RING domains functioning as E3 ligases reveal distinct structural features: a molecular dynamics simulation study.

RING domain, a cysteine-rich motif that chelates two zinc ions, has been shown to regulate many biological processes such as mediating a crucial step in the ubiquitinylation pathway. In order to investigate the distinct structural features for the RING domains functioning as E3 ligases, several molecular dynamics simulations involving the c-Cbl, CNOT4 (with E3 ligase function), and p44 (no E3 ligase function) RING domains were conducted in this study. Our results reveal that the structural stability of the recognition site is a basic requirement for the RING domains functioning as E3 ligases. The structural stability of the recognition site is maintained by the hydrophobic core and hydrogen bonding network. Another important structural feature of the RING domains functioning as E3 ligases is the stable distances between the recognition site and the zinc ion binding sites S1 and S2. Moreover, the RING domains functioning as E3 ligases seem to exhibit lower beta stability due to the higher proportion of proline residues in their sequences. However, no significant difference of the other secondary (alpha and turn) and the tertiary structural stabilities can be observed among these three RING domains.

Synthetic biodegradable microparticles for articular cartilage tissue engineering.

Articular cartilage tissue engineering procedures require the transplantation of chondrocytes that have been expanded in vitro. The expansion is carried out for a considerable time and can lead to a modulation of cell phenotype. However, microcarrier cultures have been shown to allow cell expansion while maintaining the phenotype. Here, we have used the biodegradable polyester poly(lactide-co-glycolide) (PLGA) in the form of microspheres and irregular shaped microparticles with a diameter between 47 and 210 microm. Surface modification of particles was carried out by ammonia plasma treatment and subsequent adsorption of collagen. Alternatively, particles were modified by partial hydrolysis and subsequent immobilization of an amine-terminated dendrimer. Each surface modification step was characterized by X-ray photoelectron spectroscopy. The effectiveness of the surface modification procedures was demonstrated by in vitro cell culture experiments using sheep articular cartilage chondrocytes. A significant influence of both the particle shape and the surface chemistry on the proliferation rate was observed while the phenotype was maintained independent of the surface chemistry or particle shape. Chondrocytes cultured on PLGA microspheres were further assessed for cartilage tissue formation in collagen type I gels in nude mice. The tissue that were formed showed the appearance of a hyaline-like cartilage and the presence of the microspheres substantially reduced the degree of collagen gel contraction over 1-2 months.

Gelatin methacrylate/carboxybetaine methacrylate hydrogels with tunable crosslinking for controlled drug release.

In this work, methacrylated gelatin (GelMA) based hydrogels were fabricated with carboxybetaine methacrylate (CBMA) to manipulate the properties of the gelatin-based hydrogels, since CBMA is a much smaller compound compared to gelatin. With the incorporation of CBMA, these hydrogels demonstrated better mechanical properties, a slower degradation rate, and a controlled drug release rate compared with the GelMA alone group. GelMA/CBMA hydrogels also showed good cell viability. As in the in vivo test, vascular endothelial growth factor (VEGF)-loaded GelMA/CBMA hydrogels displayed certain degrees of angiogenesis. These results indicate that GelMA/CBMA hydrogels are biocompatible, and the properties of GelMA/CBMA hydrogels can be easily tuned with the ratio of CBMA. These characteristics make the GelMA/CBMA hydrogel a promising material for drug delivery and tissue engineering.

Gas6/Axl is the sensor of arginine-auxotrophic response in targeted chemotherapy with arginine-depleting agents.

Many human malignancies lack de novo biosynthesis of arginine (Arg) as the key enzyme argininosuccinate synthetase 1 (ASS1) is silenced. These tumors acquire ectopic Arg for survival, and depleting this source by Arg-depleting recombinant enzyme ADI-PEG20 results in cell death. Mechanisms underlying Arg auxotrophy in these tumors and how they respond to Arg-auxotrophic stress are poorly understood. Here, we report that an immediate-early event of Arg-auxotrophic response involves reactive oxygen species-mediated secretion of Gas6, which interacts with its receptor Axl and activates the downstream Ras/PI3K/Akt growth signal leading to accumulation of c-Myc by protein stabilization. Arg-auxotrophic challenge also transcriptionally upregulates c-Myc expression, which provides a feedback mechanism to enhance Axl expression. c-Myc is a positive regulator of ASS1, but elevated ASS1 provides a feedback mechanism to suppress c-Myc and Axl. Our results revealed multiple inter-regulatory pathways in Arg-auxotrophic response, consisting of Axl, c-Myc and ASS1, which regulate Arg homeostasis and ADI-PEG20 sensitivity. These pathways provide potential targets for improving the efficacy of treating Arg-auxotrophic tumors using Arg-deprivation strategies.

