BRCA1 deficiency enhances the aggressiveness of breast cancer cells expressing HPV16 oncoproteins

BACKGROUND INFORMATION

The precise etiology of breast cancer is not completely understood, although women with BRCA1 gene mutations have a significantly increased risk of developing the disease. In addition, sporadic breast cancer is frequently associated with decreased BRCA1 gene expression. Growing evidence of Human papillomaviruses (HPVs) infections in breast tumors has raised the possibility of the involvement of HPVs in the pathogenesis of breast cancer. We investigated whether the effects of HPV oncoproteins E6 and E7 were influenced by the expression levels of BRCA1. HPV16E6E7 (prototype or E6D25E/E7N29S Asian variant type) were stably expressed in MDA-MB231 breast cancer cells, wild type for BRCA1, or with BRCA1 knocked down.

RESULTS

Expression of HPV16E6E7 oncogenes did not affect BRCA1 levels and the abundance of HPV16E6E7 was not altered by BRCA1 knockdown. BRCA1 levels did not alter HPV16E6E7-dependent degradation of G1-S cell cycle proteins p53 and pRb. However, we found that the expression of G2-M cell cycle protein cyclin B1 enhanced by HPV16E6E7 was impacted by BRCA1 levels. Especially, we found the correlation between BRCA1 and cyclin B1 expression and this was also confirmed in breast cancer samples from a Thai cohort. We further demonstrated that the combination of HPV oncoproteins and low levels of BRCA1 protein appears to enhance proliferation and invasion. Transactivation activities of HPV16E6E7 on genes regulating cell proliferation and invasion (TGF-β and vimentin) were significantly increased in BRCA1-deficient cells.

CONCLUSIONS

Our results indicate that a deficiency of BRCA1 promotes the transactivation activity of HPV16E6E7 leading to increase of cell proliferation and invasion.

SIGNIFICANCE

HPV infection appears to have the potential to enhance the aggressiveness of breast cancers, especially those deficient in BRCA1.

Novel LIAS variants in a patient with epilepsy and profound developmental disabilities

Multiple mitochondrial enzymes employ lipoic acid as a coenzyme. Pathogenic variants in LIAS, encoding lipoic acid synthase (LIAS), are associated with autosomal recessive LIAS-related disorder (OMIM# 614462). This disorder is characterized by infantile-onset hypotonia, profound psychomotor delay, epileptic encephalopathy, nonketotic hyperglycinemia, and lactic acidosis. We present the case of a 20-year-old female who experienced developmental deficits at the age of 6 months and began to have seizures at 3 years of age. Exome sequencing revealed compound heterozygous novel variants in LIAS, designated c.277delC (p.Leu93Ter) and c.542A > T (p.Asp181Val). The p.Leu93Ter variant is predicted to cause loss of function due to the severe truncation of the encoded protein. To examine the p.Asp181Val variant, functional analysis was performed using Baker's yeast (Saccharomyces cerevisiae) lacking LIP5, the homologue of human LIAS. Wild-type LIAS promoted oxidative growth of the lip5∆ yeast strain. In contrast, lip5∆ yeast expressing p.Asp181Val exhibited poor growth, similar to known pathogenic variants, p.Asp215Glu and p.Met310Thr. Our work has expanded the phenotypic and genotypic spectrum of LIAS-related disorder and established the use of the yeast model as a system for functional study of novel missense variants in LIAS.

Mitochondrial dysfunction from malathion and chlorpyrifos exposure is associated with degeneration of GABAergic neurons in Caenorhabditis elegans

Toxicity resulting from off-target effects, beyond acetylcholine esterase inhibition, for the commonly used organophosphate (OP) insecticides chlorpyrifos (CPS) and malathion (MA) was investigated using Saccharomyces cerevisiae and Caenorhabditis elegans model systems. Mitochondrial damage and dysfunction were observed in yeast following exposure to CPS and MA, suggesting this organelle is a major target. In the C. elegans model, the mitochondrial unfolded protein response pathway showed the most robust induction from CPS and MA treatment among stress responses examined. GABAergic neurodegeneration was observed with CPS and MA exposure. Impaired movement observed in C. elegans exposed to CPS and MA may be the result of motor neuron damage. Our analysis suggests that stress from CPS and MA results in mitochondrial dysfunction, with GABAergic neurons sensitized to these effects. These findings may aid in the understanding of toxicity from CPS and MA from high concentration exposure leading to insecticide poisoning.

Baseline bone turnover marker levels can predict change in bone mineral density during antiresorptive treatment in osteoporotic patients: the Copenhagen bone turnover marker study

Anti-resorptive osteoporosis treatment might be more effective in patients with high bone turnover. In this registry study including clinical data, high pre-treatment bone turnover measured with biochemical markers was correlated with higher bone mineral density increases. Bone turnover markers may be useful tools to identify patients benefitting most from anti-resorptive treatment.

INTRODUCTION

In randomized, controlled trials of bisphosphonates, high pre-treatment levels of bone turnover markers (BTM) were associated with a larger increase in bone mineral density (BMD). The purpose of this study was to examine this correlation in a real-world setting.

METHODS

In this registry-based cohort study of osteoporosis patients (n = 158) receiving antiresorptive therapy, the association between pre-treatment levels of plasma C-telopeptide of type I Collagen (CTX) and/or N-terminal propeptide of type I procollagen (PINP) and change in bone mineral density (BMD) at lumbar spine, total hip, and femoral neck upon treatment was examined. Patients were grouped according to their pre-treatment BTM levels, defined as values above and below the geometric mean for premenopausal women.

RESULTS

Pre-treatment CTX correlated with annual increase in total hip BMD, where patients with CTX above the geometric mean experienced a larger annual increase in BMD (p = 0.008) than patients with CTX below the geometric mean. The numerical pre-treatment level of CTX showed a similar correlation at all three skeletal sites (total hip (p = 0.03), femoral neck (p = 0.04), and lumbar spine (p = 0.0003)). A similar association was found for PINP where pre-treatment levels of PINP above the geometric mean correlated with a larger annual increase in BMD for total hip (p = 0.02) and lumbar spine (p = 0.006).

CONCLUSION

Measurement of pre-treatment BTM levels predicts osteoporosis patients' response to antiresorptive treatment. Patients with high pre-treatment levels of CTX and/or PINP benefit more from antiresorptive treatment with larger increases in BMD than patients with lower pre-treatment levels.

Chemical-Genetic Interactions of Bacopa monnieri Constituents in Cells Deficient for the DNA Repair Endonuclease RAD1 Appear Linked to Vacuolar Disruption

Colorectal cancer is a common cancer worldwide and reduced expression of the DNA repair endonuclease XPF (xeroderma pigmentosum complementation group F) is associated with colorectal cancer. Bacopa monnieri extracts were previously found to exhibit chemical-genetic synthetic lethal effects in a Saccharomyces cerevisiae model of colorectal cancer lacking Rad1p, a structural and functional homologue of human XPF. However, the mechanisms for B. monnieri extracts to limit proliferation and promote an apoptosis-like event in RAD1 deleted yeast was not elucidated. Our current analysis has revealed that B. monnieri extracts have the capacity to promote mutations in rad1∆ cells. In addition, the effects of B. monnieri extracts on rad1∆ yeast is linked to disruption of the vacuole, similar to the mammalian lysosome. The absence of RAD1 in yeast sensitizes cells to the effects of vacuole disruption and the release of proteases. The combined effect of increased DNA mutations and release of vacuolar contents appears to induce an apoptosis-like event that is dependent on the meta-caspase Yca1p. The toxicity of B. monnieri extracts is linked to sterol content, suggesting saponins may be involved in limiting the proliferation of yeast cells. Analysis of major constituents from B. monnieri identified a chemical-genetic interaction between bacopasaponin C and rad1∆ yeast. Bacopasaponin C may have potential as a drug candidate or serve as a model for the development of analogs for the treatment of colorectal cancer.

