Assay Buffer Research Articles

“The Whole is Greater than the Sum of Its Parts-” Hit Selection and the Power of Orthogonality

Biophysical methods are essential tools in current front line drug discovery processes. They can be used for optimization of protein constructs and verification of proper and consistent protein folding, identification of optimal assay buffer, screening of fragments and the confirmation of binding to the right or allosteric binding site(s) of the target molecule- each approach providing a wealth of information. With a growing industry need to reduce project attrition (and therefore cost) by providing more physiological mechanistic data to aid in the identification of compounds that translate in vitro activity into in vivo efficacy. Application of panels of biophysical techniques allow cross correlation of data and better control of experimental parameters - increasing reliability and confidence in results whilst eliminating artifacts. In this work we show how SPR, DSC and ITC can be used in the selection and verification of binders in a Fragment Based Drug Discovery campaign by providing quantitative binding information to advance true hits for chemistry and later stage biology in hit to lead development.

Hypoxia-inducible Factor-1α (HIF-1α) Protein Diminishes Sodium Glucose Transport 1 (SGLT1) and SGLT2 Protein Expression in Renal Epithelial Tubular Cells (LLC-PK1) under Hypoxia

In this work, we demonstrated the regulation of glucose transporters by hypoxia inducible factor-1α (HIF-1α) activation in renal epithelial cells. LLC-PK1 monolayers were incubated for 1, 3, 6, or 12 h with 0% or 5% O2 or 300 μm cobalt (CoCl2). We evaluated the effects of hypoxia on the mRNA and protein expression of HIF-1α and of the glucose transporters SGLT1, SGLT2, and GLUT1. The data showed an increase in HIF-1α mRNA and protein expression under the three evaluated conditions (p < 0.05 versus t = 0). An increase in GLUT1 mRNA (12 h) and protein expression (at 3, 6, and 12 h) was observed (p < 0.05 versus t = 0). SGLT1 and SGLT2 mRNA and protein expression decreased under the three evaluated conditions (p < 0.05 versus t = 0). In conclusion, our results suggest a clear decrease in the expression of the glucose transporters SGLT1 and SGLT2 under hypoxic conditions which implies a possible correlation with increased expression of HIF-1α.

CAMP-dependent Protein Kinase and c-Jun N-terminal Kinase Mediate Stathmin Phosphorylation for the Maintenance of Interphase Microtubules during Osmotic Stress

Dynamic microtubule changes after a cell stress challenge are required for cell survival and adaptation. Stathmin (STMN), a cytoplasmic microtubule-destabilizing phosphoprotein, regulates interphase microtubules during cell stress, but the signaling mechanisms involved are poorly defined. In this study ectopic expression of single alanine-substituted phospho-resistant mutants demonstrated that STMN Ser-38 and Ser-63 phosphorylation were specifically required to maintain interphase microtubules during hyperosmotic stress. STMN was phosphorylated on Ser-38 and Ser-63 in response to hyperosmolarity, heat shock, and arsenite treatment but rapidly dephosphorylated after oxidative stress treatment. Two-dimensional PAGE and Phos-tag gel analysis of stress-stimulated STMN phospho-isoforms revealed rapid STMN Ser-38 phosphorylation followed by subsequent Ser-25 and Ser-63 phosphorylation. Previously, we delineated stress-stimulated JNK targeting of STMN. Here, we identified cAMP-dependent protein kinase (PKA) signaling as responsible for stress-induced STMN Ser-63 phosphorylation. Increased cAMP levels induced by cholera toxin triggered potent STMN Ser-63 phosphorylation. Osmotic stress stimulated an increase in PKA activity and elevated STMN Ser-63 and CREB (cAMP-response element-binding protein) Ser-133 phosphorylation that was substantially attenuated by pretreatment with H-89, a PKA inhibitor. Interestingly, PKA activity and subsequent phosphorylation of STMN were augmented in the absence of JNK activation, indicating JNK and PKA pathway cross-talk during stress regulation of STMN. Taken together our study indicates that JNK- and PKA-mediated STMN Ser-38 and Ser-63 phosphorylation are required to preserve interphase microtubules in response to hyperosmotic stress.

