Repeated, recent and diverse transfers of a mitochondrial gene to the nucleus in flowering plants

A central component of the endosymbiotic theory for the bacterial origin of the mitochondrion is that many of its genes were transferred to the nucleus. Most of this transfer occurred early in mitochondrial evolution; functional transfer of mitochondrial genes has ceased in animals. Although mitochondrial gene transfer continues to occur in plants, no comprehensive study of the frequency and timing of transfers during plant evolution has been conducted. Here we report frequent loss (26 times) and transfer to the nucleus of the mitochondrial gene rps10 among 277 diverse angiosperms. Characterization of nuclear rps10 genes from 16 out of 26 loss lineages implies that many independent, RNA-mediated rps10 transfers occurred during recent angiosperm evolution; each of the genes may represent a separate functional gene transfer. Thus, rps10 has been transferred to the nucleus at a surprisingly high rate during angiosperm evolution. The structures of several nuclear rps10 genes reveal diverse mechanisms by which transferred genes become activated, including parasitism of pre-existing nuclear genes for mitochondrial or cytoplasmic proteins, and activation without gain of a mitochondrial targeting sequence.

Malignant round cell tumours of bone: atypical clinical and imaging features

OBJECTIVE

To describe the clinical, radiological and MRI features of six atypical cases of histologically proven appendicular Ewing sarcoma/primitive neuroectodermal tumour (PNET).

DESIGN

Retrospective review of case notes and available imaging was carried out.

PATIENTS

Six patients (4 male, 2 female; mean age 27 years, range 19-44 years), presenting over a 77-month period, were identified from the Bone Tumour Register. All had unusual clinical and imaging features for Ewing sarcoma/PNET.

RESULTS AND CONCLUSIONS

Four tumours were centred on the distal femoral metaphysis, one in the proximal tibial metaphysis and one in the distal tibial metaphysis. Plain radiographs were available in four cases and showed minor cortical changes. MRI demonstrated a relatively small, eccentrically located intraosseous component with a large, eccentric extraosseous component. Extension into the epiphysis was seen in three cases and into the adjacent joint in two cases. Intraosseous "skip" metastases were present in three cases. The clinical and imaging features were atypical for conventional intraosseous Ewing sarcoma/PNET and the exact site of origin (intraosseous, periosteal or soft-tissue) was unclear.

Highly unsaturated (n-3) fatty acids, but not alpha-linolenic, conjugated linoleic or gamma-linolenic acids, reduce tumorigenesis in Apc(Min/+) mice

We showed previously that dietary eicosapentaenoic acid [EPA, 20:5(n-3)] is antitumorigenic in the APC:(Min/+) mouse, a genetic model of intestinal tumorigenesis. Only a few studies have evaluated the effects of dietary fatty acids, including EPA and docosahexaenoic acid [DHA, 22:6(n-3)], in this animal model and none have evaluated the previously touted antitumorigenicity of alpha-linolenic acid [ALA, 18:3(n-3)], conjugated linoleic acid [CLA, 77% 18:2(n-7)], or gamma-linolenic acid [GLA, 18:3(n-6)]. Stearidonic acid [SDA, 18:4(n-3)], the Delta6-desaturase product of ALA, which is readily metabolized to EPA, has not been evaluated previously for antitumorigenic efficacy. This study was undertaken to evaluate the antitumorigenicity of these dietary fatty acids (ALA, SDA, EPA, DHA, CLA and GLA) compared with oleic acid [OA, 18:1(n-9)] at a level of 3 g/100 g in the diets of APC:(Min/+) mice and to determine whether any alterations in tumorigenesis correspond to alterations in prostaglandin biosynthesis. Tumor multiplicity was significantly lower by approximately 50% in mice fed SDA or EPA compared with controls, whereas less pronounced effects were observed in mice fed DHA (P: = 0.15). ALA, CLA and GLA were ineffective at the dose tested. Although lower tumor numbers coincided with significantly lower prostaglandin levels in SDA- and EPA-fed mice, ALA and DHA supplementation resulted in equally low prostaglandin levels, despite proving less efficacious with regard to tumor number. Prostaglandin levels did not differ significantly in the CLA and GLA groups compared with controls. These results suggest that SDA and EPA attenuate tumorigenesis in this model and that this effect may be related in part to alterations in prostaglandin biosynthesis.

