Purification and characterization of the XPF-ERCC1 complex of human DNA repair excision nuclease

A complex, which consists of ERCC1 (38 kDa) and a 112-kDa protein, was purified from HeLa cells to homogeneity. This complex complemented the nucleotide excision repair defects of rodent ERCC-1, ERCC-4, and human XP-F mutant cell-free extracts, indicating that the 112-kDa protein is XPF/ERCC4 and providing direct biochemical evidence that XPF and ERCC4 are identical. The XPF/ERCC4-ERCC1 complex has an endonuclease activity with preference for single-stranded DNA and a single-stranded region of duplex DNA with a "bubble" structure. This complex also nicks supercoiled DNA weakly, and this nicking activity is stimulated by human replication protein A when the DNA contains UV damage.

Human DNA repair excision nuclease. Analysis of the roles of the subunits involved in dual incisions by using anti-XPG and anti-ERCC1 antibodies

Human DNA repair excision nuclease removes DNA damage by incising on both sides of the lesion in a precise manner. The activity requires participation of 16-17 polypeptides. Of these, the XPF.ERCC1 complex and XPG were predicted to carry the nuclease active sites based on studies with the recombinant proteins and the yeast homologs of these proteins. Furthermore, recent work with model (undamaged) substrates have led to predictions of the roles of these proteins in incising 5' or 3' to the lesion. We have used damaged DNA substrates and antibodies to XPG and ERCC1 to test these predictions. Our results reveal that anti-XPG antibodies change the site of 3' incision and at high concentration inhibit the 3' incision without significantly affecting the 5' incision, indicating that XPG makes the 3' incision and further that under this condition 5' incision can occur without 3' incision. In contrast, anti-ERCC1 antibodies inhibit both the 3' and 5' incisions. Using a defined system for excision repair we also demonstrate that the 3' incision can occur without the 5' incision, leading us to conclude that under certain conditions the two incisions can occur independently.

The mouse 3 beta-hydroxysteroid dehydrogenase multigene family includes two functionally distinct groups of proteins

The enzyme 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) plays an essential role in the biosynthesis of all steroid hormones. We previously reported the isolation, characterization, and tissue-specific expression of four distinct but highly homologous 3 beta HSD cDNAs (forms I, II, III, and IV). Enzymatic characterization of three of these isoforms demonstrated that mouse 3 beta HSD I and III function as dehydrogenase/isomerases, but 3 beta HSD IV functions exclusively as a 3-ketosteroid reductase. We now report the isolation and characterization of an additional distinct mouse 3 beta HSD cDNA, 3 beta HSD V, which is expressed in the liver of male mice beginning in late puberty. Similar to 3 beta HSD IV, 3 beta HSD V functions exclusively as a 3-ketosteroid reductase converting an active androgen, dihydrotestosterone (DHT), into an inactive androgen, 5 alpha-androstane-3 beta,17 beta-diol. Expressed 3 beta HSD V, however, exhibits a considerably lower apparent Michaelis-Menten constant (Km) value for DHT than 3 beta HSD IV (0.47 microM vs. 2.2 microM, respectively). The complete predicted amino acid sequence of 3 beta HSD II is also reported. The predicted amino acid sequence of mouse 3 beta HSD V reveals that this new form is more closely related to the 3-ketosteroid reductases, mouse 3 beta HSD IV and rat III (93 and 84% identity, respectively), than to the other rodent isoforms that share less than 75% identity.(ABSTRACT TRUNCATED AT 250 WORDS)

MK-801 alters the GABAA receptor complex and potentiates flurazepam's antiseizure efficacy

MK-801 is an uncompetitive allosteric antagonist that interferes with glutamate-gated calcium ion conductance through the NMDA receptor-associated ionophore. In an outbred strain of mouse, MK-801 elicits episodes of explosive "popping" behaviors that may serve as a preclinical screening paradigm for novel antipsychotic medications. This investigation examined the effects of MK-801, at doses associated with the elicitation of popping, on the GABAA receptor complex in cerebral cortex, and flurazepam's ability to antagonize electrically precipitated seizures. Twenty four hours after MK-801 administration, there was an increased density of the radiolabeled antagonist-preferring conformation of the central benzodiazepine binding site and a potentiation of flurazepam's antiseizure efficacy. The data show that interference with NMDA receptor-mediated calcium ion conductance is associated with a relatively selective change in the GABAA receptor complex in cerebral cortex, and has functional behavioral consequences. Moreover, the data provide additional evidence for a delicate balance between GABAergic and glutamatergic transmission. Disturbance of this balance can have behavioral consequences for the animal.