Apolipoprotein A-IV Reduces Hepatic Gluconeogenesis through Nuclear Receptor NR1D1

We showed recently that apoA-IV improves glucose homeostasis by enhancing pancreatic insulin secretion in the presence of elevated levels of glucose. Therefore, examined whether apolipoprotein A-IV (apoA-IV) also regulates glucose metabolism through the suppression of hepatic gluconeogenesis. The ability of apoA-IV to lower gluconeogenic gene expression and glucose production was measured in apoA-IV(-/-) and wild-type mice and primary mouse hepatocytes. The transcriptional regulation of Glc-6-Pase and phosphoenolpyruvate carboxykinase (PEPCK) by apoA-IV was determined by luciferase activity assay. Using bacterial two-hybrid library screening, NR1D1 was identified as a putative apoA-IV-binding protein. The colocalization and interaction between apoA-IV and NR1D1 were confirmed by immunofluorescence, in situ proximity ligation assay, and coimmunoprecipitation. Enhanced recruitment of NR1D1 and activity by apoA-IV to Glc-6-Pase promoter was verified with ChIP and a luciferase assay. Down-regulation of apoA-IV on gluconeogenic genes is mediated through NR1D1, as illustrated in cells with NR1D1 knockdown by siRNA. We found that apoA-IV suppresses the expression of PEPCK and Glc-6-Pase in hepatocytes; decreases hepatic glucose production; binds and activates nuclear receptor NR1D1 and stimulates NR1D1 expression; in cells lacking NR1D1, fails to inhibit PEPCK and Glc-6-Pase gene expression; and stimulates higher hepatic glucose production and higher gluconeogenic gene expression in apoA-IV(-/-) mice. We conclude that apoA-IV inhibits hepatic gluconeogenesis by decreasing Glc-6-Pase and PEPCK gene expression through NR1D1. This novel regulatory pathway connects an influx of energy as fat from the gut (and subsequent apoA-IV secretion) with inhibition of hepatic glucose production.

High Activities of BACE1 in Brains with Mild Cognitive Impairment

We recently discovered elevated β-secretase 1 (BACE1) activity in brains with sporadic Alzheimer disease (AD). Moreover, we also found high levels of BACE1 enzymatic activity in the cerebrospinal fluid from patients with both mild cognitive impairment (MCI) and AD. These results suggest that elevation of BACE1 enzymatic activity may occur early or may contribute to AD. We therefore examined whether BACE1 enzymatic activity was changed in MCI brains. BACE1 activity and tumor necrosis factor (TNF)-α levels were measured by enzymatic assay and ELISA in the temporal cortex from 18 patients with clinically well-characterized AD, 18 patients with MCI, and 18 healthy controls. We found a significant increase in BACE1 activity and protein level in brains of MCI and AD patients. Moreover, increased BACE1 activity correlated with plaque numbers and cognition status. We also found an increase in TNF-α in MCI brains. Invitro study revealed that TNF-α rather than other cytokines can up-regulate BACE1 protein expression. These findings suggest that BACE1 increase occurs early in MCI and is possibly induced by TNF-α and that BACE1 enzymatic activity may be important for conversion of MCI to AD.

The inhibitory effects of silver diamine fluorides on cysteine cathepsins

AimThe expression of cysteine cathepsins in human carious dentine suggests that this enzyme contributes to the collagen degradation in caries progress. This study investigated whether silver diamine fluoride (SDF) inhibited the activity of cysteine cathepsins. MethodsThree commercial SDF solutions with concentrations at 38%, 30% and 12% were studied. Two fluoride solutions with the same fluoride ion (F-) concentrations as the 38% and 12% SDF solutions, and 2 silver solutions with the same silver ion (Ag+) concentrations as the 38% and 12% SDF solutions were prepared. Five samples of each experimental solution were used to study their inhibitory effect on two cathepsins (B and K) using cathepsin assay kits. Positive control contained assay buffer and cathepsins dilution was used to calculate the percentage inhibition (difference between the mean readings of the test solution and control solution divided by that of the control group). ResultsThe percentage inhibition of 38%, 30% and 12% SDF on cathepsin B were 92.0%, 91.5% and 90.3%, respectively (p<0.001); on cathepsin K were 80.6%, 78.5% and 77.9%, respectively (p<0.001). Ag+ exhibited the inhibitory effect against both cathepsin B and K with or without the presence of F- (p<0.01). The solutions containing Ag+ have significantly higher inhibitory effect than the solutions containing F- only (p<0.01). ConclusionAccording to this study, SDF solution at all 3 tested concentrations significantly inhibited the activity of cathepsin B and K.