Novel SOX10 Mutations in Waardenburg Syndrome: Functional Characterization and Genotype-Phenotype Analysis

Waardenburg syndrome (WS) is a prevalent hearing loss syndrome, concomitant with focal skin pigmentation abnormalities, blue iris, and other abnormalities of neural crest-derived cells, including Hirschsprung’s disease. WS is clinically and genetically heterogeneous and it is classified into four major types WS type I, II, III, and IV (WS1, WS2, WS3, and WS4). WS1 and WS3 have the presence of dystopia canthorum, while WS3 also has upper limb anomalies. WS2 and WS4 do not have the dystopia canthorum, but the presence of Hirschsprung’s disease indicates WS4. There is a more severe subtype of WS4 with peripheral nerve and/or central nervous system involvement, namely peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, WS, and Hirschsprung’s disease or PCW/PCWH. We characterized the genetic defects underlying WS2, WS4, and the WS4-PCW/PCWH) using Sanger and whole-exome sequencing and cytogenomic microarray in seven patients from six unrelated families, including two with WS2 and five with WS4. We also performed multiple functional studies and analyzed genotype–phenotype correlations. The cohort included a relatively high frequency (80%) of individuals with neurological variants of WS4. Six novel SOX10 mutations were identified, including c.89C > A (p.Ser30^∗), c.207_8 delCG (p.Cys71Hisfs^∗62), c.479T > C (p.Leu160Pro), c.1379 delA (p.Tyr460Leufs^∗42), c.425G > C (p.Trp142Ser), and a 20-nucleotide insertion, c.1155_1174dupGCCCCACTATGGCTCAGCCT (p.Phe392Cysfs^∗117). All pathogenic variants were de novo. The results of reporter assays, western blotting, immunofluorescence, and molecular modeling supported the deleterious effects of the identified mutations and their correlations with phenotypic severity. The prediction of genotype–phenotype correlation and functional pathology, and dominant negative effect vs. haploinsufficiency in SOX10-related WS were influenced not only by site (first two vs. last coding exons) and type of mutation (missense vs. truncation/frameshift), but also by the protein expression level, molecular weight, and amino acid content of the altered protein. This in vitro analysis of SOX10 mutations thus provides a deeper understanding of the mechanisms resulting in specific WS subtypes and allows better prediction of the phenotypic manifestations, though it may not be always applicable to in vivo findings without further investigations.

Disruption in iron homeostasis and impaired activity of iron-sulfur cluster containing proteins in the yeast model of Shwachman-Diamond syndrome

BACKGROUND

Shwachman-Diamond syndrome (SDS) is a congenital disease that affects the bone marrow, skeletal system, and pancreas. The majority of patients with SDS have mutations in the SBDS gene, involved in ribosome biogenesis as well as other processes. A Saccharomyces cerevisiae model of SDS, lacking Sdo1p the yeast orthologue of SBDS, was utilized to better understand the molecular pathogenesis in the development of this disease.

RESULTS

Deletion of SDO1 resulted in a three-fold over-accumulation of intracellular iron. Phenotypes associated with impaired iron-sulfur (ISC) assembly, up-regulation of the high affinity iron uptake pathway, and reduced activities of ISC containing enzymes aconitase and succinate dehydrogenase, were observed in sdo1∆ yeast. In cells lacking Sdo1p, elevated levels of reactive oxygen species (ROS) and protein oxidation were reduced with iron chelation, using a cell impermeable iron chelator. In addition, the low activity of manganese superoxide dismutase (Sod2p) seen in sdo1∆ cells was improved with iron chelation, consistent with the presence of reactive iron from the ISC assembly pathway. In yeast lacking Sdo1p, the mitochondrial voltage-dependent anion channel (VDAC) Por1p is over-expressed and its deletion limits iron accumulation and increases activity of aconitase and succinate dehydrogenase.

CONCLUSIONS

We propose that oxidative stress from POR1 over-expression, resulting in impaired activity of ISC containing proteins and disruptions in iron homeostasis, may play a role in disease pathogenesis in SDS patients.

Overexpression of the peroxin Pex34p suppresses impaired acetate utilization in yeast lacking the mitochondrial aspartate/glutamate carrier Agc1p

PEX34, encoding a peroxisomal protein implicated in regulating peroxisome numbers, was identified as a high copy suppressor, capable of bypassing impaired acetate utilization of agc1∆ yeast. However, improved growth of agc1∆ yeast on acetate is not mediated through peroxisome proliferation. Instead, stress to the endoplasmic reticulum and mitochondria from PEX34 overexpression appears to contribute to enhanced acetate utilization of agc1∆ yeast. The citrate/2-oxoglutarate carrier Yhm2p is required for PEX34 stimulated growth of agc1∆ yeast on acetate medium, suggesting that the suppressor effect is mediated through increased activity of a redox shuttle involving mitochondrial citrate export. Metabolomic analysis also revealed redirection of acetyl-coenzyme A (CoA) from synthetic reactions for amino acids in PEX34 overexpressing yeast. We propose a model in which increased formation of products from the glyoxylate shunt, together with enhanced utilization of acetyl-CoA, promotes the activity of an alternative mitochondrial redox shuttle, partially substituting for loss of yeast AGC1.

Overexpression of Transcription Factor ZNF1 of Glycolysis Improves Bioethanol Productivity under High Glucose Concentration and Enhances Acetic Acid Tolerance of Saccharomyces cerevisiae

Saccharomyces cerevisiae offers an attractive platform for synthesis of biofuels and biochemical; however, robust strains that can withstand high substrate concentration and fermentation conditions are required. To improve the yield and productivity of bioethanol, modification of glucose metabolism and cellular stress adaptation is investigated. Specifically, the role of Znf1 transcription factor in metabolic regulation of glucose is characterized. Here, Znf1 is first shown to activate key genes in glycolysis, pyruvate metabolism, and alcoholic fermentation when glucose is provided as the sole carbon source. Under conditions of high glucose (20 g L^-1 ), overexpression of ZNF1 accelerated glucose consumption with only 0.67-0.80% of glucose remaining after 24 or 36 h of fermentation. Importantly, ZNF1 overexpression increases ethanol concentrations by 14-24% and achieves a maximum ethanol concentration of 76.12-88.60 g L^-1 . Ethanol productivity is increased 3.17-3.69 in strains overexpressing ZNF1 compared to 2.42-3.35 and 2.94-3.50 for the znf1Δ and wild-type strains, respectively. Moreover, strains overexpressing ZNF1 also display enhanced tolerance to osmotic and weak-acid stresses, important trait in alcoholic fermentation. Overexpresssion of key transcriptional activators of genes in glycolysis and stress responses appears to be an effective strategy to improve bioethanol productivity and enhance strain robustness.

Decreased accumulation of superoxide dismutase 2 within mitochondria in the yeast model of Shwachman-Diamond syndrome

Mutations in the human SBDS gene is the most common cause of Shwachman-Diamond syndrome (SDS). The SBDS protein participates in ribosome biogenesis; however, effects beyond reduced translation efficiency are thought to be involved in SDS progression. Impaired mitochondrial function has been reported for cells lacking either SBDS or Sdo1p, the Saccharomyces cerevisiae SBDS ortholog. To better understand how the loss of SBDS/Sdo1p leads to mitochondria damage, we utilized the S. cerevisiae model of SDS. Yeast deleted for SDO1 show increased oxidative damage to mitochondrial proteins and a marked decrease in protein levels and activity of mitochondrial superoxide dismutase 2 (Sod2p), a key enzyme involved in defense against oxidants. Immature forms of Sod2p are observed in sdo1∆ cells suggesting a defect in proteolysis of the presequence. Yeast deleted for CYM1, encoding a presequence protease, display a similar reduction in Sod2p activity as sdo1∆ cells, as well as elevated oxidative damage, to mitochondrial proteins. Sod2p protein levels and activity are largely restored in a por1∆ sdo1∆ strain, lacking the major mitochondrial voltage-dependent anion channel. Together these results indicate that mitochondrial insufficiency in sdo1∆ cells may be linked to the accumulation of immature presequence containing proteins and this effect is a consequence, at least in part, from loss of counter-regulation of Por1p by Sdo1p.

Interrogation of ethnomedicinal plants for synthetic lethality effects in combination with deficiency in the DNA repair endonuclease RAD1 using a yeast cell-based assay

ETHNOPHARMACOLOGICAL RELEVANCE

Plant materials used in this study were selected based on the ethnobotanical literature. Plants have either been utilized by Thai practitioners as alternative treatments for cancer or identified to exhibit anti-cancer properties.

AIM OF THE STUDY

To screen ethnomedicinal plants using a yeast cell-based assay for synthetic lethal interactions with cells deleted for RAD1, the yeast homologue of human ERCC4 (XPF) MATERIALS AND METHODS: Ethanolic extracts from thirty-two species of medicinal plants utilized in Thai traditional medicine were screened for synthetic lethal/sick interactions using a yeast cell-based assay. Cell growth was compared between the parental strain and rad1∆ yeast following exposure to select for specific toxicity of plant extracts. Candidate extracts were further examined for the mode of action using genetic and biochemical approaches.

