the synthesis of unsaturated fatty acids. Although regulation of hepatic SCD by obesity and polyunsaturated fatty acids (PUFA) has been well investigated, no studies have addressed whether similar regulation occurs in adipose tissue. We addressed these questions by feeding control (12% corn oil) and high-PUFA (48% corn oil) diets to lean and obese Zucker rats and analyzing SCD mRNA levels in adipose tissue and liver. We report that SCD mRNA content was dramatically elevated in adipose tissue of obese vs. lean rats on both diets and was significantly decreased by PUFA in both genotypes. Interestingly, we demonstrate that SCD expression was directly downregulated in a dose dependent manner by PUFA in 3T3-L1 adipocytes. We conclude that 1) obese Zucker rats overexpress the SCD gene in both liver and adipose tissue and 2) PUFA directly suppress SCD expression in adipocytes. Further studies will elucidate the mechanisms responsible for obesity- and PUFA-mediated regulation of SCD in adipose cells.

Evidence for a link between translocation and processing during protein import into soybean mitochondria

The effect of metal chelators on protein import was investigated using isolated soybean mitochondria and soybean precursor proteins. Adding 1,10-phenanthroline, a metal chelator that can cross both mitochondrial membranes abolished import of both the alternative oxidase, and the F(A)d subunit of the ATP synthase, a matrix located protein. Other metal chelators such as EDTA, 1,7-phenanthroline and 4,7-phenanthroline, which cannot cross the mitochondrial membranes, had no effect on import. When processing, a known metal-dependent step inside mitochondria, was inhibited using a mutagenesis approach (changing a -2 arginine to a -2 glycine in the pre-piece of the precursor), so was import. Thus it would appear that in soybean, at least, translocation of proteins across the mitochondrial membrane, as well as processing, relies on a metal dependent step. Taken together, the data suggest the two processes may be directly connected in these mitochondria.

Antagonistic effects of dietary arachidonic acid and n-3 polyunsaturated fatty acids

Arachidonic acid (AA) is a polyunsaturated fatty acid (PUFA) found exclusively in animal products and is one of the most important fatty acids associated with membrane phospholipids. When liberated from membrane phospholipids, AA can be oxidized to a variety of eicosanoids, compounds important in cell-cell signaling. Dietary n-3 PUFA have been effectively used to attenuate tissue AA levels and subsequent eicosanoid formation. However, only recently have the effects of dietary AA been investigated. This review discusses the antagonistic effects of dietary AA and n-3 PUFA, eicosanoid formation and the evidence suggesting divergent effects with regard to circulating triglycerides, beta-oxidation and tumor necrosis factor.

Biological effects of dietary arachidonic acid. Introduction

The intent of this symposium is to assemble current knowledge of the role of arachidonic acid (AA) in the diet to provide a conceptual and mechanistic framework for future research. The principal focus is on the varied biological effects of dietary AA, including opposing effects of n-3 and n-6 polyunsaturated fatty acids (PUFA); regulation of n-6 PUFA metabolism, eicosanoid synthesis and gene expression; the importance of AA in infant nutrition and the contemporary Western diet in general; and the effects of AA on tumor promotion. Through its myriad actions and remarkably ubiquitous presence in cells, AA can be argued to affect every cell of the body. Although the varied molecular events associated with the metabolism of AA have been subjects of intense investigation, the ability of AA in the diet to alter AA levels in cellular membranes is poorly described and is thus the focus of this symposium.

Generation of estrogen receptor mutants with altered ligand specificity for use in establishing a regulatable gene expression system

Considerable interest exists in developing an artificial system for the control of gene expression, based on the hormone binding domain (HBD) of steroid receptors. In this study we describe a yeast based approach which allows the identification of mutations within the HBD of steroid receptors, in this case the estrogen receptor, which result in altered specificity of the HBD with respect to its activation by ligands. Using this approach in yeast, we identified an estrogen receptor (HBD) mutant (His524 to Gln) whose activation by 17 beta-estradiol (E2) is significantly reduced while activation by a diphenol indene-ol compound (GR132706X) is increased, compared to the wild type estrogen receptor. When the activity of the mutant receptor was tested in mammalian cells the altered specificity was maintained. A chimeric transcription factor was constructed, in which the mutated estrogen receptor HBD was linked to the DNA binding domain of GAL4 and an 11 amino acid transcriptional activation domain of RelA. Reporter gene activation by this chimera was decreased in response to E2 and increased in response to GR132706X, as compared to the corresponding chimeric transcription factor containing the wild type estrogen receptor HBD. This approach should allow the development of a steroid receptor HBD based regulator of gene expression, whose activity is controlled specifically by a synthetic ligand, that would not affect the activity of endogenous steroid receptors.

Selectin synthesis and inflammation

The selectins are a family of three cell-surface-presented glycoprotein receptors. They play a key role in the initial adhesive interaction between leukocytes and endothelial cells at sites of inflammation. The presence of selectins on the cell surface is tightly regulated and inappropriate appearance is associated with a number of inflammatory disease conditions.

Low grade gastric B-cell lymphoma of mucosa associated lymphoid tissue in immunocompromised patients

An increased incidence of non-Hodgkin's lymphoma is seen in patients with immunodeficiency from any cause. The majority of these are high grade B-cell lymphoma and most are associated with the Epstein-Barr virus (EBV). In post-transplant lymphoma/lymphoproliferative disorders the tumour may regress following reduction of immuno-suppression but in AIDS the lymphomas show a characteristic aggressive course and poor prognosis. We describe low grade B-cell gastric lymphoma of mucosa associated lymphoid tissue (MALT) in three immunocompromised patients (two post-transplant, one HIV positive). In each case, the tumour showed classical morphological features of gastric MALT lymphoma and was not associated with EBV. Helicobacter pylori was identified in each case. Clinical follow-up suggests that the behaviour in these tumours is similar to that seen in MALT lymphomas in immunocompetent patients and not typical of the lymphomas usually associated with immunosuppression. Although the finding of MALT lymphoma in immunosuppressed patients might be coincidental, the association of some MALT lymphomas with autoimmune disease suggests that dysregulation of the immune system might play a role in the pathogenesis of these tumours.

The alternative oxidase is encoded in a multigene family in soybean

The copy number of the alternative oxidase gene, Aox, was investigated in soybean (Glycine max L.) using a Polymerase chain reaction (PCR) approach to amplify fragments from soybean genomic DNA. The primers used were based on absolutely conserved regions of Aox cDNA clones from a variety of plant species and the yeast Hansenula anomala. After subcloning of the 170-bp PCR products, 12 individual colonies were sequenced. Eleven plasmids yielded inserts representing three sequences in the ratio 4:3:4 (Aox1-3). The sequence of Aox1 was 100% identical at the nucleic acid level to the published full-length cDNA from soybean. The other two sequences were 60-75% identical to Aox1 and to each other at the nucleic acid and protein levels. Similar analysis of Nicotiana tabacum L. revealed an additional gene copy with high homology to the soybean Aox2 sequence. Genomic DNA from soybean cut with Hind III and probed with the full-length Aox1 yielded a single positive band of 6.5 kb; when the same genomic blot was probed with a mixture of all three PCR fragments, three bands of 9 kb, 6.5 kb and 3 kb were detected. Reverse transcription-PCR performed on total RNA from various soybean tissues, followed by hybridisation with the three Aox sequences individually, revealed differential expression of the Aox genes between cotyledons and leaves. It is suggested that soybean contains a multigene Aox family. The implication of this for the understanding of alternative oxidase expression and regulation in plant tissues is discussed.