Recent studies of the centrifugal blood pump with a magnetically suspended impeller

We have been developing a centrifugal blood pump with a magnetically suspended impeller. To improve pump efficiency, we investigated the pump performances of many kinds of impeller vanes and diffusers, as well as the flow in the gap between the impeller discs and the pump housing. We found the vanes and the diffusers with high pump efficiency; however, high efficiency does not mean low hemolysis. It seems important to prevent generation of small-sized eddies with high shear stress. Hemolysis tests are carried out to find the optimal vane profile and gap clearance. The index of hemolysis and temperature change of our pump is better than those of the Biopump. Short-term in vivo studies show that the layer of white thrombi adheres to the machined rough surface of polycarbonate, which composes the narrow gap (0.2 mm) between the impeller and the pump wall, but a smooth surface coated with silicon prevents adhesion of that layer.

Prognostic significance of ST-segment depression during adenosine perfusion imaging

To determine the significance of ST-segment depression during adenosine perfusion imaging for predicting future cardiac events, 188 patients with interpretable electrocardiograms were assessed 1 to 3 years (mean 21.5 +/- 6.6 months) after adenosine testing. At least 1 mm of ST-segment depression was observed in 32 (17%) patients, with > or = 2 mm of ST-segment depression in 10 (5.3%). Thirty-seven cardiac events occurred during the study period: 2 cardiac deaths, 5 nonfatal myocardial infarctions, 6 admissions for unstable angina, and 24 revascularizations. Univariate predictors of events were a history of congestive heart failure, previous non-Q-wave myocardial infarction, previous coronary angioplasty, use of antianginal medication, ST-segment depression during adenosine infusion (particularly > or = 2 mm), any reversible perfusion defect, transient left ventricular cavity dilation, and the severity of perfusion defects. Multivariate analysis identified > or = 2 mm ST-segment depression as the most significant predictor of cardiac events (relative risk [RR] = 6.5; p = 0.0001). Other independent predictors of events were left ventricular dilation (RR = 3.8; p = 0.002), previous coronary angioplasty (RR = 3.3; p = 0.001), a history of non-Q-wave myocardial infarction (RR = 2.3; p = 0.01), and the presence of any reversible defect (RR = 2.0; p = 0.05). We conclude that ST-segment depression occurs uncommonly during adenosine infusion, but the presence of > or = 2 mm of ST-segment depression is an independent predictor of future cardiac events and provides information in addition to that obtained from clinical variables and the results of adenosine perfusion imaging.

A magnetically suspended centrifugal pump. In vitro and in vivo assessment

To overcome problems derived from the shaft within conventional centrifugal pumps, we have developed a new centrifugal pump, the magnetically suspended centrifugal pump (MSCP), which has no shaft and operates as a bearingless centrifugal pump. The impeller is suspended freely and centrally by magnetic force within the pump. Hemolysis tests were performed in comparison with the Biopump. Index of hemolysis and destruction of platelets were significantly lower in the MSCP than in the Biopump. Animal studies were designed to evaluate the durability and antithrombogenicity of the MSCP. Short-term animal studies were performed using two mongrel dogs. Left heart bypass was established with the MSCP. After 3 hr, the layer of thrombus adherent to the surface of the polycarbonate impeller impaired pumping efficiency. However, using the impeller coated with silicone, no thrombus was observed on the impeller after continuous pumping for 24 hr. In addition, long-term animal studies were performed using two sheep. Left heart bypass was established with the MSCP containing an impeller coated with silicone. In one sheep, the MSCP ran for 14 days without problems in pumping performance and showed no thrombus within the pump. In the other sheep, the MSCP ran for 15 days, and showed no thrombus on the impeller. During each experiment, plasma free hemoglobin levels were less than 15 mg/dl. The MSCP induced less hemolysis than did the Biopump, and the MSCP containing an impeller coated with silicone demonstrated the potential to run for 14 days without thrombus formation within the pump.

