ATHLET extensions for the simulation of supercritical carbon dioxide driven power cycles

The Fukushima accident reveals the need for additional safety systems for nuclear power plants. One promising option is the supercritical carbon-dioxide (sCO2) heat removal system, which consists of a simple Brayton cycle. This study provides an overview of the extensions and validation of the thermal-hydraulic system code ATHLET for the simulation of sCO2 power cycles, especially with regard to the sCO2 heat removal system. The properties of CO2, heat transfer and pressure drop correlations, as well as compact heat exchanger and turbomachinery modelling are considered.

Tolerogenic dendritic cells generated with dexamethasone and vitamin D3 regulate rheumatoid arthritis CD4+ T cells partly via transforming growth factor-β1

Tolerogenic dendritic cells (tolDC) are a new immunotherapeutic tool for the treatment of rheumatoid arthritis (RA) and other autoimmune disorders. We have established a method to generate stable tolDC by pharmacological modulation of human monocyte-derived DC. These tolDC exert potent pro-tolerogenic actions on CD4⁺ T cells. Lack of interleukin (IL)-12p70 production is a key immunoregulatory attribute of tolDC but does not explain their action fully. Here we show that tolDC express transforming growth factor (TGF)-β1 at both mRNA and protein levels, and that expression of this immunoregulatory cytokine is significantly higher in tolDC than in mature monocyte-derived DC. By inhibiting TGF-β1 signalling we demonstrate that tolDC regulate CD4⁺ T cell responses in a manner that is at least partly dependent upon this cytokine. Crucially, we also show that while there is no significant difference in expression of TGF-βRII on CD4⁺ T cells from RA patients and healthy controls, RA patient CD4⁺ T cells are measurably less responsive to TGF-β1 than healthy control CD4⁺ T cells [reduced TGF-β-induced mothers against decapentaplegic homologue (Smad)2/3 phosphorylation, forkhead box protein 3 (FoxP3) expression and suppression of (IFN)-γ secretion]. However, CD4⁺ T cells from RA patients can, nonetheless, be regulated efficiently by tolDC in a TGF-β1-dependent manner. This work is important for the design and development of future studies investigating the potential use of tolDC as a novel immunotherapy for the treatment of RA.

Lateralisation in agonistic encounters: do mirror tests reflect aggressive behaviour? A study on a West African cichlid

In this study, population level lateralisation and the suitability of mirror tests as a test of natural aggressive behaviour in male rainbow kribs Pelvicachromis pulcher was investigated. Aggressive behaviour in live agonistic trials correlated positively with behaviours towards a mirror image and no visual lateralisation was detected.

Organ Specific Storage of Dietary Pyrrolizidine Alkaloids in the Arctiid Moth Creatonotos transiens

Larvae of the arctiid moth Creatonotos transiens obtained each 5 mg of heliotrine, a pyrrolizidine alkaloid, via an artificial diet. 7 S-H eliotrine is converted into its enantiomer, 7 R1-heliotrine, and some minor metabolites, such as callimorphine. 7 S- and 7 R-heliotrine are present in the insect predominantly (more than 97%) as their N-oxides. The distribution of heliotrine in the organs and tissues of larvae, prepupae, pupae and imagines was analyzed by capillary gas-liquid chromatography. A large proportion of the alkaloid is stored in the integument of all developmental stages, where it probably serves as a chemical defence compound against predators. Female imagines had transferred substantial amounts of heliotrine to their ovaries and subsequently to their eggs; males partly directed it to their pheromone biosynthesis.

Electrochemical investigation of covalently post-synthetic modified SURGEL coatings

Thiol–yne click chemistry post synthesis modification (PSM) is used to further functionalize a fully organic porous polymer coating (SURGEL). By cyclic voltammetry the resulting electrochemical properties are addressed. The Nernstian diffusion limited process observed in the presence of ferrocene as electrolyte is explained in terms of a high permeability of the SURGELs for ferrocene after PSM.