Development of Functionally Selective, Small Molecule Agonists at Kappa Opioid Receptors

The kappa opioid receptor (KOR) is widely expressed in the CNS and can serve as a means to modulate pain perception, stress responses, and affective reward states. Therefore, the KOR has become a prominent drug discovery target toward treating pain, depression, and drug addiction. Agonists at KOR can promote G protein coupling and βarrestin2 recruitment as well as multiple downstream signaling pathways, including ERK1/2 MAPK activation. It has been suggested that the physiological effects of KOR activation result from different signaling cascades, with analgesia being G protein-mediated and dysphoria being mediated through βarrestin2 recruitment. Dysphoria associated with KOR activation limits the therapeutic potential in the use of KOR agonists as analgesics; therefore, it may be beneficial to develop KOR agonists that are biased toward G protein coupling and away from βarrestin2 recruitment. Here, we describe two classes of biased KOR agonists that potently activate G protein coupling but weakly recruit βarrestin2. These potent and functionally selective small molecule compounds may prove to be useful tools for refining the therapeutic potential of KOR-directed signaling in vivo.

Lithium Down-regulates Histone Deacetylase 1 (HDAC1) and Induces Degradation of Mutant Huntingtin

Lithium is an effective mood stabilizer that has been clinically used to treat bipolar disorder for several decades. Recent studies have suggested that lithium possesses robust neuroprotective and anti-tumor properties. Thus far, a large number of lithium targets have been discovered. Here, we report for the first time that HDAC1 is a target of lithium. Lithium significantly down-regulated HDAC1 at the translational level by targeting HDAC1 mRNA. We also showed that depletion of HDAC1 is essential for the neuroprotective effects of lithium and for the lithium-mediated degradation of mutant huntingtin through the autophagic pathway. Our studies explain the multiple functions of lithium and reveal a novel mechanism for the function of lithium in neurodegeneration.

Plasma Circulating Proteasomes As Biomarkers Along Natural History Of Asymptomatic Monoclonal Gammopathies

BackgroundMonoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM) are asymptomatic plasma cell dyscrasias with a heterogeneous probability to progress to symptomatic multiple myeloma (MM). Reliable markers for progression to MM are vital to advance the understanding of myeloma precursor disease and for the development of intervention trials designed to delay/prevent MM. The Mayo Clinic and Spanish PETHEMA have proposed models to stratify patient risk based on clinical parameters. At the current time, no molecular biomarkers have been established to determine risk of transformation. Based on the fact that MM tumor cells are highly sensitive to proteasome inhibition and that circulating proteasomes (cProt) have been detected in the blood of MM patients, we conducted a prospective clinical study designed to characterize patterns of cProt in peripheral blood from MGUS, SMM and MM patients. Patients and MethodsNinety two patients diagnosed with asymptomatic monoclonal gammopathies (39 MGUS and 53 SMM; median age 63 years; 46M/47F) were studied. This group was compared to normal sera from healthy donors (n=6) and untreated patients with recent diagnosed MM (n=38). Initial baseline demographics, clinical and laboratory data were collected. MGUS patients were classified according to Mayo Clinic risk score (M-protein, monoclonal isotype and serum FLC), while SMM could be stratified according to PETHEMA (malignant bone marrow plasma cell (BMPC) percentage and immunoparesis) and Mayo system (BMPC infiltration, serum M-protein and serum FLC). Plasma and bone marrow supernatant samples were collected at diagnosis and frozen to -80ºC. In 58 MGUS and SMM cases, sequential plasma samples at 6 months and 1 year were also analyzed. Chymotrypsin-like, caspase-like, and trypsin-like activities from cProt were assayed by continuously monitoring the production of 7-amino-4-methylcoumarin (AMC) from fluorogenic peptides by plasma. Briefly, samples were activated with SDS (for chymotrypsin-like and caspase-like) or 10% Tween-20 (for trypsin-like). The reaction wells contained 30 μL assay buffer (25 mmol/L HEPES), 10 μL activated sample, and 10 μL of the prospective fluorogenic peptide-AMC substrate. To measure the fluorescence release of free AMC with time, the SpectraMax M5 (Molecular Devices) instrument was used with a read interval of 1 min during 30 min at 37ºC. All samples were performed by triplicate. Enzymatic activities were quantified (pmol AMC/s/mL plasma) by generating a standard curve of AMC. ResultsMGUS patients had zero (38.5%), one (41%) or two risk factors (20.5%) according to the Mayo Clinic model. In contrast, 49% of the patients with SMM were classified as high-risk according to the PETHEMA model, versus 69.8% with 2 or 3 risk factors in the Mayo Clinic model. Chymotrypsin activity levels in plasma were statistically correlated with serum M-protein concentration and total IgG concentration (p<0.001). Chymotrypsin-like activity was differentially expressed in plasma across the different groups of patients (p=0.009; Figure 1). Particularly, SMM and MM showed higher levels than healthy controls and MGUS patients. In SMM, patients with highest-risk of transformation showed a higher levels of this chymotrypsin-like activity than the other groups (p=0.02). When only IgG SMM and MGUS patients were considered, a correlation with immunoparesis (reduction of IgM and IgA), BMPC infiltration, relative lower hemoglobin levels and higher FLC ratio (p<0.05) was observed. Caspase-like activity was also associated with diagnosis, showing higher levels in symptomatic and SMM patients than healthy donors and MGUS (p=0.016) (Figure 2) and correlated with IgG and serum M-protein (p=0.01 and p=0.006). In contrast, trypsin-like levels were negatively correlated along the spectrum of tumoral mass in the four groups (p=0.004) (Figure 3). Bone marrow supernatant chymotrypsin activity was higher in symptomatic MM than MGUS patients (p=0.004), with a trend for caspase. [Display omitted] [Display omitted] [Display omitted] ConclusionChymotrypsin-and caspase-like activity of circulating proteasome in asymptomatic gammopathies is related to tumoral mass and immunoparesis degree. MGUS patients are close to healthy individuals, with SMM not so different than symptomatic patients. Prognostic significance of these findings after longer follow-up is warranted. Disclosures:No relevant conflicts of interest to declare.

Enzymatic Activities Of Circulating Plasma Proteasomes (cProt) In Newly Diagnosed Multiple Myeloma (NDMM) Patients Undergoing Treatment With Carfilzomib, Lenalidomide and Dexamethasone (CRd)