Antagonism of arachidonic acid is linked to the antitumorigenic effect of dietary eicosapentaenoic acid in Apc(Min/+) mice

The multiple intestinal neoplasia (Apc(Min/+)) mouse possesses a germline mutation at codon 850 of the adenomatous polyposis coli (Apc) gene resulting in the formation of a nonfunctional truncated gene product. Following a somatic mutation of the remaining wild-type allele, mice spontaneously develop approximately 40-50 tumors throughout the intestinal tract. This mouse model has been used to study intestinal tumorigenesis because this mutation is analogous to the inherited APC mutation in humans with familial adenomatous polyposis (FAP). These individuals characteristically develop numerous adenomas throughout their intestinal tracts. Only a few studies have evaluated the effects of dietary fatty acids on tumorigenesis in this animal model with varying results, and none have linked these effects to alterations in arachidonic acid (AA) metabolism. This study was designed to evaluate the antitumorigenic effect of dietary (n-3) polyunsaturated fatty acids (PUFA) in the Apc(Min/+) mouse model and to determine whether these effects are related to inhibition of AA metabolism. Male Apc(Min/+)mice were fed diets supplemented with eicosapentaenoic acid (EPA), AA or a combination of AA + EPA. Mean tumor number in the EPA group was 68% lower (P<0.05) compared with the control group, whereas AA supplementation did not significantly alter tumor load. The reduction in tumor load coincided with significant reductions in intestinal AA content and levels of prostaglandins. However, supplementing AA to the EPA diet (AA + EPA) abolished the antitumorigenic effect of EPA, increased tissue AA content fourfold and prostaglandin production two- to fourfold. These results indicate that AA is involved in tumorigenesis and suggest that EPA's ability to reduce tumor load in Apc(Min/+) mice is related to reductions in tissue AA content or its metabolism.

Discordant effect of aspirin and indomethacin on intestinal tumor burden in Apc(Min/+)mice

Epidemiologic and animal studies indicate that sustained use of non-steroidal anti-inflammatory drugs (NSAIDs) have a chemopreventive effect against the incidence of colorectal neoplasia and subsequent mortality. We previously demonstrated that sulindac significantly reduces intestinal tumor load in Apc(Min/+)mice and the tumor regression was not necessarily correlated with prostaglandin biosynthesis. In the present study, we further investigate the relationship of NSAID treatment and tumorigenesis in the Apc(Min/+)mouse model. We demonstrate that indomethacin (9 ppm) is a very potent chemopreventive agent, reducing tumor load by 85% and significantly inhibiting basal and ex vivo prostaglandin formation (P< 0.006 and P< 0.0001, respectively). Aspirin (400 ppm) has a similar impact on reducing prostaglandin levels, but in contrast to indomethacin, is uneffective in reducing the tumor load. The data indicate a discordance between the impact of different NSAIDs on tumorigenesis in Apc(Min/+)mice.

Import of precursor proteins into mitochondria from soybean tissues during development

Characterisation of the amount of protein import of the alternative oxidase (AOX) and the F(A)d precursor proteins (previously shown to use different import pathways) into mitochondria from developing soybean tissues indicated that they displayed different patterns. Import of the AOX declined in both cotyledon and root mitochondria with increasing age, whereas the import of the F(A)d into cotyledon mitochondria remained high throughout the same period. Using primary leaf mitochondria, it was evident that import of AOX remained high while it declined in cotyledon and root mitochondria. The amount of import of the AOX into mitochondria from different tissues closely matched the amount of the Tom 20 receptor.

Neoadjuvant chemotherapy with doxorubicin and cisplatin in malignant fibrous histiocytoma of bone: A European Osteosarcoma Intergroup study

PURPOSE

Studies involving small case series have suggested that malignant fibrous histiocytoma of bone (MFH-B) is a chemosensitive tumor and that chemotherapy may improve survival. In this study, we evaluated clinical and pathologic response rates and survival in a series of patients treated with a consistent chemotherapy regimen of doxorubicin and cisplatin (DOX/DDP).