The RecX protein interacts with the RecA protein and modulates its activity in Herbaspirillum seropedicae

DNA repair is crucial to the survival of all organisms. The bacterial RecA protein is a central component in the SOS response and in recombinational and SOS DNA repairs. The RecX protein has been characterized as a negative modulator of RecA activity in many bacteria. The recA and recX genes of Herbaspirillum seropedicae constitute a single operon, and evidence suggests that RecX participates in SOS repair. In the present study, we show that the H. seropedicae RecX protein (RecX Hs) can interact with the H. seropedicaeRecA protein (RecA Hs) and that RecA Hs possesses ATP binding, ATP hydrolyzing and DNA strand exchange activities. RecX Hs inhibited 90% of the RecA Hs DNA strand exchange activity even when present in a 50-fold lower molar concentration than RecA Hs. RecA Hs ATP binding was not affected by the addition of RecX, but the ATPase activity was reduced. When RecX Hs was present before the formation of RecA filaments (RecA-ssDNA), inhibition of ATPase activity was substantially reduced and excess ssDNA also partially suppressed this inhibition. The results suggest that the RecX Hs protein negatively modulates the RecA Hs activities by protein-protein interactions and also by DNA-protein interactions.

Physiologic and pharmacologic considerations for hypothermia therapy in neonates

With mounting evidence that hypothermia is neuroprotective in newborns with hypoxic-ischemic encephalopathy (HIE), an increasing number of centers are offering this therapy. Hypothermia is associated with a wide range of physiologic changes affecting every organ system, and awareness of these effects is essential for optimum patient management. Lowering the core temperature also alters pharmacokinetic and pharmacodynamic properties of medications commonly used in asphyxiated neonates, necessitating close attention to drug efficacy and side effects. Rewarming introduces additional risks and challenges as the hypothermia-associated physiologic and pharmacologic changes are reversed. In this review we provide an organ system-based assessment of physiologic changes associated with hypothermia. We also summarize evidence from randomized controlled trials showing lack of serious adverse effects of moderate hypothermia therapy in term and near-term newborns with moderate-to-severe HIE. Finally, we review the effects of hypothermia on drug metabolism and clearance based on studies in animal models and human adults, and limited data from neonates.

The evolution of the phage shock protein response system: interplay between protein function, genomic organization, and system function

Sensing the environment and responding appropriately to it are key capabilities for the survival of an organism. All extant organisms must have evolved suitable sensors, signaling systems, and response mechanisms allowing them to survive under the conditions they are likely to encounter. Here, we investigate in detail the evolutionary history of one such system: The phage shock protein (Psp) stress response system is an important part of the stress response machinery in many bacteria, including Escherichia coli K12.

Here, we use a systematic analysis of the genes that make up and regulate the Psp system in E. coli in order to elucidate the evolutionary history of the system. We compare gene sharing, sequence evolution, and conservation of protein-coding as well as noncoding DNA sequences and link these to comparative analyses of genome/operon organization across 698 bacterial genomes. Finally, we evaluate experimentally the biological advantage/disadvantage of a simplified version of the Psp system under different oxygen-related environments.

Our results suggest that the Psp system evolved around a core response mechanism by gradually co-opting genes into the system to provide more nuanced sensory, signaling, and effector functionalities. We find that recruitment of new genes into the response machinery is closely linked to incorporation of these genes into a psp operon as is seen in E. coli, which contains the bulk of genes involved in the response. The organization of this operon allows for surprising levels of additional transcriptional control and flexibility. The results discussed here suggest that the components of such signaling systems will only be evolutionarily conserved if the overall functionality of the system can be maintained.