BackgroundThe proteasome inhibitor carfilzomib is highly effective in the treatment of multiple myeloma (MM). It selectively and irreversibly binds the chymotrypsin-like (CHYM) active site in the β5 subunit of the proteasome. One prior retrospective study based on 50 NDMM patients found maintained elevated total cProt levels post therapy to be associated with poorer response to therapy and shorter overall survival (PMID: 17095627). We conducted a study based on NDMM patients treated with carfilzomib, lenalidomide and dexamethasone (CRd). The aim of this investigation was to assess the role of specific enzymatic activities of plasma cProt in relation to treatment responses. MethodsWe assessed 37 newly diagnosed MM patients from our ongoing clinical trial using CRd therapy (NCT01402284). Baseline demographic, clinical and laboratory parameters were collected. Plasma samples were collected at time intervals as specified in the protocol [C1D1 (baseline), C1D2 (post single dose carfilzomib), C2D1, C4D1 and C8D1] and frozen to -80ºC. Patient responses were assessed per current IMWG guidelines. CHYM, caspase-like (CASP), and trypsin-like (TRYP) activities from cProt were assayed by continuously monitoring the production of 7-amino-4-methylcoumarin (AMC) from fluorogenic peptides in plasma. Briefly, plasma samples were activated with SDS (for chymotrypsin-like and caspase-like) or 10% Tween-20 (for trypsin-like). The reaction wells contained 30 μL assay buffer (25 mmol/L HEPES), 10 μL activated sample, and 10 μL of the prospective fluorogenic peptide-AMC substrate. To measure the fluorescence release of free AMC with time, the SpectraMax M5 (Molecular Devices) instrument was used with a read interval of 1 min during 30 min at 37ºC. Samples were analyzed per triplicate. Enzymatic activities were quantified (pmol AMC/s/mL plasma) by generating a standard curve of AMC. A two tailed Wilcoxon signed rank test was used for comparisons across matched cProt values. The Mann Whitney Test was used to compare differences between two independent groups of cProt values. Spearman's rank correlation was used for correlation between cProt levels and clinical parameters. All p-values are two-tailed. ResultsPatients had a median age of 61 years (range 40-86; 57% males). Median M-spike was 2.7 (0.8-7.1) g/dL, isotypes included IgG (n=26), IgA (n=6), kappa (n=4) and lambda (n=1); International Staging System (ISS) Stage I (n=19) and II (n=18). Median C1D1 levels of chymotrypsin-like, caspase-like and trypsin-like activity for all patients were 0.84 (0.12-3.89), 0.85 (0.31-2.28) and 2.95 (1.4-7.39) pmol AMC/s/ml plasma, respectively. CHYM and CASP C1D1 levels correlated with the levels of baseline IgG (r=0.42, CHYM; r=0.38 CASP) and the levels of baseline β2-microglobulin (r=0.37, CHYM; r=0.45, CASP). Additionally, CHYM correlated with levels of free kappa (r=0.33) and levels of serum M-protein (r=0.34); and CASP correlated with the percentage of plasma cell infiltration in core bone marrow biopsy (r=0.36). Baseline TRYP levels did not correlate with clinical parameters. Median CHYM (1.3 versus 0.7 pmol AMC/s/ml plasma) and CASP (1.0 versus 0.7 pmol AMC/s/ml plasma) levels, but not TRYP levels, were were non-significantly elevated in Stage II ISS compared to Stage I patients. CHYM levels after an initial single dose of carfilzomib were reduced by a median of 68.2% (p<0.05), whereas CASP and TRYP levels were increased by 5.3% (p>0.05) and 0.4% (p>0.05), respectively. CASP and TRYP levels measured at C2D1, C4D1 and C8D1 remained stable throughout treatment cycles. When compared to baseline, median CHYM levels decreased significantly at C1D2 (after one dose of carfilzomib), then increased at C2D1 and steadily decreased again throughout treatment at the C4D1 and C8D1 time intervals. ConclusionsIn newly diagnosed MM patients, pre-treatment CHYM and CASP plasma activity levels were non-significantly higher among patients with higher ISS stage. Peripheral blood collected 24 hours after a single dose carfilzomib showed reduced CHYM levels by >60% in most patients. Fluctuations in CHYM, CASP and TRYP levels were noted throughout CRd treatment; no consistent patterns were observed in relation to response to therapy. Disclosures:No relevant conflicts of interest to declare.

Monoclonal Antibody Production and the Development of an Indirect Competitive Enzyme-Linked Immunosorbent Assay for Screening Spiramycin in Milk

To monitor spiramycin (SP) residue in milk, a monoclonal antibody (mAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed. This study described the preparation of three immunogens and the production of a high-affinity mAb. After optimization, the 50% inhibition concentration (IC50) for the developed icELISA was estimated as 0.97 ng/mL in the assay buffer, and the limit of detection and limit of quantitation were 2.51 and 4.40 μg/L in the milk matrix. The newly developed assay demonstrated negligible cross-reactivity with 15 other macrolide antibiotics, but not with kitasamycin (23.4%). The mean recoveries ranged from 81 to 103% for the spiked samples (5, 10, and 50 μg/L), and the coefficient of variation ranged from 5.4 to 9.6%. The icELISA was validated by LC-MS/MS method, and all results demonstrated that it was a suitable screening method for detecting SP residue in milk without requiring a cleanup process.

Crystal Structure and Pharmacological Characterization of a Novel N-Methyl-d-aspartate (NMDA) Receptor Antagonist at the GluN1 Glycine Binding Site