RESULTS

Screening a library of ethanolic extracts from medicinal plants identified Bacopa monnieri and Colubrina asiatica as having synthetic lethal effects in the rad1∆ cells but not the parental strain. Synthetic lethal effects for B. monneiri extracts were more apparent and this plant was examined further. Genetic analysis indicates that pro-oxidant activities and defective excision repair pathways do not significantly contribute to enhanced sensitivity to B. monneiri extracts. Exposure to B. monneiri extracts resulted in nuclear fragmentation and elevated levels of ethidium bromide staining in rad1∆ yeast suggesting promotion of an apoptosis-like event. Growth inhibition also observed in the human Caco-2 cell line suggesting the effects of B. monnieri extracts on both yeast and human cells may be similar.

CONCLUSIONS

B. monneiri extracts may have utility in treatment of colorectal cancers that exhibit deficiency in ERCC4 (XPF).

Fungicide Xylaria sp. BCC 1067 extract induces reactive oxygen species and activates multidrug resistance system in Saccharomyces cerevisiae

AIM

To investigate antifungal potential of Xylaria sp. BIOTEC culture collection (BCC) 1067 extract against the model yeast Saccharomyces cerevisiae.

MATERIALS & METHODS

Antifungal property of extract, reactive oxygen species levels and cell survival were determined, using selected deletion strains.

RESULTS

Extract showed promising antifungal effect with minimal inhibitory concentration₁₀₀ and minimal fungicidal concentration of 500 and 1000 mg/l, respectively. Strong synergy was observed with fractional inhibitory concentration index value of 0.185 for the combination of 60.0 and 0.5 mg/l of extract and ketoconazole, respectively. Extract-induced intracellular reactive oxygen species levels in some oxidant-prone strains and mediated plasma membrane rupture. Antioxidant regulator Yap1, efflux transporter Pdr5 and ascorbate were pivotal to protect S. cerevisiae from extract cytotoxicity.

CONCLUSION

Xylaria sp. BCC 1067 extract is a potentially valuable source of novel antifungals.

Zinc cluster protein Znf1, a novel transcription factor of non-fermentative metabolism in Saccharomyces cerevisiae

The ability to rapidly respond to nutrient changes is a fundamental requirement for cell survival. Here, we show that the zinc cluster regulator Znf1 responds to altered nutrient signals following glucose starvation through the direct control of genes involved in non-fermentative metabolism, including those belonged to the central pathways of gluconeogenesis (PCK1, FBP1 and MDH2), glyoxylate shunt (MLS1 and ICL1) and the tricarboxylic acid cycle (ACO1), which is demonstrated by Znf1-binding enrichment at these promoters during the glucose-ethanol shift. Additionally, reduced Pck1 and Fbp1 enzymatic activities correlate well with the data obtained from gene transcription analysis. Cells deleted for ZNF1 also display defective mitochondrial morphology with unclear structures of the inner membrane cristae when grown in ethanol, in agreement with the substantial reduction in the ATP content, suggesting for roles of Znf1 in maintaining mitochondrial morphology and function. Furthermore, Znf1 also plays a role in tolerance to pH and osmotic stress, especially during the oxidative metabolism. Taken together, our results clearly suggest that Znf1 is a critical transcriptional regulator for stress adaptation during non-fermentative growth with some partial overlapping targets with previously reported regulators in Saccharomyces cerevisiae.

Heat-washout measurements compared to distal blood pressure and perfusion in orthopaedic patients with foot ulcers

Distal blood pressure and local skin perfusion pressure were compared to measurement of blood flow rate (BFR) measured by the heat-washout method in orthopaedic patients with and without diabetes, all with a foot ulcer in one foot, compared to healthy controls. The correlation was good between heat-washout and distal blood pressure in patients with diabetes with and without an ulcer (P = 0·024 and 0·059, respectively). The correlation was weak in patients without diabetes with and without an ulcer, most probably due to power problems (P = 0·118 and 0·116, respectively). The correlation in the healthy controls was poor (P = 0·333 and 0·685 for right and left 1. Toe, respectively) probably because not all measurements were performed under optimal conditions with maximally dilated arterioles and warm hands and feet. The patients already have maximally dilated arterioles to extract the maximal amount of oxygen from the surrounding tissue, and therefore, measurements are easier made in these subjects. BFR in the first toe increased significantly in all patients when the foot was moved from heart level to 50 cm below heart level (P = between 0·03 and 0·05) as previously seen in patients with claudication. There was no statistical difference in the healthy controls, consistent with previous findings. These results may indicate that the heat-washout method can be used as an alternative to strain gauge blood pressure in the evaluation of peripheral artery disease and wound healing potentials. Furthermore, the heat-washout measurements can be used bedside.

Improper protein trafficking contributes to artemisinin sensitivity in cells lacking the KDAC Rpd3p

Lysine deacetylases (KDACs) inhibitors may have therapeutic value in anti-malarial combination therapies with artemisinin. To evaluate connections between KDACs and artemisinin, Saccharomyces cerevisiae deletion mutants in KDAC genes were assayed. Deletion of RPD3, but not other KDAC genes, resulted in strong sensitivity to artemisinin, which was also observed in sit4Δ mutants with impaired endoplasmic reticulum (ER) to Golgi protein trafficking. Decreased accumulation of the transporters Pdr5p, Fur4p, and Tat2p was observed in rpd3Δ and sit4Δ cells. The unfolded protein response is induced in rpd3Δ cells consistent with retention of proteins in the ER. Disruption of protein trafficking appears to sensitize cells to artemisinin and targeting these pathways may be useful as part of artemisinin based anti-malarial therapy.

Screening of SLC25A13 mutation in the Thai population

AIM: To determine the prevalence of SLC25A13 mutations in the Thai population.

METHODS: A total of 1537 subjects representing the Thai population were screened for a novel pathologic allele p.Met1? (c.2T > C) and six previously known common SLC25A13 mutations: [I] (c.851_854delGTAT), [II] (g.IVS11 + 1G > A), [III] (c.1638_1660dup), [IV] (p.S225X), [V] (IVS13 + 1G > A), and [XIX] (g.IVS16ins3kb) using a newly developed TaqMan and established HybProbe assay, respectively. Sanger sequencing was employed for specimens showing an aberrant peak to confirm the targeted mutation as well as the unknown aberrant peaks detected. Frequencies of the mutations identified were compared in each region. Carrier frequency and disease prevalence of citrin deficiency caused by SCL25A13 mutations were estimated.

RESULTS: p.Met1? was identified in the heterozygous state in 85 individuals, giving a carrier frequency of 1/18, which suggests possible selective advantage of this variant. The question of p.Met1? homozygote lethality remains unanswered which may serve as an explanation as to why this homozygote has yet to be identified in patients/controls even with high allele frequency. The p.Met1? mutation has rarely been studied in populations other than Thai and Chinese; therefore, may have been overlooked. Development of the TaqMan assay in the present study would allow a simple, rapid, and cost-effective method for mass screening. Heterozygous mutations: [XIX] and [I] were identified in 17 individuals, giving a carrier rate of 1/90 and a calculated homozygote rate of 1/33000. Two novel variants, g.IVS11 + 17C > G and c.1311C > T, of unknown clinical significance were identified at low frequency.

CONCLUSION: This study highlighted the current underestimation of citrin deficiency and suggests the possible selective advantage of the p.Met1? allele.

Prediction of the functional effect of novel SLC25A13 variants using a S. cerevisiae model of AGC2 deficiency

AGC2, a member of the mitochondrial carrier protein family, is as an aspartate-glutamate carrier and is important for urea synthesis and the maintenance of the malate-aspartate shuttle. Mutations in SLC25A13, the gene encoding AGC2, result in two age dependent disorders: neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) and type II citrullinemia (CTLN2). The clinical features of CTLN2 are very similar to those of other urea cycle disorders making a clear diagnosis difficult. Analysis of the SLC25A13 gene sequence can provide a definitive diagnosis, however the predictive value of DNA sequencing requires that the disease association of variants be characterized. We utilized the yeast Saccharomyces cerevisiae lacking AGC1 as a model system to study the effect on the function of AGC2 variants and confirmed that this system is capable of distinguishing between AGC2 variants with normal (p.Pro632Leu) or impaired function (p.Gly437Glu, p.Gly531Asp, p.Thr546Met, p.Leu598Arg and p.Glu601Lys). Three novel AGC2 genetic variants, p.Met1? (c.2T>C), p.Pro502Leu (c.1505C>T), and p.Arg605Gln (c.1814G>A) were investigated and our analysis revealed that p.Pro502Leu and p.Arg605Gln substitutions in the AGC2 protein were without effect and these variants were fully functional. The p.Met1? mutant is capable of expressing a truncated p.Met1_Phe34del AGC2 variant, however this protein is not functional due to disruptions in a calcium binding EF hand as well as incorrect intracellular localization. Our study demonstrates that the characterization of AGC2 expressed in yeast cells is a powerful technique to investigate AGC2 variants, and this analysis should aid in establishing the disease association of novel variants.