YB-1 Mediates a Crosstalk between ERα and TGFβ Signaling in Breast Cancer Cells

The multifunctional Y-box binding protein-1 (YB-1) belongs to the highly conserved family of cold shock proteins being involved in transcriptional/translational regulation, DNA repair as well as stress response. Additionally, it is highly expressed in many malignant tissues which seems to correlate with a high proliferation level, drug resistance and a poor prognosis in a variety of tumors including breast cancer.Using quantitative immunohistochemistry we now confirm the previously described negative prognostic impact of YB-1 on survival in a clinical study with tumor samples from 199 breast cancer patients (p=0.0146; median follow up 79 months).Treatment of the estrogen receptor α (ERα) positive human breast cancer cell line MCF-7 with antiestrogens (4-hydroxytamoxifen, faslodex) resulted in a time and dose dependent decrease of YB-1 expression on the RNA- as well as on the protein level. In contrast, antiestrogen treatment of the ERα negative cell line MDA-MB-231 does not have any effect indicating that the antiestrogen effect on YB-1 is mediated by ERα. We have already demonstrated that the action of all antiestrogens is at least partially mediated by transforming growth factor β (TGFβ) (e.g. Breast Cancer Res. Treat. 107: 15-24, 2008). Using TGFβ-responsive reporter gene assays we now show that overexpression of YB-1 in MCF-7 cells enhances the induction of p3TPlux activity by TGFβ suggesting a crosstalk between YB-1 and TGFβ signaling pathways. Moreover, YB-1 also increases the antiestrogen induction of the TGFβ2-mRNA level coming along with a YB-1 regulated enhancement of the antiestrogen effect on cell growth.Very recent findings of our group point towards a ligand-independent influence of ERα on TGFβ signaling (Breast Cancer Res. Treat., in press). Due to the antiestrogen regulation of YB-1 via ERα and its crosstalk with the TGFβ pathway, the potential role of YB-1 as a mediator of the interaction between ERα and TGFβ signaling was analyzed. Performing pull-down assays with recombinant GST-ERα and whole cell lysates of MCF-7 cells confirms a protein-protein interaction between YB-1 and ERα. The physiological relevance of this interaction could be demonstrated, as the TGFβ-induced p3TPlux activity is clearly modulated by both, YB-1 and ERα.In conclusion, we present evidence that YB-1 and TGFβ signaling are functionally linked in MCF-7 cells. Combined with the detection of a physical interaction between YB-1 and ERα, our findings shed new light on a potential role of YB-1 as a part of the mechanism responsible for switching TGFβ from its anti-proliferative role in early tumor stages to tumor promoting effects in late-stage disease, most likely via a YB-1 regulated shift of TGFβ-signaling to pro-invasive pathways. This would also explain why high levels of YB-1 correlate with a poor prognosis in breast cancer patients.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4172.

Identification of claudin-4 as a marker highly overexpressed in both primary and metastatic prostate cancer

In the quest for markers of expression and progression for prostate cancer (PCa), the majority of studies have focussed on molecular data exclusively from primary tumours. Although expression in metastases is inferred, a lack of correlation with secondary tumours potentially limits their applicability diagnostically and therapeutically. Molecular targets were identified by examining expression profiles of prostate cell lines using cDNA microarrays. Those genes identified were verified on PCa cell lines and tumour samples from both primary and secondary tumours using real-time RT–PCR, western blotting and immunohistochemistry. Claudin-4, coding for an integral membrane cell-junction protein, was the most significantly (P<0.00001) upregulated marker in both primary and metastatic tumour specimens compared with benign prostatic hyperplasia at both RNA and protein levels. In primary tumours, claudin-4 was more highly expressed in lower grade (Gleason 6) lesions than in higher grade (Gleason ⩾7) cancers. Expression was prominent throughout metastases from a variety of secondary sites in fresh-frozen and formalin-fixed specimens from both androgen-intact and androgen-suppressed patients. As a result of its prominent expression in both primary and secondary PCas, together with its established role as a receptor for Clostridium perfringens enterotoxin, claudin-4 may be useful as a potential marker and therapeutic target for PCa metastases.

Compensatory and long-range changes in picosecond-nanosecond main-chain dynamics upon complex formation: 15N relaxation analysis of the free and bound states of the ubiquitin-like domain of human plexin-B1 and the small GTPase Rac1