The effect of adsorbed fibrinogen, fibronectin, von Willebrand factor and vitronectin on the procoagulant state of adherent platelets.

Procoagulant (activated) platelets provide a site for assembly of the prothrombinase complex which can rapidly convert prothrombin into thrombin (a potent inducer of clot formation). Previously, we reported that adhesion of platelets to surfaces preadsorbed with blood plasma caused them to become procoagulant. In the present study we investigated the effect of adsorbed adhesion proteins (fibrinogen (Fg), fibronectin (Fn), von Willebrand factor (vWF) and vitronectin (Vn)) on the procoagulant activity of adherent platelets. Adsorbed Fn, vWF and Fg promoted platelet adhesion in the following order: Fn < vWF = Fg. However, these proteins promoted platelet activation (thrombin generation per adherent platelet) in the following order: Fg < Fn < vWF. Adsorption with a series of dilutions of normal plasma, serum, and plasmas deficient in or depleted of von Willebrand factor (de-vWF), fibronectin (de-Fn), vitronectin (de-Vn), or both vitronectin and fibronectin (de-VnFn) resulted in varied platelet adhesion, but little difference in platelet activation. However, preadsorption with dilute de-vWF plasma induced lower procoagulant activity than normal plasma. Preadsorption with normal plasma resulted in higher levels of platelet activation than preadsorption with Fg, suggesting that adsorption of plasma proteins other than Fg caused the high levels of activation observed for plasma preadsorbed surfaces.

Preparation of micron/submicron hybrid patterns via a two-stage UV-imprint technique and their dimensional effects on cell adhesion and alignment.

Cell adhesion, movement and proliferation on a biomaterial have been broadly explored and known to be induced by the morphology and structure of material surfaces. In order to explore the effects of hybrid structures (combination of micro- and nanofeatures on a pattern) on cell adhesion and alignment, a micro-featured mold was firstly prepared using partial UV-irradiation and the protruding top of the mold was then imprinted with nano-featured templates via successive UV irradiation. An oxygen inhibition effect was utilized in the course of UV curing and a two-step molding process, to form multiscale hybrid structures. The poly(dimethyl siloxane) (PDMS) replica of the hybrid mold was manufactured and employed to fabricate hybrid polymeric patterns for cell attachment. The underlying micro-feature was chosen to be a 25-µm-wide pattern and the nanostructures on the protrusions of the micropattern were different ruled nanogrooves, either parallel or perpendicular to the micro-featured pattern. In cell attachment measurement, 3T3 fibroblasts attached to poly(methyl methacrylate) (PMMA) samples seemed to be preferentially located on the recessed area of the hybrid patterns; however, 3T3 fibroblasts were aligned with nano-features, no matter if the nanogrooves were parallel or perpendicular to the micro-featured patterns. The nanogroove size was found to determine the effectiveness of cell alignment.

The role of fibronectin in platelet adhesion to plasma preadsorbed polystyrene.