Changes in calcitropic hormones, bone markers and insulin-like growth factor I (IGF-I) during pregnancy and postpartum: a controlled cohort study

Pregnancy and lactation cause major changes in calcium homeostasis and bone metabolism. This population-based cohort study presents the physiological changes in biochemical indices of calcium homeostasis and bone metabolism during pregnancy and lactation

INTRODUCTION

We describe physiological changes in calcium homeostasis, calcitropic hormones and bone metabolism during pregnancy and lactation.

METHODS

We studied 153 women planning pregnancy (n=92 conceived) and 52 non-pregnant, age-matched female controls. Samples were collected prior to pregnancy, once each trimester and 2, 16 and 36 weeks postpartum. The controls were followed in parallel.

RESULTS

P-estradiol (E2), prolactin and 1,25-dihydroxyvitamin D (1,25(OH)2D) increased (p<0.001) during pregnancy, whereas plasma levels of parathyroid hormone (P-PTH) and calcitonin decreased (p<0.01). Insulin-like growth factor I (IGF-I) was suppressed (p<0.05) in early pregnancy but peaked in the third trimester. Postpartum, E2 was low (p<0.05); prolactin decreased according to lactation status (p<0.05). 1,25(OH)2D was normal and IGF-I was again reduced (p<0.05). P-PTH and calcitonin increased postpartum. From early pregnancy, markers of bone resorption and formation rose and fall, respectively (p<0.001). From the third trimester, bone formation markers increased in association with IGF-I changes (p<0.01). Postpartum increases in bone turnover markers were associated with lactation status (p<0.001). During lactation, plasma phosphate was increased, whereas calcium levels tended to be decreased which may stimulate PTH levels during and after prolonged lactation.

CONCLUSION

The increased calcium requirements in early pregnancy are not completely offset by increased intestinal calcium absorption caused by high 1,25(OH)2D since changes in bone markers indicated a negative bone balance. The rise in bone formation in late pregnancy may be initiated by a spike in IGF-I levels. The high bone turnover in lactating women may be related to high prolactin and PTH levels, low E2 levels and perhaps increased parathyroid hormone-related protein levels.

The effect of phosphate accumulation on metal ion homeostasis in Saccharomyces cerevisiae

Much of what is currently understood about the cell biology of metals involves their interactions with proteins. By comparison, little is known about interactions of metals with intracellular inorganic compounds such as phosphate. Here we examined the role of phosphate in metal metabolism in vivo by genetically perturbing the phosphate content of Saccharomyces cerevisiae cells. Yeast pho80 mutants cannot sense phosphate and have lost control of phosphate uptake, storage, and metabolism. We report here that pho80 mutants specifically elevate cytosolic and nonvacuolar levels of phosphate and this in turn causes a wide range of metal homeostasis defects. Intracellular levels of the hard-metal cations sodium and calcium increase dramatically, and cells become susceptible to toxicity from the transition metals manganese, cobalt, zinc, and copper. Disruptions in phosphate control also elicit an iron starvation response, as pho80 mutants were seen to upregulate iron transport genes. The iron-responsive transcription factor Aft1p appears activated in cells with high phosphate content in spite of normal intracellular iron levels. The high phosphate content of pho80 mutants can be lowered by mutating Pho4p, the transcription factor for phosphate uptake and storage genes. Such lowering of phosphate content by pho4 mutations reversed the high calcium and sodium content of pho80 mutants and prevented the iron starvation response. However, pho4 mutations only partially reversed toxicity from heavy metals, representing a novel outcome of phosphate dysregulation. Overall, these studies underscore the importance of maintaining a charge balance in the cell; a disruption in phosphate metabolism can dramatically impact on metal homeostasis.

CGRP receptor antagonist olcegepant (BIBN4096BS) does not prevent glyceryl trinitrate-induced migraine

There is a striking similarity between the migraine-provoking effect of the nitric oxide (NO) donor glyceryl trinitrate (GTN) and that of calcitonin gene-related peptide (CGRP). We tested the hypothesis that NO releases CGRP to cause the delayed migraine attack after GTN.

Methods: In a double-blind-cross-over study, 13 migraine without aura (MO) patients were administered GTN 0.5 µg/kg/minute for 20 minutes and subsequently BIBN4096BS (olcegepant) 10 mg or placebo. Headache scores and development of MO were followed for 24 hours.

Results: MO developed in seven of 13 with olcegepant and in nine of 13 with placebo ( p = 0.68). The headache scores were similar after the two treatments ( p = 0.58). Thus CGRP receptor blockade did not prevent GTN-induced migraine.

Conclusions: The present study indicates that NO does not induce migraine by liberating CGRP. The most likely explanation for our findings is that CGRP has its effect higher than NO in the cascade of events leading to MO attacks.

A novel giant peroxisomal superoxide dismutase motif-containing protein

Oxidative glutamate toxicity in the neuronal cell line HT22 is a model for neuronal cell death by oxidative stress. In this model, extracellular glutamate blocks cystine uptake via the glutamate/cystine antiporter system x(c)(), eventually leading to depletion of the antioxidant glutathione and cell death. We used subtractive suppression hybridization and a screening procedure using various HT22 sublines to identify transcripts relevantly upregulated in resistance to oxidative glutamate toxicity. One of these coded for a novel protein of 3440 amino acids comprising a superoxide dismutase (SOD) motif, which we named TIGR for "transcript increased in glutamate resistance." TIGR is mainly expressed in the nervous system in cortical pyramidal and hippocampal neurons. Intracellularly, TIGR colocalizes with catalase, strongly suggesting a peroxisomal localization. Overexpression of TIGR but not of a mutant lacking two conserved histidine residues in the SOD motif increased SOD activity and protected against oxidative stress in mammalian cells, but had no direct SOD activity in yeast. We conclude that this novel giant peroxisomal protein is implicated in resistance to oxidative stress. Despite the presence of a SOD motif, which is necessary for protection in mammalian cells, the protein is not a functional SOD, but might be involved in SOD activity.

A clinally varying promoter polymorphism associated with adaptive variation in wing size in Drosophila

Body size often shows adaptive clines in many ectotherms across altitude and latitude, but little is known about the genetic basis of these adaptive clines. Here we identify a polymorphism in the Dca (Drosophila cold acclimation) gene in Drosophila melanogaster that influences wing size, affects wing:thorax allometry and also controls a substantial proportion of the clinal wing-size variation. A polymorphism in the promoter region of Dca had two common alleles showing strong reciprocal clinal variation in frequency with latitude along the east coast of Australia. The Dca-237 allele increased towards the tropics where wing size is smaller. A within-population association study highlighted that an increase in the frequency of this allele decreased wing size but did not influence thorax size. A manipulated increase in the level of expression of Dca achieved through UAS-GAL4 was associated with a decrease in wing size but had no effect on thorax size. This was consistent with higher Dca expression levels in family lines with higher frequency of the Dca-237 allele. Genetic variation in the promoter region of the Dca gene appears to influence adaptive size variation in the eastern Australian cline of Drosophila melanogaster and accounts for more than 10% of the genetic variation in size within and between populations.