The formation of a complex between Rac1 and the cytoplasmic domain of plexin-B1 is one of the first documented cases of a direct interaction between a small guanosine 5'-triphosphatase (GTPase) and a transmembrane receptor. Structural studies have begun to elucidate the role of this interaction for the signal transduction mechanism of plexins. Mapping of the Rac1 GTPase surface that contacts the Rho GTPase binding domain of plexin-B1 by solution NMR spectroscopy confirms the plexin domain as a GTPase effector protein. Regions neighboring the GTPase switch I and II regions are also involved in the interaction and there is considerable interest to examine the changes in protein dynamics that take place upon complex formation. Here we present main-chain nitrogen-15 relaxation measurements for the unbound proteins as well as for the Rho GTPase binding domain and Rac1 proteins in their complexed state. Derived order parameters, S2, show that considerable motions are maintained in the bound state of plexin. In fact, some of the changes in S2 on binding appear compensatory, exhibiting decreased as well as increased dynamics. Fluctuations in Rac1, already a largely rigid protein on the picosecond-nanosecond timescale, are overall diminished, but isomerization dynamics in the switch I and II regions of the GTPase are retained in the complex and appear to be propagated to the bound plexin domain. Remarkably, fluctuations in the GTPase are attenuated at sites, including helices alpha6 (the Rho-specific insert helix), alpha7 and alpha8, that are spatially distant from the interaction region with plexin. This effect of binding on long-range dynamics appears to be communicated by hinge sites and by subtle conformational changes in the protein. Similar to recent studies on other systems, we suggest that dynamical protein features are affected by allosteric mechanisms. Altered protein fluctuations are likely to prime the Rho GTPase-plexin complex for interactions with additional binding partners.

Self-assembled monolayers of aromatic selenolates on noble metal substrates

Self-assembled monolayers (SAMs) formed from bis(biphenyl-4-yl) diselenide (BBPDSe) on Au(111) and Ag(111) substrates have been characterized by high-resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared reflection absorption spectroscopy, water contact angle measurements, and scanning tunneling microscopy (STM). BBPDSe was found to form contamination-free, densely packed, and well-ordered biphenyl selenolate (BPSe) SAMs on both Au and Ag. Spectroscopic data suggest very similar packing density, orientational order, and molecular inclination in BPSe/Au and BPSe/Ag. STM data give a similar intermolecular spacing of 5.3 +/- 0.4 A on both Au and Ag but exhibit differences in the exact arrangement of the BPSe molecules on these two substrates, with the (2 square root[3] x square root[3])R30 degrees and (square root[3] x square root[3])R30 degrees unit cells on Au and Ag, respectively. There is strong evidence for adsorbate-mediated substrate restructuring in the case of Au, whereas no clear statement on this issue can be made in the case of Ag. The film quality of the BPSe SAMs is superior to their thiol analogues, which is presumably related to a better ability of the selenolates to adjust the surface lattice of the substrate to the most favorable 2D arrangement of the adsorbate molecules. This suggests that aromatic selenolates represent an attractive alternative to the respective thiols.

Phase II study of gemcitabine and oxaliplatin in patients with recurrent ovarian cancer: an Australian and New Zealand Gynaecological Oncology Group study

Gemcitabine and oxaliplatin have shown single-agent activity in relapsed ovarian cancer. This combination was used to determine response rates, time-to-event efficacy measures, and toxicity in patients with recurrent ovarian cancer. Patients with prior platinum-based chemotherapy who had measurable lesions and/or elevated CA-125 levels were identified as group A (platinum-refractory/platinum-resistant patients) and group B (platinum-sensitive patients). All patients received gemcitabine 1000 mg/m(2) on days 1 and 8 and oxaliplatin 130 mg/m(2) on day 8 every 21 days for up to eight cycles. Seventy-five patients (21 in group A and 54 in group B), with a median age of 58 years (range, 37-78), were enrolled. A median of six cycles (range, 1-8) was administered. By intent-to-treat analysis, 15 patients with measurable disease achieved partial response for an overall best response rate of 20.0% (9.5% in group A and 24.1% in group B). CA-125 response was observed in 48.4% patients (30.0% in group A and 57.1% in group B). Median time to progressive disease was 7.1 months (95% CI, 5.6-9.0 months) with 5.0 months in group A and 8.3 months in group B. Median overall survival was 17.8 months (95% CI, 12.9-21.3 months) with 9.2 months for group A and 20.0 months for group B. Major grade 3/4 toxicities were neutropenia (61.3%), leukopenia (24.0%), nausea (16.0%), and vomiting (22.7%). We conclude that the combination of oxaliplatin and gemcitabine is active in patients with recurrent ovarian cancer, but the regimen is unsatisfactory for further study due to modest response and relatively high toxicity.