Platelet adhesion to synthetic surfaces that come in contact with blood is mediated by the adsorption of adhesive plasma proteins, especially fibrinogen. However, the roles of other adhesive proteins, such as fibronectin, vitronectin, and von Willebrand factor in platelet adhesion are not yet clear. In this study, the role of fibronectin in platelet adhesion to surfaces was assessed using three approaches. First, platelet adhesion was measured on Immulon I preadsorbed with fibronectin-depleted plasma or fibronectin-depleted plasma replenished with increasing amount of fibronectin. Under these conditions, fibronectin adsorbed from plasma did not have any effect on platelet adhesion, while fibrinogen played a major role in mediating platelet adhesion. Since fibronectin might play a role in platelet adhesion to surfaces which adsorb little or no fibrinogen, we also used two other strategies to assess the potential role of fibronectin. One was to use platelets treated with a platelet activation inhibitor, prostaglandin E1, which prevents the activation of platelet fibrinogen receptor GP IIb/IIIa. The adhesion of prostaglandin E1-treated platelets to Immulon I preadsorbed with plasma was greatly decreased compared to that of untreated platelets, but was increased by the addition of supernormal concentrations of fibronectin to the plasma. This suggests that GP Ic/IIa, rather than GP IIb/IIIa, might be the platelet receptor which is responsible for platelet adhesion to surface-bound fibronectin. Finally, we studied the effect of fibronectin on platelet adhesion to surfaces preadsorbed with fibronectin-depleted afibrinogenemic plasma. We found that fibronectin re-addition to fibronectin-depleted afibrinogenemic plasma increased platelet adhesion. However, our most important finding was that fibronectin seems to play little or no role in mediating platelet adhesion to polystyrene surfaces preadsorbed with normal plasma.

Hemocompatibility of treated polystyrene substrates: contact activation, platelet adhesion, and procoagulant activity of adherent platelets.

Platelet adhesion to biomaterials is often used as an index of blood compatibility, but a more clinically relevant issue is whether the adherent platelets are able to promote clot formation (i.e., if they are in the procoagulant state). Platelets rapidly generate thrombin when they are in the procoagulant state and the VA/Xa complex is present. We found that adherent platelets are procoagulant by three different methods: binding of FITC-Annexin V, acceleration of thrombin generation in the presence of Xa, Va, and prothrombin; and clotting of recalcified plasma. In the clotting times studies, the effect of adherent platelets on TCPS was completely eliminated by the addition of Annexin V, which is known to bind tightly to procoagulant platelets. The degree of procoagulant activity of adherent platelets was determined by measuring thrombin generation rates in the presence of the clotting factors Va, Xa, and prothrombin and normalizing to the number of adherent platelets. Two key observations were made in these studies. First, the procoagulant activity of platelets adherent to untreated and to several types of treated polystyrenes, as well as to glass and PET, was much greater than the procoagulant activity of unstimulated bulk phase platelets. Little difference in the procoagulant activity of adherent platelets was observed among the materials tested, however. Second, the procoagulant activity of platelets prestimulated with ionophore and subsequently allowed to adhere to Plastek M was much greater than when adherent platelets were stimulated by the adhesion event only. Measured values for platelet adhesion, platelet activation, and contact activation of blood plasma are discussed in the context of their potential combined impact on blood clotting.

Co-adsorbed fibrinogen and von Willebrand factor augment platelet procoagulant activity and spreading.

Previously we observed that platelets adherent to surfaces preadsorbed with blood plasma exhibited 1.3 to 2.4 times greater procoagulant activity than platelets on surfaces adsorbed with fibrinogen (Fg) only. These observations suggested that the adhesion proteins adsorbed from plasma may activate platelets in a cooperative, or synergistic manner. In the present study, polystyrene surfaces adsorbed with both Fg and vWF induced up to three times greater procoagulant activity than surfaces adsorbed with Fg or vWF only. The amounts of Fg and vWF adsorbed from binary mixtures that resulted in increased procoagulant activity were found to be similar to the amounts that adsorbed to PS from 100% plasma. The effect of adsorbed adhesion proteins on platelet spreading was also investigated. The proportion of fully spread platelets increased, depending on the adhesion protein preadsorbed to the surface, in the following order: vWF < Fg < Fn < (vWF + Fg) < Vn < plasma.

Human plasma fibrinogen adsorption and platelet adhesion to polystyrene.