The interaction of mitochondrial iron with manganese superoxide dismutase

Superoxide dismutase 2 (SOD2) is one of the rare mitochondrial enzymes evolved to use manganese as a cofactor over the more abundant element iron. Although mitochondrial iron does not normally bind SOD2, iron will misincorporate into Saccharomyces cerevisiae Sod2p when cells are starved for manganese or when mitochondrial iron homeostasis is disrupted by mutations in yeast grx5, ssq1, and mtm1. We report here that such changes in mitochondrial manganese and iron similarly affect cofactor selection in a heterologously expressed Escherichia coli Mn-SOD, but not a highly homologous Fe-SOD. By x-ray absorption near edge structure and extended x-ray absorption fine structure analyses of isolated mitochondria, we find that misincorporation of iron into yeast Sod2p does not correlate with significant changes in the average oxidation state or coordination chemistry of bulk mitochondrial iron. Instead, small changes in mitochondrial iron are likely to promote iron-SOD2 interactions. Iron binds Sod2p in yeast mutants blocking late stages of iron-sulfur cluster biogenesis (grx5, ssq1, and atm1), but not in mutants defective in the upstream Isu proteins that serve as scaffolds for iron-sulfur biosynthesis. In fact, we observed a requirement for the Isu proteins in iron inactivation of yeast Sod2p. Sod2p activity was restored in mtm1 and grx5 mutants by depleting cells of Isu proteins or using a dominant negative Isu1p predicted to stabilize iron binding to Isu1p. In all cases where disruptions in iron homeostasis inactivated Sod2p, we observed an increase in mitochondrial Isu proteins. These studies indicate that the Isu proteins and the iron-sulfur pathway can donate iron to Sod2p.

Changes in cerebral blood flow after acetazolamide: an experimental study comparing near-infrared spectroscopy and SPECT

BACKGROUND AND PURPOSE

It is important to find a reliable and bedside method, which can estimate the cerebral blood flow (CBF) of patients in clinical settings. Estimation of CBF by calculating a blood flow index (BFI) using continuous wave near-infrared spectroscopy (CW-NIRS) and indocyanine green (ICG) as an i.v. tracer has been proposed to be a feasible and promising method. To validate if the BFI method can detect relative changes in CBF we compared data with the established method (133)Xenon single photon emission computer tomography ((133)Xe-SPECT).

METHODS

Ten healthy subjects were investigated before and after a bolus of acetazolamide. NIRS data were obtained using a multi source detector separation configuration in order to assess a corrected BFI (BFI(corr)) value, which attempts to eliminate contamination of skin blood flow.

RESULTS

Data obtained showed no significant correlation between CBF changes measured by (133)Xe-SPECT and BFI(corr) (0.133, P = 0.732). After acetazolamide, a 49% increase in CBF was detected using the (133)Xe-SPECT method, whereas no changes in any ICG variables were observed after acetazolamide.

CONCLUSION

The study shows that it is not possible to obtain reliable BFI data, which reflect changes in CBF after acetazolamide infusion, using the CW-NIRS and ICG method.

Activation of Cu,Zn-superoxide dismutase in the absence of oxygen and the copper chaperone CCS

Eukaryotic Cu,Zn-superoxide dismutases (SOD1s) are generally thought to acquire the essential copper cofactor and intramolecular disulfide bond through the action of the CCS copper chaperone. However, several metazoan SOD1s have been shown to acquire activity in vivo in the absence of CCS, and the Cu,Zn-SOD from Caenorhabditis elegans has evolved complete independence from CCS. To investigate SOD1 activation in the absence of CCS, we compared and contrasted the CCS-independent activation of C. elegans and human SOD1 to the strict CCS-dependent activation of Saccharomyces cerevisiae SOD1. Using a yeast expression system, both pathways were seen to acquire copper derived from cell surface transporters and compete for the same intracellular pool of copper. Like CCS, CCS-independent activation occurs rapidly with a preexisting pool of apo-SOD1 without the need for new protein synthesis. The two pathways, however, strongly diverge when assayed for the SOD1 disulfide. SOD1 molecules that are activated without CCS exhibit disulfide oxidation in vivo without oxygen and under copper-depleted conditions. The strict requirement for copper, oxygen, and CCS in disulfide bond oxidation appears exclusive to yeast SOD1, and we find that a unique proline at position 144 in yeast SOD1 is responsible for this disulfide effect. CCS-dependent and -independent pathways also exhibit differential requirements for molecular oxygen. CCS activation of SOD1 requires oxygen, whereas the CCS-independent pathway is able to activate SOD1s even under anaerobic conditions. In this manner, Cu,Zn-SOD from metazoans may retain activity over a wide range of physiological oxygen tensions.

Down-regulation of a manganese transporter in the face of metal toxicity

The yeast Smf1p Nramp manganese transporter is posttranslationally regulated by environmental manganese. Smf1p is stabilized at the cell surface with manganese starvation, but is largely degraded in the vacuole with physiological manganese through a mechanism involving the Rsp5p adaptor complex Bsd2p/Tre1p/Tre2p. We now describe an additional level of Smf1p regulation that occurs with toxicity from manganese, but not other essential metals. This regulation is largely Smf1p-specific. As with physiological manganese, toxic manganese triggers vacuolar degradation of Smf1p by trafficking through the multivesicular body. However, regulation by toxic manganese does not involve Bsd2p/Tre1p/Tre2p. Toxic manganese triggers both endocytosis of cell surface Smf1p and vacuolar targeting of intracellular Smf1p through the exocytic pathway. Notably, the kinetics of vacuolar targeting for Smf1p are relatively slow with toxic manganese and require prolonged exposures to the metal. Down-regulation of Smf1p by toxic manganese does not require transport activity of Smf1p, whereas such transport activity is needed for Smf1p regulation by manganese starvation. Furthermore, the responses to manganese starvation and manganese toxicity involve separate cellular compartments. We provide evidence that manganese starvation is sensed within the lumen of the secretory pathway, whereas manganese toxicity is sensed within an extra-Golgi/cytosolic compartment of the cell.

The overlapping roles of manganese and Cu/Zn SOD in oxidative stress protection

In various organisms, high intracellular manganese provides protection against oxidative damage through unknown pathways. Herein we use a genetic approach in Saccharomyces cerevisiae to analyze factors that promote manganese as an antioxidant in cells lacking Cu/Zn superoxide dismutase (sod1 Delta). Unlike certain bacterial systems, oxygen resistance in yeast correlates with high intracellular manganese without a lowering of iron. This manganese for antioxidant protection is provided by the Nramp transporters Smf1p and Smf2p, with Smf1p playing a major role. In fact, loss of manganese transport by Smf1p together with loss of the Pmr1p manganese pump is lethal to sod1 Delta cells despite normal manganese SOD2 activity. Manganese-phosphate complexes are excellent superoxide dismutase mimics in vitro, yet through genetic disruption of phosphate transport and storage, we observed no requirement for phosphate in manganese suppression of oxidative damage. If anything, elevated phosphate correlated with profound oxidative stress in sod1 Delta mutants. The efficacy of manganese as an antioxidant was drastically reduced in cells that hyperaccumulate phosphate without effects on Mn SOD activity. Non-SOD manganese can provide a critical backup for Cu/Zn SOD1, but only under appropriate physiologic conditions.

Nucleotide diversity in the Hsp90 gene in natural populations of Drosophila melanogaster from Australia

Hsp90 is regarded as one of the best candidates for an evolved mechanism that regulates the expression of genetic and phenotypic variability. We examined nucleotide diversity in both the promoter and coding regions of Hsp90, the gene which encodes Hsp90 in Drosophila, in natural populations of Drosophila melanogaster from eastern Australia. We found that Hsp90 is polymorphic for only two nonsynonymous changes in the coding region, both of which are deletions of a lysine residue. One of these lysine deletions was in complete linkage disequilibrium with the inversion In(3L)P, and showed a significant association with latitude. The other lysine deletion reported here for the first time varied from 0 to 15% in natural populations, but did not show a clinal pattern. The regulatory and coding regions of Hsp90 showed very low nucleotide diversity compared to other nuclear genes, and chromosomes containing In(3L)P had lower levels of nucleotide diversity than the standard arrangements. Non-neutral evolution of Hsp90 was not supported by analyses of either the regulatory or coding regions of the gene. These results are discussed within the context of Hsp90 variation being involved in thermotolerance as well as the expression of genetic and phenotypic variability.