PATIENTS AND METHODS

Study patients were required to have biopsy-proven MFH-B, no previous chemotherapy, and primary or metastatic measurable disease and to be </= 65 years of age. Treatment consisted of doxorubicin 25 mg/m(2)/d days 1 through 3 and cisplatin 100 mg/m(2) by 4-hour intravenous infusion every 3 weeks for six cycles. In patients with operable primary tumors, chemotherapy was planned to start within 42 days of biopsy, with definitive surgery performed after three cycles.

RESULTS

Forty-one patients had operable nonmetastatic limb sarcomas, and 23 (56%) completed six chemotherapy cycles. Limb salvage was possible in 33 patients (80%), and 16 (42%) of 38 assessable specimens showed a good pathologic response (>/= 90% necrosis). Median time to progression was 56 months, and the 5-year progression-free survival rate was 56% (95% confidence interval [CI], 40% to 72%). Median survival time was 63 months, and the 5-year survival rate was 59% (95% CI, 41% to 77%). Patients with a good pathologic response had longer survival times and times to progression than did those with a poor response. Also treated were two patients with locally recurrent and nine with metastatic disease, and these patients had a median survival time of 17.5 months.

CONCLUSION

Our study suggests that adjuvant or neoadjuvant chemotherapy with DOX/DDP is beneficial in MFH-B. Good pathologic response rates and survivals are quite comparable with those for osteosarcoma, a related bone tumor for which adjuvant or neoadjuvant chemotherapy is an accepted practice.

Decreased activity of the L-arginine-nitric oxide metabolic pathway in patients with congestive heart failure

BACKGROUND

Impaired endothelium-dependent, nitric oxide (NO)-mediated vasodilation may contribute to increased vasomotor tone in patients with heart failure. Whether decreased endothelium-dependent, NO-mediated vasodilation in patients with heart failure is due to decreased synthesis or increased degradation of NO is unknown.

METHODS AND RESULTS

To specifically assess the synthetic activity of the L-arginine-NO metabolic pathway, urinary excretion of [15N]nitrates and [15N]urea was determined after a primed continuous intravenous infusion of L-[15N]arginine (40 micromol/kg) in 16 patients with congestive heart failure and 9 age-matched normal control subjects at rest and during submaximal treadmill exercise. After infusion of L-[15N]arginine, 24-hour urinary excretion of [15N]nitrates was decreased in patients with congestive heart failure at rest (2.2+/-0.5 versus 8.0+/-2.3 micromol/24 h) and during submaximal exercise (2.4+/-1.2 versus 11. 4+/-4.0 micromol/24 h) compared with control subjects (both P<0.01). After infusion of L-[15N]arginine, 24-hour urinary excretions of [15N]urea at rest in patients with congestive heart failure and control subjects were not different (1.1+/-0.3 versus 1.2+/-0.2 mmol/24 h, P>0.20).

CONCLUSIONS

A specific decrease in synthetic activity of the L-arginine-NO metabolic pathway contributes to decreased endothelium-dependent vasodilation in patients with congestive heart failure.

Dermatological conditions and HIV disease

An update on skin conditions which can affect patients with human immunodeficiency virus.

Relationship of beta-catenin and Bcl-2 expression to sulindac-induced regression of intestinal tumors in Min mice

Non-steroidal anti-inflammatory drugs (NSAIDs) can cause regression of early intestinal tumors and although this is believed to involve cyclooxygenase-2 and apoptosis, the molecular mechanisms remain unclear. Cytoplasmic and nuclear beta-catenin are overexpressed in many of these lesions and Bcl-2, which inhibits apoptosis, may also be elevated during the course of intestinal tumorigenesis. We recently showed that sulindac causes regression of 70-80% of small intestinal tumors in Min/+ mice within 4 days, but does not have the same impact on colonic lesions; after 20 days of treatment the tumor load stabilizes at 10-20% of that in untreated animals. The aim of this study was to determine if NSAID-induced regression of intestinal adenomas might be associated with changes in beta-catenin or Bcl-2 expression. Intestinal tumors from Min/+ mice were harvested after treatment with sulindac for 2, 4 or 20 days and evaluated for expression of beta-catenin and Bcl-2 using immunohistochemistry. There was a > or = 50% decrease in beta-catenin (P = 0.001) and diminishing Bcl-2 (P = 0.019) in small intestinal tumors harvested between 2 and 4 days of treatment when compared with untreated controls. In contrast, small intestinal tumors from animals treated for 20 days were not significantly different from untreated controls. Colonic tumors expressed higher levels of Bcl-2 than those from the small intestine and did not show any significant changes in either Bcl-2 or beta-catenin expression after treatment. Results suggest that modulation of aberrant beta-catenin expression occurs during NSAID-induced regression of intestinal adenomas and that Bcl-2 may confer resistance to these effects.