NMDA receptors are ligand-gated ion channels that mediate excitatory neurotransmission in the brain. They are tetrameric complexes composed of glycine-binding GluN1 and GluN3 subunits together with glutamate-binding GluN2 subunits. Subunit-selective antagonists that discriminate between the glycine sites of GluN1 and GluN3 subunits would be valuable pharmacological tools for studies on the function and physiological roles of NMDA receptor subtypes. In a virtual screening for antagonists that exploit differences in the orthosteric binding site of GluN1 and GluN3 subunits, we identified a novel glycine site antagonist, 1-thioxo-1,2-dihydro-[1,2,4]triazolo[4,3-a]quinoxalin-4(5H)-one (TK40). Here, we show by Schild analysis that TK40 is a potent competitive antagonist with Kb values of 21-63 nM at the GluN1 glycine-binding site of the four recombinant GluN1/N2A-D receptors. In addition, TK40 displayed >100-fold selectivity for GluN1/N2 NMDA receptors over GluN3A- and GluN3B-containing NMDA receptors and no appreciable effects at AMPA receptors. Binding experiments on rat brain membranes and the purified GluN1 ligand-binding domain using glycine site GluN1 radioligands further confirmed the competitive interaction and high potency. To delineate the binding mechanism, we have solved the crystal structure of the GluN1 ligand-binding domain in complex with TK40 and show that TK40 binds to the orthosteric binding site of the GluN1 subunit with a binding mode that was also predicted by virtual screening. Furthermore, the structure reveals that the imino acetamido group of TK40 acts as an α-amino acid bioisostere, which could be of importance in bioisosteric replacement strategies for future ligand design.

Polyamines Are Critical for the Induction of the Glutamate Decarboxylase-dependent Acid Resistance System in Escherichia coli

As part of our studies on the biological functions of polyamines, we have used a mutant of Escherichia coli that lacks all the genes for polyamine biosynthesis for a global transcriptional analysis on the effect of added polyamines. The most striking early response to the polyamine addition is the increased expression of the genes for the glutamate-dependent acid resistance system (GDAR) that is important for the survival of the bacteria when passing through the acid environment of the stomach. Not only were the two genes for glutamate decarboxylases (gadA and gadB) and the gene for glutamate-γ-aminobutyrate antiporter (gadC) induced by the polyamine addition, but the various genes involved in the regulation of this system were also induced. We confirmed the importance of polyamines for the induction of the GDAR system by direct measurement of glutamate decarboxylase activity and acid survival. The effect of deletions of the regulatory genes on the GDAR system and the effects of overproduction of two of these genes were also studied. Strikingly, overproduction of the alternative σ factor rpoS and of the regulatory gene gadE resulted in very high levels of glutamate decarboxylase and almost complete protection against acid stress even in the absence of any polyamines. Thus, these data show that a major function of polyamines in E. coli is protection against acid stress by increasing the synthesis of glutamate decarboxylase, presumably by increasing the levels of the rpoS and gadE regulators.

Redox Control of the Senescence Regulator Interleukin-1α and the Secretory Phenotype

Senescent cells accumulate in aged tissue and are causally linked to age-associated tissue degeneration. These non-dividing, metabolically active cells are highly secretory and alter tissue homeostasis, creating an environment conducive to metastatic disease progression. IL-1α is a key senescence-associated (SA) proinflammatory cytokine that acts as a critical upstream regulator of the SA secretory phenotype (SASP). We established that SA shifts in steady-state H2O2 and intracellular Ca(2+) levels caused an increase in IL-1α expression and processing. The increase in intracellular Ca(2+) promoted calpain activation and increased the proteolytic cleavage of IL-1α. Antioxidants and low oxygen tension prevented SA IL-1α expression and restricted expression of SASP components IL-6 and IL-8. Ca(2+) chelation or calpain inhibition prevented SA processing of IL-1α and its ability to induce downstream cytokine expression. Conditioned medium from senescent cells treated with antioxidants or Ca(2+) chelators or cultured in low oxygen markedly reduced the invasive capacity of proximal metastatic cancer cells. In this paracrine fashion, senescent cells promoted invasion by inducing an epithelial-mesenchymal transition, actin reorganization, and cellular polarization of neighboring cancer cells. Collectively, these findings demonstrate how SA alterations in the redox state and Ca(2+) homeostasis modulate the inflammatory phenotype through the regulation of the SASP initiator IL-1α, creating a microenvironment permissive to tumor invasion.