Phase II study of carboplatin followed by sequential gemcitabine and paclitaxel as first-line treatment for advanced ovarian cancer

The aim of this exploratory phase II study was to evaluate sequential chemotherapy with carboplatin followed by gemcitabine-paclitaxel combination in chemonaive patients with advanced ovarian cancer. The primary objective was to evaluate time to progressive disease (TTPD); secondary objectives included the evaluation of 1- and 3-year survival, response rates, and toxicity. Following initial debulking surgery or biopsy, patients with FIGO stage IIC-IV disease received four cycles of carboplatin area under the curve (AUC) 6 (day 1) every 21 days, followed by four cycles of gemcitabine 1000 mg/m(2) (days 1 and 8) and paclitaxel 175 mg/m(2) (day 8) every 21 days. A total of 47 patients enrolled, 44 (93.6%) completed the initial four cycles, and 39 patients (82.9%) completed the planned eight cycles. The median and maximum lengths of follow-up were 31.2 and 43.7 months, respectively. Median TTPD was 13.8 months (95% CI, 11.6-21.0 months), and median survival time was 31.2 months (95% CI, 25.2-39.6 months). Survival at 1 and 3 years was 95.7% and 44.2%, respectively. Of the 43 evaluable patients, most (95.3%) of them achieved a CA-125 marker response based on Gynecologic Cancer Intergroup (GCIG) definition. The partial response rate in the seven patients with measurable disease was 46.4%. Myelosuppression was the major toxicity, with grade 3 and 4 neutropenia observed in 76.6% patients and thrombocytopenia in 12.8% patients. The sequential approach of carboplatin followed by gemcitabine-paclitaxel as first-line treatment for patients with ovarian cancer is feasible and well tolerated, and depending upon the findings from other major trials, it may merit further evaluation.

Phase II trial of weekly docetaxel for patients with relapsed ovarian cancer who have previously received paclitaxel—ANZGOG 02-01

OBJECTIVE

To determine the response rate of weekly docetaxel in women with relapsed epithelial ovarian cancer previously treated with paclitaxel and at least one line of platinum-based chemotherapy.

METHODS

In this multi-center phase II trial, 37 patients with relapsed disease were enrolled and treated with weekly docetaxel at 35 mg/m for 5 out of 6 consecutive weeks. Two patient cohorts were considered, those who progressed or relapsed within 4 months (N=7) or at greater than 4 months (N=30) from the time of completing their last course of paclitaxel.

RESULTS

Patients in both cohorts received a median of 2 cycles of treatment (range; 1-4). In evaluable patients, the combined overall response rate, using both CA125 and RECIST response criteria was 18.9% (7/37; 95% CI; 10-34%). The combined overall progression-free survival was 3.1 months (95% CI; 2.5-3.8), and the combined overall survival was 12.3 months (95% CI; 8.2-16.4). Treatment was generally well tolerated with the only grade 4 toxicity being skin toxicity (3%). The most common grade 3 toxicities were fatigue (14%) and watery eyes (8%) with grade 3 neutropenia observed in only 5% of patients.

CONCLUSION

Weekly docetaxel is well tolerated and has activity in patients with relapsed ovarian cancer previously treated with platinum and paclitaxel.

A second paradigm for gene activation in bacteria

Control of gene expression is key to development and adaptation. Using purified transcription components from bacteria, we employ structural and functional studies in an integrative manner to elaborate a detailed description of an obligatory step, the accessing of the DNA template, in gene expression. Our work focuses on a specialized molecular machinery that utilizes ATP hydrolysis to initiate DNA opening and permits a description of how the events triggered by ATP hydrolysis within a transcriptional activator can lead to DNA opening and transcription. The bacterial EBPs (enhancer binding proteins) that belong to the AAA(+) (ATPases associated with various cellular activities) protein family remodel the RNAP (RNA polymerase) holoenzyme containing the sigma(54) factor and convert the initial, transcriptionally silent promoter complex into a transcriptionally proficient open complex using transactions that reflect the use of ATP hydrolysis to establish different functional states of the EBP. A molecular switch within the model EBP we study [called PspF (phage shock protein F)] is evident, and functions to control the exposure of a solvent-accessible flexible loop that engages directly with the initial RNAP promoter complex. The sigma(54) factor then controls the conformational changes in the RNAP required to form the open promoter complex.