Measurement of DNA cross-linking in patients on ifosfamide therapy using the single cell gel electrophoresis (comet) assay

The single cell gel electrophoresis comet assay has become established as a sensitive technique for measuring DNA strand breaks. The technique has been modified to allow the sensitive detection and quantitation of DNA interstrand cross-linking at the single cell level. Cells are irradiated immediately before analysis to deliver a fixed level of random strand breakage. After embedding of cells in agarose and lysis, the presence of cross-links retards the electrophoretic mobility of the alkaline denatured cellular DNA. Cross-links are, therefore, quantitated as the decrease in the comet tail moment compared with irradiated controls. Using this method, a linear response of cross-linking versus dose of chlorambucil over a wide dose range was demonstrated in human lymphocytes after drug treatment ex vivo. The method was also sensitive enough to determine cross-linking in clinical samples after chemotherapy. For example, crosslinking was observed in the lymphocytes of patients receiving ifosfamide (3 g/m2/day) as a continuous infusion for 3-5 days or as a 3-h infusion daily for 3 days. Cross-links were detected in all patients within 3 h, with no evidence of DNA single strand break formation. In patients receiving continuous infusion, a plateau of cross-linking was reached by 24 h. In the patients receiving ifosfamide over 3 h, a clear decrease in the peak level of cross-linking was observed before subsequent infusions.

Colorectal cancer in adolescents

Colorectal cancer, one of the most common malignancies among adults, is rare in adolescence. This low incidence coupled with non-specific symptoms and aggressive natural history leads to a poorer prognosis than in reported adult series. This article describes two cases of colorectal cancer in adolescents and reviews the literature regarding this rare condition. Earlier diagnosis and a greater understanding of the natural history may lead to improved treatment with concomitant improvements in survival.

Single-step method for the determination of the amount of the common deletion in mitochondrial DNA

A fluorescent-based quantitative PCR assay to measure the percentage of the common deletion in rat mitochondria is reported. The amount of the common deletion is measured relative to the amount of total mitochondrial (mt)DNA. The use of a heterologous competitor construct allows the reaction to be monitored to ensure that exponential accumulation of products occurs. The use of fluorescence-labeled primers provides a safe and sensitive means to quantify products without any adjustment for size. This assay will allow the quantitative determination of the common deletion with one dilution range.

Signals required for the import and processing of the alternative oxidase into mitochondria

The critical residues involved in targeting and processing of the soybean alternative oxidase to plant and animal mitochondria was investigated. Import of various site-directed mutants into soybean mitochondria indicated that positive residues throughout the length of the presequence were important for import, not just those in the predicted region of amphiphilicity. The position of the positive residues in the C-terminal end of the presequence was also important for import. Processing assays of the various constructs with purified spinach mitochondrial processing peptidase showed that all the -2-position mutants had a drastic effect on processing. In contrast to the import assay, the position of the positive residue could be changed for processing. Deletion mutants confirmed the site-directed mutagenesis data in that an amphiphilic alpha-helix was not the only determinant of mitochondrial import in this homologous plant system. Import of these constructs into rat liver mitochondria indicated that the degree of inhibition differed and that the predicted region of amphiphilic alpha-helix was more important with rat liver mitochondria. Processing with a rat liver matrix fraction showed little inhibition. These results are discussed with respect to targeting specificity in plant cells and highlight the need to carry out homologous studies and define the targeting requirements to plant mitochondria.