Phosphorylated and unphosphorylated forms of human single-stranded DNA-binding protein are equally active in simian virus 40 DNA replication and in nucleotide excision repair

The trimeric human single-stranded DNA-binding protein (HSSB; also called RP-A) plays an essential role in DNA replication, nucleotide excision repair, and homologous DNA recombination. The p34 subunit of HSSB is phosphorylated at the G1/S boundary of the cell cycle or upon exposure of cells to DNA damage-inducing agents including ionizing and UV radiation. We have previously shown that the phosphorylation of p34 is catalyzed by both cyclin-dependent kinase-cyclin A complex and DNA-dependent protein kinase. In this study, we investigated the effect of phosphorylation of p34 by these kinases on the replication and repair function of HSSB. We observed no significant difference with the unphosphorylated and phosphorylated forms of HSSB in the simian virus 40 DNA replication or nucleotide excision repair systems reconstituted with purified proteins. The phosphorylation status of the p34 subunit of HSSB was unchanged during the reactions. We suggest that the phosphorylated HSSB has no direct effect on the basic mechanism of DNA replication and nucleotide excision repair reactions in vitro, although we cannot exclude a role of p34 phosphorylation in modulating HSSB function in vivo through a yet poorly understood control pathway in the cellular response to DNA damage and replication.

ABT-538 is a potent inhibitor of human immunodeficiency virus protease and has high oral bioavailability in humans

Examination of the structural basis for antiviral activity, oral pharmacokinetics, and hepatic metabolism among a series of symmetry-based inhibitors of the human immunodeficiency virus (HIV) protease led to the discovery of ABT-538, a promising experimental drug for the therapeutic intervention in acquired immunodeficiency syndrome (AIDS). ABT-538 exhibited potent in vitro activity against laboratory and clinical strains of HIV-1 [50% effective concentration (EC50) = 0.022-0.13 microM] and HIV-2 (EC50 = 0.16 microM). Following a single 10-mg/kg oral dose, plasma concentrations in rat, dog, and monkey exceeded the in vitro antiviral EC50 for > 12 h. In human trials, a single 400-mg dose of ABT-538 displayed a prolonged absorption profile and achieved a peak plasma concentration in excess of 5 micrograms/ml. These findings demonstrate that high oral bioavailability can be achieved in humans with peptidomimetic inhibitors of HIV protease.

Benzodiazepines and peptides stimulate pregnenolone synthesis in brain mitochondria

Mitochondria isolated from rat brain were found to cleave cholesterol to produce pregnenolone, the precursor for hormonal steroids, at a mean rate of 21.0 pmol pregnenolone.mg protein-1.min-1. This rate-limiting step in steroidogenesis was significantly stimulated by PK 11195 (1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide) and Ro5 4864 (4'-chlorodiazepam), ligands which bind to peripheral benzodiazepine receptors with high affinity. Low-affinity ligands for the peripheral benzodiazepine receptor such as Ro15 1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5 alpha][1,4] benzo-3-carboxylate) and clonazepam had no significant effect on the rate of pregnenolone synthesis. Furthermore, the rank order of potency of these compounds as inhibitors of [3H]Ro5 4864 binding was identical to the rank order for steroid production. Since the 86-amino acid peptide diazepam binding inhibitor is also thought to bind to the peripheral benzodiazepine receptor, four fragments of this peptide, a random sequence and steroidogenesis activator peptide were also evaluated for their ability to interact with peripheral benzodiazepine receptors and to stimulate steroidogenesis in rat brain mitochondria. Steroidogenesis activator peptide and two fragments of diazepam binding inhibitor significantly stimulated pregnenolone biosynthesis. In contrast to the peripheral benzodiazepine receptor ligands, no correlation between peptide potency in displacing [3H]Ro5 4864 binding and steroidogenesis was observed.