Self-assembled monolayers of semifluorinated alkaneselenolates on noble metal substrates

Self-assembled monolayers (SAMs) formed from semifluorinated dialkyldiselenol (CF(3)(CF(2))(5)(CH(2))(2)Se-)(2) (F6H2SeSeH2F6) on polycrystalline Au(111) and Ag(111) were characterized by high-resolution X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, near edge X-ray absorption fine structure spectroscopy, scanning tunneling microscopy, and contact angle measurements. The Se-Se linkage of F6H2SeSeH2F6 was found to be cleaved upon the adsorption, followed by the formation of selenolate-metal bond. The resulting F6H2Se SAMs are well-ordered, densely packed, and contamination-free. The packing density of these films is governed by the bulky fluorocarbon part, which exhibits the expected helical conformation. A noncommensurate hexagonal arrangement of the F6H2Se molecules with an average nearest-neighbor spacing of about 5.8 +/- 0.2 A, close to the van der Waals diameter the fluorocarbon chain, was observed on Au(111). The orientation of the fluorocarbon chains in the F6H2Se SAMs does not depend on the substrate-the average tilt angle of these moieties was estimated to be about 21-22 degrees on both Au and Ag.

Cisplatin and gemcitabine induction chemotherapy followed by concurrent chemoradiotherapy or surgery for locally advanced non-small cell lung cancer

BACKGROUND

We report a study of induction chemotherapy followed by concurrent chemoradiotherapy for stage IIIA/IIIB non-small cell lung cancer.

METHODS

Patients received two cycles of induction chemotherapy with cisplatin 100 mg/m(2) on day 1 and gemcitabine 1000 mg/m(2) on days 1, 8, and 15 of a 28-day cycle. If the disease was resectable [corrected] surgery was followed with two further cycles. If unresectable, patients received cisplatin 100 mg/m(2) day 1, 29 with 5-fluorouracil 1000 mg/m(2) per 24 h continuous infusion for 96 h on days 2-5 and days 30-33 of the radiotherapy administration. Radiation therapy consisted of 63 Gy, 35 fractions, 7 weeks.

RESULTS

Of 48 patients, 40% had a partial response to induction chemotherapy. Four of eleven patients with stage IIIA tumours had resectable disease. The remaining seven patients plus 37 with stage IIIB disease had chemoradiotherapy. Response at the completion of all therapy was 62% (IIIA 73%, IIIB 59%). For all patients the median survival was 15.3 months: 1 year and 3 years, 58% and 25%, respectively. Those with IIIB disease responding to induction chemotherapy had significantly superior survival to those that did not respond (37 months vs 11 months; P = 0.005). This remained significant from a landmark at 8 weeks after the start of treatment (P = 0.01).

CONCLUSION

These results are equivalent to other studies using induction chemotherapy prior to concurrent chemoradiotherapy. Response to induction chemotherapy may have major prognostic significance.

Nucleotide-dependent interactions between a fork junction-RNA polymerase complex and an AAA+ transcriptional activator protein