Instability of superoxide dismutase 1 of Drosophila in mutants deficient for its cognate copper chaperone

Copper,zinc superoxide dismutase (SOD1) in mammals is activated principally via a copper chaperone (CCS) and to a lesser degree by a CCS-independent pathway of unknown nature. In this study, we have characterized the requirement for CCS in activating SOD1 from Drosophila. A CCS-null mutant (Ccs(n)(29)(E)) of Drosophila was created and found to phenotypically resemble Drosophila SOD1-null mutants in terms of reduced adult life span, hypersensitivity to oxidative stress, and loss of cytosolic aconitase activity. However, the phenotypes of CCS-null flies were less severe, consistent with some CCS-independent activation of Drosophila SOD1 (dSOD1). Yet SOD1 activity was not detectable in Ccs(n)(29)(E) flies, due largely to a striking loss of SOD1 protein. In contrast, human SOD1 expressed in CCS-null flies is robustly active and rescues the deficits in adult life span and sensitivity to oxidative stress. The dependence of dSOD1 on CCS was also observed in a yeast expression system where the dSOD1 polypeptide exhibited unusual instability in CCS-null (ccs1Delta) yeast. The residual dSOD1 polypeptide in ccs1Delta yeast was nevertheless active, consistent with CCS-independent activation. Stability of dSOD1 in ccs1Delta cells was readily restored by expression of either yeast or Drosophila CCS, and this required copper insertion into the enzyme. The yeast expression system also revealed some species specificity for CCS. Yeast SOD1 exhibits preference for yeast CCS over Drosophila CCS, whereas dSOD1 is fully activated with either CCS molecule. Such variation in mechanisms of copper activation of SOD1 could reflect evolutionary responses to unique oxygen and/or copper environments faced by divergent species.

The effects of glutaredoxin and copper activation pathways on the disulfide and stability of Cu,Zn superoxide dismutase

Mutations in Cu,Zn superoxide dismutase (SOD1) can cause amyotrophic lateral sclerosis (ALS) through mechanisms proposed to involve SOD1 misfolding, but the intracellular factors that modulate folding and stability of SOD1 are largely unknown. By using yeast and mammalian expression systems, we demonstrate here that SOD1 stability is governed by post-translational modification factors that target the SOD1 disulfide. Oxidation of the human SOD1 disulfide in vivo was found to involve both the copper chaperone for SOD1 (CCS) and the CCS-independent pathway for copper activation. When both copper pathways were blocked, wild type SOD1 stably accumulated in yeast cells with a reduced disulfide, whereas ALS SOD1 mutants A4V, G93A, and G37R were degraded. We describe here an unprecedented role for the thiol oxidoreductase glutaredoxin in reducing the SOD1 disulfide and destabilizing ALS mutants. Specifically, the major cytosolic glutaredoxin of yeast was seen to reduce the intramolecular disulfide of ALS SOD1 mutant A4V SOD1 in vivo and in vitro. By comparison, glutaredoxin was less reactive toward the disulfide of wild type SOD1. The apo-form of A4V SOD1 was highly reactive with glutaredoxin but not SOD1 containing both copper and zinc. Glutaredoxin therefore preferentially targets the immature form of ALS mutant SOD1 lacking metal co-factors. Overall, these studies implicate a critical balance between cellular reductants such as glutaredoxin and copper activation pathways in controlling the disulfide and stability of SOD1 in vivo.

Activation of CuZn Superoxide Dismutases from Caenorhabditis elegans Does Not Require the Copper Chaperone CCS

Reactive oxygen species are produced as the direct result of aerobic metabolism and can cause damage to DNA, proteins, and lipids. A principal defense against reactive oxygen species involves the superoxide dismutases (SOD) that act to detoxify superoxide anions. Activation of CuZn-SODs in eukaryotic cells occurs post-translationally and is generally dependent on the copper chaperone for SOD1 (CCS), which inserts the catalytic copper cofactor and catalyzes the oxidation of a conserved disulfide bond that is essential for activity. In contrast to other eukaryotes, the nematode Caenorhabditis elegans does not contain an obvious CCS homologue, and we have found that the C. elegans intracellular CuZn-SODs (wSOD-1 and wSOD-5) are not dependent on CCS for activation when expressed in Saccharomyces cerevisiae. CCS-independent activation of CuZn-SODs is not unique to C. elegans; however, this is the first organism identified that appears to exclusively use this alternative pathway. As was found for mammalian SOD1, wSOD-1 exhibits a requirement for reduced glutathione in CCS-independent activation. Unexpectedly, wSOD-1 was inactive even in the presence of CCS when glutathione was depleted. Our investigation of the cysteine residues that form the disulfide bond in wSOD-1 suggests that the ability of wSODs to readily form this disulfide bond may be the key to obtaining high levels of activation through the CCS-independent pathway. Overall, these studies demonstrate that the CuZn-SODs of C. elegans have uniquely evolved to acquire copper without the copper chaperone and this may reflect the lifestyle of this organism.

Manganese activation of superoxide dismutase 2 in the mitochondria of Saccharomyces cerevisiae

Manganese-dependent superoxide dismutase 2 (SOD2) in the mitochondria plays a key role in protection against oxidative stress. Here we probed the pathway by which SOD2 acquires its manganese catalytic cofactor. We found that a mitochondrial localization is essential. A cytosolic version of Saccharomyces cerevisiae Sod2p is largely apo for manganese and is only efficiently activated when cells accumulate toxic levels of manganese. Furthermore, Candida albicans naturally produces a cytosolic manganese SOD (Ca SOD3), yet when expressed in the cytosol of S. cerevisiae, a large fraction of Ca SOD3 also remained manganese-deficient. The cytosol of S. cerevisae cannot readily support activation of Mn-SOD molecules. By monitoring the kinetics for metalation of S. cerevisiae Sod2p in vivo, we found that prefolded Sod2p in the mitochondria cannot be activated by manganese. Manganese insertion is only possible with a newly synthesized polypeptide. Furthermore, Sod2p synthesis appears closely coupled to Sod2p import. By reversibly blocking mitochondrial import in vivo, we noted that newly synthesized Sod2p can enter mitochondria but not a Sod2p polypeptide that was allowed to accumulate in the cytosol. We propose a model in which the insertion of manganese into eukaryotic SOD2 molecules is driven by the protein unfolding process associated with mitochondrial import.

Mutations in Saccharomyces cerevisiae Iron-Sulfur Cluster Assembly Genes and Oxidative Stress Relevant to Cu,Zn Superoxide Dismutase

Saccharomyces cerevisiae lacking Cu,Zn superoxide dismutase (SOD1) show several metabolic defects including aerobic blockages in methionine and lysine biosynthesis. We have previously shown that mutations in genes implicated in the formation of iron-sulfur clusters, designated seo (suppressors of endogenous oxidation), reverse the oxygen-dependent methionine and lysine auxotrophies of a sod1Delta strain. We now report the surprising finding that seo mutants do not reduce oxidative damage as shown by the lack of reduction of EPR-detectable "free" iron, which is characteristic of sod1Delta mutants. In fact, they exhibit increased oxidative damage as evidenced by increased accumulation of protein carbonyls. The seo class of mutants overaccumulates mitochondrial iron, and this iron accumulation is critical for suppression of the sod1Delta biosynthetic defects. Blocking overaccumulation of mitochondrial iron abolished the ability of the seo mutants to suppress the sod1Delta auxotrophies. By contrast, increasing the mitochondrial iron content of sod1Delta yeast using high copy MMT1, which encodes a mitochondrial iron transporter, was sufficient to mimic the seo mutants. Our studies indicated that suppression of the sod1Delta methionine auxotrophy was dependent on the pentose phosphate pathway, which is a major source of NADPH production. By comparison, the sod1Delta lysine auxotrophy appears to be reversed in the seo mutants by increased expression of genes in the lysine biosynthetic pathway, perhaps through sensing of mitochondrial damage by the retrograde response.

The Saccharomyces cerevisiae high affinity phosphate transporter encoded by PHO84 also functions in manganese homeostasis

In the bakers' yeast Saccharomyces cerevisiae, high affinity manganese uptake and intracellular distribution involve two members of the Nramp family of genes, SMF1 and SMF2. In a search for other genes involved in manganese homeostasis, PHO84 was identified. The PHO84 gene encodes a high affinity inorganic phosphate transporter, and we find that its disruption results in a manganese-resistant phenotype. Resistance to zinc, cobalt, and copper ions was also demonstrated for pho84Delta yeast. When challenged with high concentrations of metals, pho84Delta yeast have reduced metal ion accumulation, suggesting that resistance is due to reduced uptake of metal ions. Pho84p accounted for virtually all the manganese accumulated under metal surplus conditions, demonstrating that this transporter is the major source of excess manganese accumulation. The manganese taken in via Pho84p is indeed biologically active and can not only cause toxicity but can also be incorporated into manganese-requiring enzymes. Pho84p is essential for activating manganese enzymes in smf2Delta mutants that rely on low affinity manganese transport systems. A role for Pho84p in manganese accumulation was also identified in a standard laboratory growth medium when high affinity manganese uptake is active. Under these conditions, cells lacking both Pho84p and the high affinity Smf1p transporter accumulated low levels of manganese, although there was no major effect on activity of manganese-requiring enzymes. We conclude that Pho84p plays a role in manganese homeostasis predominantly under manganese surplus conditions and appears to be functioning as a low affinity metal transporter.