Activation of the Leukotriene B4 Receptor 2-Reactive Oxygen Species (BLT2-ROS) Cascade following Detachment Confers Anoikis Resistance in Prostate Cancer Cells

The majority of prostate cancer-related deaths are associated with advanced and metastatic malignancies. Although anoikis resistance has been recognized as one of the hallmarks of metastatic prostate malignancies, the molecular events that cause anoikis resistance are poorly understood. In this study, we found that the detachment of PC-3 prostate cancer cells caused a time-dependent increase in the expression level of the leukotriene B4 receptor-2 (BLT2) and that BLT2 played a critical role in establishing anoikis resistance in these cells. Blocking BLT2 with the pharmacological inhibitor LY255283 or with RNAi knockdown clearly abolished anoikis resistance and resulted in severe apoptotic death. Additionally, we demonstrated that the activation of NADPH oxidase (NOX) and subsequent generation of reactive oxygen species (ROS) were downstream of BLT2 signaling and led to the activation of NF-κB, thus establishing anoikis resistance during cell detachment. Furthermore, we observed that the ectopic expression of BLT2 in normal prostate PWR-1E cells rendered the cells resistant to anoikis and apparently diminished apoptotic cell death following detachment. Taken together, our results suggest that BLT2-NOX-ROS-NF-κB cascade induction during detachment confers a novel mechanism of anoikis resistance in prostate cancer cells and potentially contributes to prostate cancer progression.

Actin Monomers Activate Inverted Formin 2 by Competing with Its Autoinhibitory Interaction

INF2 is an unusual formin protein in that it accelerates both actin polymerization and depolymerization, the latter through an actin filament-severing activity. Similar to other formins, INF2 possesses a dimeric formin homology 2 (FH2) domain that binds filament barbed ends and is critical for polymerization and depolymerization activities. In addition, INF2 binds actin monomers through its diaphanous autoregulatory domain (DAD) that resembles a Wiskott-Aldrich syndrome protein homology 2 (WH2) sequence C-terminal to the FH2 that participates in both polymerization and depolymerization. INF2-DAD is also predicted to participate in an autoinhibitory interaction with the N-terminal diaphanous inhibitory domain (DID). In this work, we show that actin monomer binding to the DAD of INF2 competes with the DID/DAD interaction, thereby activating actin polymerization. INF2 is autoinhibited in cells because mutation of a key DID residue results in constitutive INF2 activity. In contrast, purified full-length INF2 is constitutively active in biochemical actin polymerization assays containing only INF2 and actin monomers. Addition of proteins that compete with INF2-DAD for actin binding (profilin or the WH2 from Wiskott-Aldrich syndrome protein) decrease full-length INF2 activity while not significantly decreasing activity of an INF2 construct lacking the DID sequence. Profilin-mediated INF2 inhibition is relieved by an anti-N-terminal antibody for INF2 that blocks the DID/DAD interaction. These results suggest that free actin monomers can serve as INF2 activators by competing with the DID/DAD interaction. We also find that, in contrast to past results, the DID-containing N terminus of INF2 does not directly bind the Rho GTPase Cdc42.

A sensitive chemiluminescent enzyme immunoassay for carbofuran residue in vegetable, fruit and environmental samples

Using the direct competitive chemiluminescent enzyme immunoassay (CLEIA), a rapid, highly selective and sensitive method for carbofuran determination was developed. Several physicochemical parameters such as chemiluminescent sensitiser, assay buffer, blocking substance and working concentration were optimised. Under the optimum conditions, the CLEIA method for carbofuran determination was generated successfully. The detection sensitivity of the IC50 value was 4.2 ng/mL at a practical working concentration ranging from 0.4 to 50 ng/mL, and the limit of detection (LOD) for carbofuran was 0.5 ng/mL. Recoveries of carbofuran spiked into vegetable, fruit and environmental samples were determined by CLEIA after sample matrix effect testing. Finally, the confirmation test between CLEIA and LC-MS/MS was finished. The results showed that CLEIA method had higher sensitivity than enzyme-linked immunosorbent assay method, and the LOD of a variety of samples reached the carbofuran's maximum residue limit value laid down by Codex Alimentarius Commission.