The general transcription-repair factor TFIIH is recruited to the excision repair complex by the XPA protein independent of the TFIIE transcription factor

Recent studies have revealed that the general transcription factor TFIIH is also a general excision repair factor which, along with several other proteins, is required for transcription-independent excision reaction. As a general transcription factor, TFIIH is recruited to RNA polymerase II-promoter complex by another general transcription factor called TFIIE. We were interested in knowing whether TFIIE is also involved in recruiting TFIIH to the excision repair complex. We found that cell-free extract depleted of TFIIE carried out excision repair at a normal rate, leading us to conclude that TFIIE is not involved in recruiting TFIIH to the damage site and has no role in general excision repair. In contrast, the human damage recognition protein XPA specifically binds to TFIIH and apparently recruits it to the damage site. The carboxyl-terminal half of XPA is responsible for specific interaction with TFIIH. The C261S/C264S mutant of XPA bound the ERCC1-XPF complex normally, but failed to bind TFIIH and failed to complement an XP-A mutant cell-free extract indicating that the XPA-TFIIH interaction is essential to effecting the excision reaction. Interestingly, XPA also binds to the p34 subunit of TFIIE specifically and in competition with the p56 subunit of TFIIE. This latter interaction has no apparent role in general excision repair but may be relevant in the transcription-coupled repair reaction.

Delayed radioiodine organification in Plummer's disease

Hyperfunctioning thyroid adenomas causing thyrotoxicosis (Plummer's disease) is not an uncommon cause of hyperthyroidism in the elderly. Most commonly, the adenoma appears as a so-called "hot" nodule on thyroid scintigraphy causing suppression (i.e., nonvisualization) of the remainder of the gland. This report describes a case of Plummer's disease in an elderly patient in whom the toxic nodule primarily responsible for causing the hyperthyroidism became scintigraphically apparent at 96 hours after I-131 therapeutic ablation.

Tc-99m MIBI uptake secondary to pulmonary interstitial fibrosis in progressive systemic sclerosis

Pulmonary uptake of Tc-99m MIBI in a patient with progressive systemic sclerosis (PSS, diffuse scleroderma) is described. Nonspecific alveolitis, active interstitial fibrosis pulmonary hypertension, and specific uptake by the fibroblasts in patients with PSS are possible mechanisms of Tc-99 MIBI uptake observed.

67Gallium scans in Löfgren's syndrome

Comparison of 67Gallium scans of head and neck showed no significant difference in intensity of uptake between patients with Löfgren's syndrome and sarcoidosis patients with similar chest x rays having other modes of onset. Uptake was the same in the 12 white and 18 black patients studied. Thus, the increased bronchoaveolar lavage lymphocytosis which has been shown to be a feature of Löfgren's syndrome is not paralleled by gallium uptake. Gallium scores had no predictive value regarding outcome showing no significant difference between 13 patients who recovered within a year and 15 patients who developed chronic disease. The outcome was more favorable in white patients and in those whose onset was with Löfgren's syndrome.

Reconstitution of human DNA repair excision nuclease in a highly defined system

Xeroderma pigmentosum is a hereditary disease caused by defective DNA repair. Somatic cell genetics and biochemical studies with cell-free extracts indicate that at least 16 polypeptides are required to carry out the repair reaction proper, i.e. the removal of the lesion from the DNA by the dual incisions of the damaged strand. To find out if these proteins are necessary and sufficient for excision repair, they were obtained at a high level of purity in five fractions. The mixture of these five fractions reconstituted the excision nuclease (excinuclease) activity. Using the reconstituted excinuclease, we found that the excised fragment remains associated with the post-incision DNA-protein complex, suggesting that accessory proteins are needed to release the excised oligomer.