The many highways for intracellular trafficking of metals

Metal ions such as copper and manganese represent a unique problem to living cells in that these ions are not only essential co-factors for metalloproteins, but are also potentially toxic. To aid in the homeostatic balance of essential but toxic metals, cells have evolved with a complex network of metal trafficking pathways. The object of such pathways is two-fold: to prevent accumulation of the metal in the freely reactive form (metal detoxification pathways) and to ensure proper delivery of the ion to target metalloproteins (metal utilization pathways). Much of what we currently know regarding these complex pathways of metal trafficking has emerged from molecular genetic studies in baker's yeast, Saccharomyces cerevisiae. In this review, we shall briefly highlight the current understanding of factors that function in the trafficking and handling of copper, including copper detoxification factors, copper transporters and copper chaperones. In addition, very recent findings on the players involved in manganese trafficking will be presented. The goal is to provide a paradigm for the intracellular handling of metals that may be applied in a more general sense to metals that serve essential functions in biology.

Engineering of metallothionein-3 neuroinhibitory activity into the inactive isoform metallothionein-1

The third isoform of mammalian metallothioneins (MT-3), mainly expressed in brain and down-regulated in Alzheimer's disease, exhibits neuroinhibitory activity in vitro and a highly flexible structure that distinguishes it from the widely expressed MT-1/-2 isoforms. Previously, we showed that two conserved prolyl residues of MT-3 are crucial for both the bioactivity and cluster dynamics of this isoform. We have now used genetic engineering to introduce these residues into mouse MT-1. The S6P,S8P MT-1 mutant is inactive in neuronal survival assays. However, the additional introduction of the unique Thr5 insert of MT-3 resulted in a bioactive MT-1 form. Temperature-dependent and saturation transfer (113)Cd NMR experiments performed on the (113)Cd-reconstituted wild-type and mutant Cd(7)-MT-1 forms revealed that the gain of MT-3-like neuronal inhibitory activity is paralleled by an increase in conformational flexibility and intersite metal exchange in the N-terminal Cd(3)-thiolate cluster. The observed correlation suggests that structure/cluster dynamics are critical for the biological activity of MT-3. We propose that the interplay between the specific Pro-induced conformational requirements and those of the metal-thiolate bonds gives rise to an alternate and highly fluctuating cluster ensemble kinetically trapped by the presence of the (5)TCPCP(9) motif. The functional significance of such heterogeneous cluster ensemble is discussed.

Characterization of human soluble high and low activity catechol-O-methyltransferase catalyzed catechol estrogen methylation

The major detoxification pathway of the carcinogenic catechol estrogens is methylation by catechol- -methyltransferase (COMT). It has been hypothesized that the enzyme encoded by the low-activity allele (COMT(L) ) has a lower catalytic activity for catechol estrogen methylation than that encoded by the high activity allele (COMT(H) ). We expressed and purified human soluble (S)-COMT(H) and S-COMT(L) in and characterized the methylation of 2- and 4-hydroxyestradiol (2- and 4-OH-E2). There were no differences between the kinetic parameters for COMT(H) and COMT(L). The kinetic parameters for S-adenosylmethionine (SAM), the methyl donor in these reactions, also did not differ for COMT(H) and COMT(L). S-adenosylhomocysteine, the demethylated SAM metabolite, inhibited methylation of the catechol estrogens in a non-competitive manner similarly for COMT(H) and COMT(L). Each COMT substrate tested inhibited the methylation of other substrates in a mixed competitive and non-competitive fashion similarly for COMT(H) and COMT(L). Furthermore, in cytosolic fractions of COMT(HH)(MCF-10A and ZR-75-1) and COMT(LL)(MCF-7 and T47D) human breast epithelial cell lines, no differences were detected between the kinetic parameters of COMT with respect to 2- and 4-OH-E2 methylation; nor were COMT protein levels associated with the COMT genotype. These data suggest that the decreased COMT enzymatic activity that has been detected in human tissue in association with the COMT(L) allele is not reflected by differences in the affinity or capacity of COMT(H) and COMT(L) for catechol estrogen methylation. These results raise the question of what accounts for the difference in COMT activity associated with the COMT(HH) and COMT(LL) genotypes in human tissue.

Regulation of Saccharomyces cerevisiae FET4 by oxygen and iron

Saccharomyces cerevisiae expresses two distinct iron transport systems under aerobic and anaerobic conditions. The high affinity transporters, Ftr1p and Fet3p, are primarily expressed in oxygenated cultures, whereas anaerobic conditions induce the low affinity iron transporter, Fet4p. The oxygen regulation of FET4 was found to involve the Rox1p transcriptional repressor. The physiological significance of this control by Rox1p is twofold. First, FET4 repression by Rox1p under oxygenated conditions helps minimize metal toxicity. Sensitivity towards cadmium was high in either anaerobically grown wild-type yeast or in oxygenated rox1Delta strains, and in both cases cadmium toxicity was reversed by FET4 mutations. Secondly, the loss of Rox1p repression under anaerobic conditions serves to induce FET4 and facilitate continual accumulation of iron. We noted that fet4 mutants accumulate lower levels of iron under anaerobic conditions. Regulation of FET4 was examined using FET4-lacZ reporters. We found that FET4 contains a complex promoter regulated both by oxygen and iron status. The region surrounding approximately -960 to -490 contains two consensus Rox1p binding sites and mediates Rox1p, but not iron control of FET4. Sequences downstream of -490 harbor a consensus binding site for the iron regulatory factor Aft1p that is essential for iron regulation in wild-type strains. In addition, a secondary mode of iron regulation becomes evident in strains lacking AFT1. The induction by iron limitation in conjunction with low oxygen is more than additive, suggesting that these activities are synergistic. Fet4p is not the only metal transporter that is negatively regulated by oxygen; we find that Rox1p also represses S. cerevisiae SMF3, proposed to function in vacuolar iron transport. This oxygen control of iron transporter gene expression is part of an adaptation response to changes in the redox state of transition metals.

Hypertension and renovascular disease: follow-up on 100 renal vein renin samplings

The clinical value of renal vein renin sampling (RVRS) as a prognostic tool in the treatment of renovascular hypertension was evaluated. One hundred consecutive patients were included over a 4-year period of time. About half of the patients (49%) were treated interventionally by PTRA (21%), nephrectomy (20%), or vascular surgery (8%). Seven patients (15%) were cured and 15 (32%) had improved (reduction in antihypertensive medicine) after 6 months follow-up, whereas three patients (6%) were cured and 12 (26%) improved after 3-4 years follow-up. Thus, the number of patients cured or improved is comparable with the results from our department reported 20 years ago. However, in the present report, more than twice as many patients were enrolled, leading to double costs. Different indices of lateralisation of the renin generation were calculated for the use in cases of a shrunken kidney (functional share < or =15%). None of the indices clearly discriminated between the patients who did benefit from intervention, and those who did not. The only positive finding was that a peripheral renin concentration lower than 8 mlU/l predicted no effect of intervention, which might lead to the exclusion of 11% of the patients before entering the diagnostic programme. We conclude that the RVRS demands a very restrictive referral pattern if it should be of prognostic value for the blood pressure outcome after intervention. No indices of lateralised renin concentrations proved high predictive value. However, a peripheral renin concentration low in the normal range seems useful as an indicator of no benefit from intervention.

The distinct methods by which manganese and iron regulate the Nramp transporters in yeast

The bakers yeast Saccharomyces cerevisiae expresses three Smf metal transport proteins that are differentially regulated by metal ions. Smf1p and Smf2p are regulated at the post-translational level by manganese, whereas Smf3p is regulated by iron through a mechanism that, up until now, was unknown. Through promoter and protein-domain swapping experiments, we now demonstrate that the manganese regulation of Smf1p involves an internal protein-coding region that is separate from the N-terminal domain of this transporter. By comparison, iron regulation of Smf3p involves the upstream non-coding region of the gene. Using SMF3-lacZ reporter constructs, we identified two distinct regions of the SMF3 promoter that contribute to iron regulation: (1) approx. nt -435 to -350 that contain dual consensus recognition sites for the Aft1 iron transcription factor; and (2) nt -348 to -247 that do not contain obvious Aft1 binding sites. The -348 to -247 region by itself can confer strong iron regulation to the heterologous CYC1 core promoter, and therefore harbours a putative upstream activating sequence for iron. Iron regulation of SMF3 was dramatically reduced, but not completely eliminated, in strains lacking both the AFT1 and AFT2 iron regulatory factors. Together with the promoter mapping studies, these results suggest that both Aft-dependent and Aft-independent pathways may contribute to iron regulation of SMF3.