The purpose of this study was to further investigate the role of fibrinogen adsorbed from plasma in mediating platelet adhesion to polymeric biomaterials. Polystyrene was used as a model hydrophobic polymer; i.e., we expected that the role of fibrinogen in platelet adhesion to polystyrene would be representative of other hydrophobic polymers. Platelet adhesion was compared to both the amount and conformation of adsorbed fibrinogen. The strategy was to compare platelet adhesion to surfaces preadsorbed with normal, afibrinogenemic, and fibrinogen-replenished afibrinogenemic plasmas. Platelet adhesion was determined by the lactate dehydrogenase (LDH) method, which was found to be closely correlated with adhesion of 111In-labeled platelets. Fibrinogen adsorption from afibrinogenemic plasma to polystyrene (Immulon I(R)) was low and <10 ng/cm2. Platelet adhesion was absent on surfaces preadsorbed with afibrinogenemic plasma when the residual fibrinogen was low enough (<60 microg/mL). Platelet adhesion was restored on polystyrene preadsorbed with fibrinogen-replenished afibrinogenemic plasma. Addition of even small, subnormal concentrations of fibrinogen to afibrinogenemic plasma greatly increased platelet adhesion. In addition, surface-bound fibrinogen's ability to mediate platelet adhesion was different, depending on the plasma concentration from which fibrinogen was adsorbed. These differences correlated with changes in the binding of a monoclonal antibody that binds to the Aalpha chain RGDS (572-575), suggesting alteration in the conformation or orientation of the adsorbed fibrinogen. Platelet adhesion to polystyrene preadsorbed with blood plasma thus appears to be a strongly bivariate function of adsorbed fibrinogen, responsive to both low amounts and altered states of the adsorbed molecule.

Fyn kinase-tubulin interaction during meiosis of rat eggs.

Prior to fertilization, the spindle of vertebrate eggs must remain stable and well organized during the second meiotic meta-phase arrest (MII). In a previous study we have determined that the completion of meiosis is a Src family kinase (SFK)-dependent event. In the current study we have used the SFK inhibitors, SU6656 and PP2, and demonstrated that inhibition of SFKs caused the formation of a disorganized spindle. The observation that proper organization of an MII spindle is an SFK-dependent process, combined with our previous finding that Fyn kinase is localized at the microtubules (MTs), prompted us to examine the potential role of Fyn in MT signaling. Our results show an association between Fyn and tubulin, the ability of Fyn to phosphorylate tubulin in vitro and stimulation of meiosis completion by injection of a constitutively active form of Fyn (CAF). We suggested that SFKs mediate significant functions during the organization of the MII spindle. In view of CAF injection experiments, and of the pronounced concentration of Fyn kinase at the spindle, we propose that Fyn may play an important role in some aspects of the spindle functions, possibly those involving the MTs.

Platelet adhesion to radiofrequency glow-discharge-deposited fluorocarbon polymers preadsorbed with selectively depleted plasmas show the primary role of fibrinogen.

Fluorocarbon radio-frequency glow-discharge (RFGD) treatment has previously been shown to cause decreased platelet adhesion despite the presence of adsorbed fibrinogen on the surfaces. In this study platelet adhesion to fluorocarbon RFGD-treated surfaces preadsorbed with human plasma was further examined. A series of plasma deposited fluorocarbon thin films were made by varying the C3F6/CH4 ratio in the monomer feed. The surfaces were preadsorbed with plasma, serum, or plasma selectively depleted of fibronectin, vitronectin, or Von Willebrand factor, and platelet adhesion was measured. We also measured fibrinogen adsorption to the surfaces from plasma, monoclonal antibody binding to adsorbed fibrinogen and SDS elutability of the adsorbed fibrinogen. The antibodies used bind to the three putative platelet binding sites on fibrinogen, namely, M1 antibody binds to the dodecapeptide at the C-terminus of the gamma chain, gamma (402-411), R1 antibody binds to a sequence in the Aalpha chain (87-100) which includes RGDF at Aalpha (95-98) and R2 antibody binds a sequence in the Aalpha chain (566-580) which includes RGDS at Aalpha (572-575). Fibrinogen was found to play a decisive role in mediating platelet adhesion to the fluorocarbon surfaces contacting plasma. Few platelets adhered to the fluorocarbon surfaces preadsorbed with serum, while preadsorption with plasma selectively-depleted of either fibronectin, vitronectin, or von Willebrand factor did not decrease platelet adhesion significantly. Replenishment of exogenous fibrinogen to serum restored platelet adhesion, while replenishment of the other proteins had no effect. Platelet adhesion to the fluorocarbon surfaces was lower than to PET or the methane glow-discharge-treated PET. However, there was no apparent correlation between platelet adhesion and the amount of fibrinogen adsorption or monoclonal antibody binding to surface-bound fibrinogen.