Enhancer-dependent transcriptional activators that act upon the sigma54 bacterial RNA polymerase holoenzyme belong to the extensive AAA+ superfamily of mechanochemical ATPases. Formation and collapse of the transition state for ATP hydrolysis engenders direct interactions between AAA+ activators and the sigma54 factor, required for RNA polymerase isomerization. A DNA fork junction structure present within closed complexes serves as a nucleation point for the DNA melting seen in open promoter complexes and restricts spontaneous activator-independent RNA polymerase isomerization. We now provide physical evidence showing that the ADP.AlF(x) bound form of the AAA+ domain of the transcriptional activator protein PspF changes interactions between sigma54-RNA polymerase and a DNA fork junction structure present in the closed promoter complex. The results suggest that one functional state of the nucleotide-bound activator serves to alter DNA binding by sigma54 and sigma54-RNA polymerase and appears to drive events that precede DNA opening. Clear evidence for a DNA-interacting activity in the AAA+ domain of PspF was obtained, suggesting that PspF may make a direct contact to the DNA component of a basal promoter complex to promote changes in sigma54-RNA polymerase-DNA interactions that favour open complex formation. We also provide evidence for two distinct closed promoter complexes with differing stabilities.

Mechanochemical ATPases and transcriptional activation

Transcriptional activator proteins that act upon the sigma54-containing form of the bacterial RNA polymerase belong to the extensive AAA+ superfamily of ATPases, members of which are found in all three kingdoms of life and function in diverse cellular processes, often via chaperone-like activities. Formation and collapse of the transition state of ATP for hydrolysis appears to engender the interaction of the activator proteins with sigma54 and leads to the protein structural transitions needed for RNA polymerase to isomerize and engage with the DNA template strand. The common oligomeric structures of AAA+ proteins and the creation of the active site for ATP hydrolysis between protomers suggest that the critical changes in protomer structure required for productive interactions with sigma54-holoenzyme occur as a consequence of sensing the state of the gamma-phosphate of ATP. Depending upon the form of nucleotide bound, different functional states of the activator are created that have distinct substrate and chaperone-like binding activities. In particular, interprotomer ATP interactions rely upon the use of an arginine finger, a situation reminiscent of GTPase-activating proteins.

Antiestrogenic regulation of transforming growth factor beta receptors I and II in human breast cancer cells

To obtain more information about the interactions between antiestrogens and transforming growth factor beta (TGF-beta) signaling, we analyzed the influence of different types of antiestrogens on the expression of TGF-beta receptors I (TbetaRI) and II (TbetaRII). Our results show that antiestrogens selectively induce TbetaRII but not TbetaRI mRNA.

Global disruption of the WASP autoinhibited structure on Cdc42 binding. Ligand displacement as a novel method for monitoring amide hydrogen exchange

The Cdc42 GTPase, a member of the Rho subfamily of Ras proteins, can signal to the cytoskeleton through its effector, the Wiskott-Aldrich syndrome protein (WASP), activation of which results in localized polymerization of new actin filaments. NMR structures of WASP peptide models in the Cdc42-bound and free states suggest that GTPase binding weakens autoinhibitory contacts between the GTPase binding domain (GBD) and the C-terminal actin regulatory (VCA) region of the protein. In the study presented here, amide hydrogen exchange has been used with NMR spectroscopy to directly examine destabilization of the autoinhibited GBD-VCA conformation caused by GTPase binding. A truncated protein, GBD-C, which models autoinhibited WASP, folds into a highly stable conformation with amide exchange protection factors of up to 3 x 10(6). A novel hydrogen exchange labeling-quench strategy, employing a high-affinity ligand to displace Cdc42 from WASP, was used to examine the amide exchange from the Cdc42-bound state of GBD-C. The GTPase increases exchange rates of the most protected amides by 50-500-fold, with destabilization reducing the differences in the protection of segments in the free state. The results confirm that Cdc42 facilitates the physical separation of the GBD from the VCA in a tethered molecule, indicating this process likely plays an important role in activation of full-length WASP by the GTPase. However, destabilization of GBD-C is not complete in the Cdc42 complex. The data indicate that partitioning of free energy between binding and activation may limit the extent to which GTPases can cause conformational change in effectors. This notion is consistent with the requirement of multiple input signals in order to achieve maximal activation in many effector molecules.

Uridylylation of the PII protein from Herbaspirillum seropedicae

The PII protein is apparently involved in the control of NifA activity in Herbaspirillum seropedicae. To evaluate the probable role of PII in signal transduction, uridylylation assays were conducted with purified H. seropedicae PII and Escherichia coli GlnD, or a cell-free extract of H. seropedicae as sources of uridylylating activity. The results showed that alpha-ketoglutarate and ATP stimulate uridylylation whereas glutamine inhibits uridylylation. Deuridylylation of PII-UMP was dependent on glutamine and inhibited by ATP and alpha-ketoglutarate. PII uridylylation and (or) deuridylylation in response to these effectors suggests that PII is a nitrogen level signal transducer in H. seropedicae.