A fraction of yeast Cu,Zn-superoxide dismutase and its metallochaperone, CCS, localize to the intermembrane space of mitochondria. A physiological role for SOD1 in guarding against mitochondrial oxidative damage

Cu,Zn-superoxide dismutase (SOD1) is an abundant, largely cytosolic enzyme that scavenges superoxide anions. The biological role of SOD1 is somewhat controversial because superoxide is thought to arise largely from the mitochondria where a second SOD (manganese SOD) already resides. Using bakers' yeast as a model, we demonstrate that Cu,Zn-SOD1 helps protect mitochondria from oxidative damage, as sod1Delta mutants show elevated protein carbonyls in this organelle. In accordance with this connection to mitochondria, a fraction of active SOD1 localizes within the intermembrane space (IMS) of mitochondria together with its copper chaperone, CCS. Neither CCS nor SOD1 contains typical N-terminal presequences for mitochondrial uptake; however, the mitochondrial accumulation of SOD1 is strongly influenced by CCS. When CCS synthesis is repressed, mitochondrial SOD1 is of low abundance, and conversely IMS SOD1 is very high when CCS is largely mitochondrial. The mitochondrial form of SOD1 is indeed protective against oxidative damage because yeast cells enriched for IMS SOD1 exhibit prolonged survival in the stationary phase, an established marker of mitochondrial oxidative stress. Cu,Zn-SOD1 in the mitochondria appears important for reactive oxygen physiology and may have critical implications for SOD1 mutations linked to the fatal neurodegenerative disorder, amyotrophic lateral sclerosis.

Effect of the two conserved prolines of human growth inhibitory factor (metallothionein-3) on its biological activity and structure fluctuation: comparison with a mutant protein

Human neuronal growth inhibitory factor, a metalloprotein classified as metallothionein-3 (MT-3), impairs the survival and the neurite formation of cultured neurons. In these studies the double P7S/P9A mutant (mutMT-3) and single mutants P7S and P9A of human Zn(7)-MT-3 were generated, and their effects on the biological activity and the structure of the protein were examined. The biological results clearly established the necessity of both proline residues for the inhibitory activity, as even single mutants were found to be inactive. Using electronic absorption, circular dichroism (CD), magnetic CD (MCD), and (113)Cd NMR spectroscopy, the structural features of the metal-thiolate clusters in the double mutant Cd(7)-mutMT-3 were investigated and compared with those of wild-type Cd(7)-MT-3 [Faller, P., Hasler, D. W., Zerbe, O., Klauser, S., Winge, D. R., and Vasák, M. (1999) Biochemistry 38, 10158] and the well characterized Cd(7)-MT-2a from rabbit liver. Similarly to (113)Cd(7)-MT-3 the (113)Cd NMR spectrum of (113)Cd(7)-mutMT-3 at 298 K revealed four major and three minor resonances (approximately 20% of the major ones) between 590 and 680 ppm, originating from a Cd(4)S(11) cluster in the alpha-domain and a Cd(3)S(9) cluster in the beta-domain, respectively. Due to the presence of dynamic processes in the structure of MT-3 and mutMT-3, all resonances showed the absence of resolved homonuclear [(113)Cd-(113)Cd] couplings and large apparent line widths (between 140 and 350 Hz). However, whereas in (113)Cd(7)-mutMT-3 the temperature rise to 323 K resulted in a major recovery of the originally NMR nondetectable population of the Cd(3)S(9) cluster resonances, no such temperature effect was observed in (113)Cd(7)-MT-3. To account for the observed NMR features, a dynamic structural model for the beta-domain is proposed, which involves a folded and a partially unfolded state. It is suggested that in the partially unfolded state a slow cis/trans isomerization of Cys-Pro(7) or Cys-Pro(9) amide bonds in (113)Cd(7)-MT-3 takes place and that this process represents a rate-limiting step in a correct domain refolding. In addition, closely similar apparent stability constants of human MT-3, mutMT-3, and rabbit MT-2a with Cd(II) and Zn(II) ions were found. These results suggest that specific structural features dictated by the repetitive (Cys-Pro)(2) sequence in the beta-domain of MT-3 and not its altered metal binding affinity compared to MT-1/MT-2 isoforms are responsible for the biological activity of this protein.

A dual role for zinc fingers in both DNA binding and zinc sensing by the Zap1 transcriptional activator

The Zap1 transcriptional activator of Saccharomyces cerevisiae controls zinc homeostasis. Zap1 induces target gene expression in zinc-limited cells and is repressed by high zinc. One such target gene is ZAP1 itself. In this report, we examine how zinc regulates Zap1 function. First, we show that transcriptional autoregulation of Zap1 is a minor component of zinc responsiveness; most regulation of Zap1 activity occurs post-translationally. Secondly, nuclear localization of Zap1 does not change in response to zinc, suggesting that zinc regulates DNA binding and/or activation domain function. To understand how Zap1 responds to zinc, we performed a functional dissection of the protein. Zap1 contains two activation domains. DNA-binding activity is conferred by five C-terminal C(2)H(2) zinc fingers and each finger is required for high-affinity DNA binding. The zinc-responsive domain of Zap1 also maps to the C-terminal zinc fingers. Furthermore, mutations that disrupt some of these fingers cause constitutive activity of a bifunctional Gal4 DNA-binding domain-Zap1 fusion protein. These results demonstrate a novel function of Zap1 zinc fingers in zinc sensing as well as DNA binding.

Role of Saccharomyces cerevisiae ISA1 and ISA2 in iron homeostasis

The budding yeast Saccharomyces cerevisiae contains two homologues of bacterial IscA proteins, designated Isa1p and Isa2p. Bacterial IscA is a product of the isc (iron-sulfur cluster) operon and has been suggested to participate in Fe-S cluster formation or repair. To test the function of yeast Isa1p and Isa2p, single or combinatorial disruptions were introduced in ISA1 and ISA2. The resultant isaDelta mutants were viable but exhibited a dependency on lysine and glutamate for growth and a respiratory deficiency due to an accumulation of mutations in mitochondrial DNA. As with other yeast genes proposed to function in Fe-S cluster assembly, mitochondrial iron concentration was significantly elevated in the isa mutants, and the activities of the Fe-S cluster-containing enzymes aconitase and succinate dehydrogenase were dramatically reduced. An inspection of Isa-like proteins from bacteria to mammals revealed three invariant cysteine residues, which in the case of Isa1p and Isa2p are essential for function and may be involved in iron binding. As predicted, Isa1p is targeted to the mitochondrial matrix. However, Isa2p is present within the intermembrane space of the mitochondria. Our deletion analyses revealed that Isa2p harbors a bipartite N-terminal leader sequence containing a mitochondrial import signal linked to a second sequence that targets Isa2p to the intermembrane space. Both signals are needed for Isa2p function. A model for the nonredundant roles of Isa1p and Isa2p in delivering iron to sites of the Fe-S cluster assembly is discussed.

The yeast transcription factor Mac1 binds to DNA in a modular fashion

Mac1 is a metalloregulatory protein that regulates expression of the high affinity copper transport system in the yeast Saccharomyces cerevisiae. Under conditions of high copper concentration, Mac1 represses transcription of genes coding for copper transport proteins. Mac1 binds to DNA sequences called copper response elements (CuREs), which have the consensus sequence 5'-TTTGC(T/G)C(A/G)-3'. Mac1 contains two zinc binding sites, a copper binding site, and the sequence motif RGRP, which has been found in other proteins to mediate binding to the minor groove of A/T-rich sequences in DNA. We have used hydroxyl radical footprinting, missing nucleoside, and methylation interference experiments to investigate the structure of the complex of the DNA binding domain of Mac1 (called here Mac1(t)) with the two CuRE sites found in the yeast CTR1 promoter. We conclude from these experiments that Mac1(t) binds in a modular fashion to DNA, with its RGRP AT-hook motif interacting with the TTT sequence at the 5' end of the CTR1 CuRE site, and with another DNA-binding module(s) binding in the adjacent major groove in the GCTCA sequence.