Primary structure and characterization of an androgen-stimulated autoantigen purified from mouse seminal-vesicle secretion.

A protein extract of mouse seminal-vesicle secretion was used to immunize mature mice (Balb/c) of both sexes. Results of Western-blot analyses for these secretory proteins indicated that only one minor protein component could be recognized by the autoantisera prepared from either autoimmunization of male mice or isoimmunization of female mice. The autoantigen was purified from seminal-vesicle secretion. The purified autoantigen retained the ability to induce autoantibody formation. The autoantigen has glycoprotein characteristics: the majority of the carbohydrate is N-linked and the remainder is O-linked. Rabbit antibodies to the autoantigen were used to isolate the corresponding cDNA from a mouse seminal-vesicle cDNA library. The primary structure deduced from the cDNA sequence was confirmed by direct amino acid sequence determination. The results indicate that the core protein consists of 131 amino acid residues. Analysis of the primary structure indicates that the autoantigen has two potential acceptor sites for the N-linked carbohydrate at Asn-12 and Asn-122, three potential phosphorylation sites for casein kinase II at Thr-55, Ser-68 and Thr-76, and three potential phosphorylation sites for protein kinase C at Thr-28, Thr-40 and Thr-124. The core protein and the carbohydrate portion together have a molecular mass of 19 kDa. Results from Western- and Northern-blot analyses for various tissues indicate that the seminal vesicle is the sole organ producing this autoantigen. Expression of this autoantigen gene was stimulated by testosterone.

Template-imprinted nanostructured surfaces for protein recognition.

Synthetic materials capable of selectively recognizing proteins are important in separations, biosensors and the development of biomedical materials. The technique of molecular imprinting creates specific recognition sites in polymers by using template molecules. Molecular recognition is attributed to binding sites that complement molecules in size, shape and chemical functionality. But attempts to imprint proteins have met with only limited success. Here we report a method for imprinting surfaces with protein-recognition sites. We use radio-frequency glow-discharge plasma deposition to form polymeric thin films around proteins coated with disaccharide molecules. The disaccharides become covalently attached to the polymer film, creating polysaccharide-like cavities that exhibit highly selective recognition for a variety of template proteins, including albumin, immunoglobulin G, lysozyme, ribonuclease and streptavidin. Direct imaging of template recognition is achieved by patterning a surface at the micrometre scale with imprinted regions.

Platelet adhesion and procoagulant activity induced by contact with radiofrequency glow discharge polymers: roles of adsorbed fibrinogen and vWF.

The potential hemocompatibility of radiofrequency glow discharge (RFGD) polymers made by copolymerization of mixtures of hexafluoropropene and ethylene (C(3)F(6)/C(2)H(4)) or acrylic acid and 1,7-octadiene was investigated using in vitro assays for platelet adhesion and platelet catalyzed thrombin generation. Thrombin generation rate normalized to platelet number was used as a measurement of platelet activation (procoagulant activity). RFGD polymers produced by copolymerization of acrylic acid and 1, 7-octadiene contained varying amounts of carboxylic acid species as determined by electron spectroscopy for chemical analysis (ESCA). These polymers induced little variation in platelet adhesion, thrombin generation, or platelet activation. RFGD polymerization of C(3)F(6) and C(2)H(4) resulted in polymers with varying proportions of fluorinated species, as determined by ESCA. Fibrinogen adsorption from plasma was maximal on a polymer made with 25% C(3)F(6) (75% C(2)H(4)) in the feed. However von Willebrand factor (vWF) adsorption was greater on polymers made with increased %C(3)F(6) in the feed. Platelet adhesion decreased with increasing %C(3)F(6) in the feed. Thrombin generation was lowest for platelets adherent to polymers made from both C(3)F(6) and C(2)H(4). Therefore, procoagulant activity of platelets increased for polymers made with increased %C(3)F(6) in the feed, similar to the trend in vWF adsorption. These findings suggest that increased incorporation of fluorinated species into RFGD polymers leads to decreased platelet adhesion and increased platelet activation (which is possibly due to increased vWF adsorption).