Abstract 62: Novel role of Aminopeptidase A enzyme in Ang-(1-7) metabolism Post Myocardial Infarction

Aminopeptidase A (APA) is a metalloprotease that is activated in cardiovascular diseases. Ang-(1-7) has been shown to have beneficial effects in myocardial injury. The aims of this study are to (1) Test the role of APA in cardiac pathology using the myocardial infarction (MI) model, (2) Investigate the role of APA in Ang-(1-7) metabolism (3) Explore the effect of APA inhibition on Ang-(1-7) homeostasis. APA activity was measured using mass spectrometry (MS) based in vitro and in situ enzyme assays. For the in vitro assay, heart homogenates were incubated with 50 μM Ang II in assay buffer and for absolute quantitation stable-isotope labeled internal standards were added. In the in situ MS imaging, frozen myocardial sections were incubated with 100 μM Ang II for 10 min and the resultant peptides were assessed on the tissue sections. For kinetic studies and Km determination, recombinant APA was incubated with Ang II and Ang-(1-7) in concentrations ranging from 1-100 μM. Results from the in vitro MS enzyme assays showed that myocardial APA activity was significantly increased after 24 hrs MI compared to sham (Ang III=0.82±0.02 vs. 0.32± 0.02 ρmol/min/μg in MI vs sham, respectively, p&lt;0.01). The in situ MS imaging results confirmed that Ang III intensity was higher in MI heart sections compared to sham (96325±214 for MI and 1041±75 AU for Sham, p&lt;0.05). Both MS enzyme assays identified a new peptide Ang-(2-7), m/z 784, which accumulated in the MI compared to Sham (136.96± 6.5 vs 78.94±3 AU in MI and Sham, respectively, p&lt;0.05). Inhibition of APA with 4-Amino-phosphono-butyric acid significantly decreased formation of Ang-(2-7) from Ang-(1-7) and Ang III from Ang II by 98± 0.7% and 82±2.6% (p&lt;0.05), respectively, indicating that APA is the responsible enzyme for the myocardial formation of both peptides. Interestingly, APA exhibited a higher substrate affinity for Ang-(1-7) compared to Ang II (Km for Ang II=14.32±1.6 vs Km for Ang-(1-7) =6.34± 1.12 μM, p&lt;0.05). In conclusion, we have shown for the first time that APA is responsible for Ang-(1-7) degradation to Ang-(2-7). An upregulation of this pathway in myocardial injury may deprive the heart of cardioprotective Ang-(1-7). Thus, APA can be a potentially novel therapeutic target for management of myocardial remodeling after MI.

Kinetic Characterization of the ATPase and Actin-activated ATPase Activities of Acanthamoeba castellanii Myosin-2

Phosphorylation of Ser-639 in loop-2 of the catalytic motor domain of the heavy chain of Acanthamoeba castellanii myosin-2 and the phosphomimetic mutation S639D have been shown previously to down-regulate the actin-activated ATPase activity of both the full-length myosin and single-headed subfragment-1 (Liu, X., Lee, D. Y., Cai, S., Yu, S., Shu, S., Levine, R. L., and Korn, E. D. (2013) Proc. Natl. Acad. Sci. U.S.A. 110, E23-E32). In the present study we determined the kinetic constants for each step in the myosin and actomyosin ATPase cycles of recombinant wild-type S1 and S1-S639D. The kinetic parameter predominantly affected by the S639D mutation is the actin-activated release of inorganic phosphate from the acto myosin·ADP·Pi complex, which is the rate-limiting step in the steady-state actomyosin ATPase cycle. As consequence of this change, the duty ratio of this conventional myosin decreases. We speculate on the effect of Ser-639 phosphorylation on the processive behavior of myosin-2 filaments.

Myocilin Mediates Myelination in the Peripheral Nervous System through ErbB2/3 Signaling

The glaucoma-associated gene, myocilin, is expressed in ocular and non-ocular tissues including the peripheral nervous system, but its functions in these tissues remain poorly understood. We demonstrate that in sciatic nerve, myocilin is expressed in Schwann cells with high concentrations at the nodes of Ranvier. There, myocilin interacts with gliomedin, neurofascin, and NrCAM, which are essential for node formation and function. Treatment of isolated dorsal root ganglion cultures with myocilin stimulates clustering of the nodal proteins neurofascin and sodium channel Nav1.2. Sciatic nerves of myocilin null mice express reduced levels of several myelin-associated and basal membrane proteins compared with those of wild-type littermates. They also demonstrate reduced myelin sheath thickness and partial disorganization of the nodes. Myocilin signaling through ErbB2/3 receptors may contribute to these observed effects. Myocilin binds to ErbB2/ErbB3, activates these receptors, and affects the downstream PI3K-AKT signaling pathway. These data implicate a role for myocilin in the development and/or maintenance of myelination and nodes of Ranvier in sciatic nerve.