Assessment of the arachidonic acid content in foods commonly consumed in the American diet

Arachidonic acid (AA) is an extremely important fatty acid involved in cell regulation. When provided in the diet, it is cogently incorporated in membrane phospholipids and enhances eicosanoid biosynthesis in vivo and in vitro; however, controversy exists as to the levels of AA in food and in the diet. This study determined the amount of AA in cooked and raw portions of beef (rib eye), chicken (breast and thigh), eggs, pork (loin), turkey (breast), and tuna; it compared these results to values published in Agriculture Handbook No. 8 (HB-8). The cooked portions were prepared as described in HB-8. With the exception of chicken thigh and tuna, the levels of AA (w/w) in the selected foods analyzed were significantly higher, in general, than those values published in HB-8. The greatest differences were observed in beef (raw and cooked), turkey breast (raw and cooked), and pork (cooked) where AA levels were twice that of the values in HB-8. In contrast, the AA and n-3 fatty acid contents in tuna were almost half the HB-8 values. The present data indicate that HB-8 tends to underreport the amounts of AA in a number of foods commonly consumed in the American diet, and new initiatives should be considered to validate and update the current database for fatty acid composition of foods.

Differential expression of alternative oxidase genes in soybean cotyledons during postgerminative development

The expression of the alternative oxidase (AOX) was investigated during cotyledon development in soybean (Glycine max [L.] Merr.) seedlings. The total amount of AOX protein increased throughout development, not just in earlier stages as previously thought, and was correlated with the increase in capacity of the alternative pathway. Each AOX isoform (AOX1, AOX2, and AOX3) showed a different developmental trend in mRNA abundance, such that the increase in AOX protein and capacity appears to involve a shift in gene expression from AOX2 to AOX3. As the cotyledons aged, the size of the mitochondrial ubiquinone pool decreased. We discuss how this and other factors may affect the alternative pathway activity that results from the developmental regulation of AOX expression.

Identification of a novel stress activated kinase in kidney and heart

We have previously described the patterns of stress kinase activation in rat kidney and heart in response to ischemia/reperfusion (Yin et al., 1997, J. Biol. Chem. 272, 19943-19950). During the course of these studies, we observed the activation of a novel kinase capable of phosphorylating c-Jun on serines 63 and 73. The molecular weight of this kinase is approximately 37 kD, significantly below the molecular weight of all previously identified Jun N-terminal kinase (JNK) isoforms. The pattern of activation of this 37 kD kinase in response to ischemia/reperfusion in both kidney and heart is distinct from that of known JNK isoforms. Western analysis of human renal proximal tubular epithelial (RPTE) cells, using a non-isoform specific phospho-JNK antibody, revealed the phosphorylation (activation) of a 37 kD protein in response to hypoxia. The 37 kD protein in RPTE cells is phosphorylated by other stress stimuli capable of activating JNK. Western analysis of tissues, using a non-isoform specific JNK antibody, identifies a cross-reactive 37 kD protein expressed in the liver, thymus and lymph node which is likely to correspond to the 37 kDa stress-activated kinase. The results of this study have led to the identification of a potentially novel kinase closely related to JNK but showing a distinct pattern of activation.

Mitochondrial protein import in plants. Signals, sorting, targeting, processing and regulation

Mitochondrial biogenesis requires a coordinated expression of both the nuclear and the organellar genomes and specific intracellular protein trafficking, processing and assembly machinery. Most mitochondrial proteins are synthesised as precursor proteins containing an N-terminal extension which functions as a targeting signal, which is proteolytically cleaved off after import into mitochondria. We review our present knowledge on components and mechanisms involved in the mitochondrial protein import process in plants. This encompasses properties of targeting peptides, sorting of precursor proteins between mitochondria and chloroplasts, signal recognition, mechanism of translocation across the mitochondrial membranes and the role of cytosolic and organellar molecular chaperones in this process. The mitochondrial protein processing in plants is catalysed by the mitochondrial processing peptidase (MPP), which in contrast to other sources, is integrated into the bc1 complex of the respiratory chain. This is the most studied component of the plant import machinery characterised to date. What are the biochemical consequences of the integration of the MPP into an oligomeric protein complex and how are several hundred presequences of precursor proteins with no sequence similarities and no consensus for cleavage, specifically cleaved off by MPP? Finally we will address the emerging area of the control of protein import into mitochondria.