C/EBPbeta phosphorylation by RSK creates a functional XEXD caspase inhibitory box critical for cell survival

Upon activation by liver injury, hepatic stellate cells produce excessive fibrous tissue leading to cirrhosis. The hepatotoxin CCl(4) induced activation of RSK, phosphorylation of C/EBPbeta on Thr(217), and proliferation of stellate cells in normal mice, but caused apoptosis of these cells in C/EBPbeta-/- or C/EBPbeta-Ala(217) (a dominant-negative nonphosphorylatable mutant) transgenic mice. Both C/EBPbeta-PThr(217) and the phosphorylation mimic C/EBPbeta-Glu(217), but not C/EBPbeta-Ala(217), were associated with procaspases 1 and 8 in vivo and in vitro and inhibited their activation. Our data suggest that C/EBPbeta phosphorylation on Thr(217) creates a functional XEXD caspase substrate/inhibitor box (K-Phospho-T(217)VD) that is mimicked by C/EBPbeta-Glu(217) (KE(217)VD). C/EBPbeta-/- and C/EBPbeta-Ala(217) stellate cells were rescued from apoptosis by the cell permeant KE(217)VD tetrapeptide or C/EBPbeta-Glu(217).

Binding of transcriptional activators to sigma 54 in the presence of the transition state analog ADP-aluminum fluoride: insights into activator mechanochemical action

Conformational changes in sigma 54 (sigma(54)) and sigma(54)-holoenzyme depend on nucleotide hydrolysis by an activator. We now show that sigma(54) and its holoenzyme bind to the central ATP-hydrolyzing domains of the transcriptional activators PspF and NifA in the presence of ADP-aluminum fluoride, an analog of ATP in the transition state for hydrolysis. Direct binding of sigma(54) Region I to activator in the presence of ADP-aluminum fluoride was shown and inferred from in vivo suppression genetics. Energy transduction appears to occur through activator contacts to sigma(54) Region I. ADP-aluminum fluoride-dependent interactions and consideration of other AAA+ proteins provide insight into activator mechanochemical action.

The CRP-cAMP complex and downregulation of the glnAp2 promoter provides a novel regulatory linkage between carbon metabolism and nitrogen assimilation in Escherichia coli

In Escherichia coli, glnA (encoding glutamine synthetase) is transcribed from two promoters (glnAp1 and glnAp2). The glnAp1 is a sigma(70)-dependent promoter that is activated by the cAMP receptor protein (CRP). Under nitrogen-deficient growth conditions, glnAp1 is repressed by NtrC-phosphate. The downstream glnAp2 promoter is sigma(54)-dependent and is activated by NtrC-phosphate. Here, we show that glnAp2 expression is affected by different carbon sources and that the CRP-cAMP complex inhibits the glnAp2 promoter activity. Primer extension and KMnO4 footprinting analysis indicate that the inhibitory effect is at the transcriptional level in vivo. When glnAp2 is activated by NifA, a similar inhibitory effect by CRP-cAMP is observed. Site-directed mutagenesis and deletion analysis indicate that the characterized and putative CRP-binding sites located in the upstream region of the glnAp2 promoter are not essential for the inhibitory effect. CRP-cAMP inhibits sigma(54)-dependent glnAp2 strongly, by 21-fold. By activating glnAp1 and downregulating glnAp2, the overall effect of CRP-cAMP on glnA expression is an approximately fourfold reduction, which correlates with the reduction of gamma-glutamyl transferase activities in the cells. We propose therefore that a physiological role of CRP-cAMP activation of glnAp1 is to partially compensate for CRP-cAMP downregulation of glnAp2, allowing a low but non-negligible level of expression of the important genes transcribed from it. A novel regulatory linkage between carbon and nitrogen regulons is proposed.