Successful engraftment using allogeneic peripheral blood progenitor cells in a patient with primary bone marrow graft failure

G-CSF-mobilized peripheral blood progenitor cells (PBPC) were utilized in a patient who failed to engraft after an unmanipulated HLA-matched allogeneic bone marrow transplant. Marrow engraftment occurred after repeated conditioning with high-dose cyclophosphamide and PBPC infusion. Severe graft-versus-host disease (GVHD) developed shortly after marrow engraftment. The role of PBPC in allogeneic transplant, the associated potential risk of GVHD, and the necessity of reconditioning before stem cell reinfusion are discussed.

False-positive reversible perfusion defect during dobutamine-thallium imaging in left bundle branch block

In the presence of pre-existing left bundle branch block (LBBB) exercise stress thallium scans have been associated with false-positive septal and apical perfusion abnormalities. Recent reports have documented a lower incidence of false-positive septal perfusion defects when pharmacologic agents such as dipyridamole or adenosine are utilized in patients with LBBB. Dobutamine, a synthetic catecholamine, is being used with increasing frequency in combination with perfusion agents for the diagnosis of coronary artery disease in patients unable to achieve an adequate exercise workload. Because the positive inotropic and chronotropic actions of doubtamine are similar to the physiologic effects of treadmill exercise, it is conceivable that false-positive perfusion abnormalities will be observed in patients with pre-existing LBBB undergoing dobutamine perfusion imaging. We describe a patient with underlying LBBB who underwent dobutamine thallium imaging which revealed septal and periapical defects. Subsequent coronary angiography showed these abnormalities to be false-positive. It is concluded that septal and periapical perfusion abnormalities during dobutamine thallium imaging may be false-positive and should be interpreted cautiously.

Recruitment with high physiological doses of estradiol preceding chemotherapy: flow cytometric and therapeutic results in women with locally advanced breast cancers--a Southwest Oncology Group study

One theoretical method of increasing chemotherapeutic efficacy in breast cancer is to temporarily increase the number of tumor cells in cycle through hormonal recruitment prior to initiation of chemotherapy. In an effort to determine when and if this could be reliably accomplished, 50 women with locally advanced and/or metastatic breast cancer with known estrogen receptor (ER) status were entered into a serial breast biopsy study designed to measure increases in S-phase fraction (SPF) and proliferative index (PI; S + G2 + M) following administration of a high physiological dose of estrogen via estradiol vaginal suppositories prior to chemotherapy. Blood levels of estradiol were maintained in a range (0.5-5 nM) known to increase SPF in vitro. Compliance with suppository administration was monitored by serial blood sampling. Tumors were sampled at 0, 24, 48, 72, and/or 96 h. Thirty-one ER-positive and 9 ER-negative women had evaluable baseline biopsies and at least 1 subsequent biopsy. An increase was seen for SPF in 20 (69%) and for PI in 23 (79%) of 29 ER-positive patients at 48 h after estrogen initiation (95% confidence intervals, 49-85% for SPF and 60-92% for PI); similar increases were seen at 72 h. Median baseline SPF and PI values in ER-positive patients for whom increases were noted at 48 h were 6.2 and 8.5%, respectively. The median relative increases in these patients were 170 and 100%, respectively, at 48 h. The increases observed at 24 h in 4 (SPF) and 6 (PI) of the 9 ER-negative patients could have occurred by chance alone. Twenty-five of the 28 locally advanced (T4 and/or N2-3) patients achieved a complete response during combined modality treatment (estradiol-chemotherapy, mastectomy, and radiation). At a minimum follow-up time of 42 months, estimated 5-year progression-free and overall survivals are 30 and 49%, respectively, with a median time to progression of 35 months. Twenty-two women had metastatic disease (19 also had locally advanced disease). Thirteen had a complete or partial response, with a median duration of 12 months. Median progression-free and over-all survival times for all metastatic patients are 4 and 17 months, respectively. Estimated 5-year survival for metastatic disease patients is 27%. A high physiological dose of estrogen administered to patients with locally advanced ER-positive tumors can reliably increase the tumor SPF and PI within 48 h.(ABSTRACT TRUNCATED AT 400 WORDS)