Nedd4 family-interacting protein 1 (Ndfip1) is required for the exosomal secretion of Nedd4 family proteins

The ability to remove unwanted proteins is an important cellular feature. Classically, this involves the enzymatic addition of ubiquitin moieties followed by degradation in the proteasome. Nedd4 proteins are ubiquitin ligases important not only for protein degradation, but also for protein trafficking. Nedd4 proteins can bind to target proteins either by themselves or through adaptor protein Ndfip1 (Nedd4 family-interacting protein 1). An alternative mechanism for protein removal and trafficking is provided by exosomes, which are small vesicles (50-90-nm diameter) originating from late endosomes and multivesicular bodies (MVBs). Exosomes provide a rapid means of shedding obsolete proteins and also for cell to cell communication. In the present work, we show that Ndfip1 is detectable in exosomes secreted from transfected cells and also from primary neurons. Compared with control, Ndfip1 increases exosome secretion from transfected cells. Furthermore, while Nedd4, Nedd4-2, and Itch are normally absent from exosomes, expression of Ndfip1 results in recruitment of all three Nedd4 proteins into exosomes. Together, these results suggest that Ndfip1 is important for protein trafficking via exosomes, and provides a mechanism for cargoing passenger proteins such as Nedd4 family proteins. Given the positive roles of Ndfip1/Nedd4 in improving neuronal survival during brain injury, it is possible that exosome secretion provides a novel route for rapid sequestration and removal of proteins during stress.     

Laminins promote postsynaptic maturation by an autocrine mechanism at the neuromuscular junction

A prominent feature of synaptic maturation at the neuromuscular junction (NMJ) is the topological transformation of the acetylcholine receptor (AChR)-rich postsynaptic membrane from an ovoid plaque into a complex array of branches. We show here that laminins play an autocrine role in promoting this transformation. Laminins containing the α4, α5, and β2 subunits are synthesized by muscle fibers and concentrated in the small portion of the basal lamina that passes through the synaptic cleft at the NMJ. Topological maturation of AChR clusters was delayed in targeted mutant mice lacking laminin α5 and arrested in mutants lacking both α4 and α5. Analysis of chimeric laminins in vivo and of mutant myotubes cultured aneurally demonstrated that the laminins act directly on muscle cells to promote postsynaptic maturation. Immunohistochemical studies in vivo and in vitro along with analysis of targeted mutants provide evidence that laminin-dependent aggregation of dystroglycan in the postsynaptic membrane is a key step in synaptic maturation. Another synaptically concentrated laminin receptor, Bcam, is dispensable. Together with previous studies implicating laminins as organizers of presynaptic differentiation, these results show that laminins coordinate post- with presynaptic maturation.     

A scapular coordinate frame for clinical and kinematic analyses

The aim of this study was to define a body-fixed coordinate frame for the scapula that minimises axes variability and is closely related to the clinical frame of reference. Medical images of 21 scapulae were used to quantify 14 different axes from identifiable landmarks. The plane of the blade of the scapula was defined. The orientations of the quantified axes were calculated. The angular relationships between axes were quantified and applied to grade the sensitivity of each axis to inter-scapular variations in the others. The volume of data required to define an axis was noted for its dependency on pathology and the three criteria were weighted according to relative importance. The two axes with the highest weighting were applied to define a body-fixed Cartesian coordinate frame for the scapula. A least square medio-lateral line through the centre of the spine root was the most optimal axis. The plane formed by the spine root line and a least square line through the centre of the lateral border ridge was the most optimal scapular plane. This body-fixed Cartesian coordinate frame is closely aligned to the cardinal planes in the anatomical position and thus is a clinically applicable, specimen invariant coordinate frame that can be used in patient-specific kinematics modelling.     

Acquisition of full-field strain distributions on ovine fracture callus cross-sections with electronic speckle pattern interferometry

This study evaluated the feasibility of assessing continuous strain distributions on fracture callus cross-sections with an electronic speckle pattern interferometry (ESPI) system. Mid-sagittal callus cross-sections were harvested from ovine tibiae. One low stiffness (LS) specimen and one high stiffness (HS) specimen were selected to evaluate the feasibility for strain acquisition over a range of callus properties. The HS specimen was 147 times stiffer in compression than the LS specimen. ESPI captured continuous strain distributions on both specimens. Peak strain was located adjacent to cortical boundaries in the osteotomy gap. In response to 5N compression, peak compressive strain of 5.8% in the LS specimen was over two orders of magnitude higher than peak compressive strain of 0.013% in the HS specimen. In conclusion, ESPI-based strain acquisition enables reproducible quantification of strain distributions on callus cross-sections. Such measurements may support validation of computational models and evaluation of experimental results in fracture healing research.     

RACK1 and CIS mediate the degradation of BimEL in cancer cells

RACK1 is a 7-WD motif-containing protein with numerous downstream effectors regulating various cellular functions. Using a yeast two-hybrid screen, we identified dynein light chain 1 as a novel interacting partner of RACK1. Additionally, we demonstrated that RACK1 formed a complex with DLC1 and Bim, specifically BimEL, in the presence of apoptotic agents. Upon paclitaxel treatment, RACK1, DLC1, and CIS mediated the degradation of BimEL through the ElonginB/C-Cullin2-CIS ubiquitin-protein isopeptide ligase complex. We further showed that RACK1 conferred paclitaxel resistance to breast cancer cells in vitro and in vivo. Finally, we observed an inverse correlation between CIS and BimEL levels in both ovarian and breast cancer cell lines and specimens. Our study suggests a role of RACK1 in protecting cancer cells from apoptosis by regulating the degradation of BimEL, which together with CIS could play an important role of drug resistance in chemotherapy.     

Optical tweezers to study <Emphasis Type="Italic">single</Emphasis> Protein A/Immunoglobulin G interactions at varying conditions

Optical tweezers (OT) are ideally suited to study the interaction of single receptor-ligand bonds. Here we introduce a newly developed assay using OT to investigate the interactions between Protein A from Staphylococcus aureus and Immunoglobulin G from rabbit serum (RIgG). We demonstrate that the rupture forces depend on the loading rate and on the sodium chloride concentration. The measured loading rate effect is well known in the literature and the data we obtained were found to be in good agreement with an already published theoretical model. The dependence of the rupture forces on the salt concentration demonstrates the influence of hydrophobic interactions on the bond strength. Our experimental setup can probe the interaction between a single receptor and its specific ligand under changing conditions and hence offers manifold applications in single molecule biotechnology.     

Time resolved secretion of chloride from a monolayer of mucin-secreting epithelial cells

Short-circuit current (Isc) measurement is used to quantify transepithelial ion flux. This technique provides a direct measure of net charge transport across a cell monolayer. Isc however, lacks chemical selectivity. Chemically resolved ion fluxes may be much greater than Isc, and differ in different biological processes. This work describes a novel experimental approach and deconvolution method to obtain temporally resolved ion fluxes at epithelial cell monolayers. HT29-Cl.16E cells, a sub clone of the human colonic cancer cell line HT29 was used as a model cell line to validate this approach in the context of epithelial transport studies. This cell line is known to secrete chloride in response to purinergic stimulation. Changes in chloride concentration after stimulation with 1 mM ATP plus 50 nM phorbol-myristate acetate (PMA) are recorded with a chloride ion-selective electrode (ISE) at a short distance (∼50 μm) from the monolayer. The recorded concentrations are transformed to corresponding chloride flux across the monolayer using a deconvolution algorithm for extracellular mass transport based on minimization of the shape error function (Nair and Gratzl in Anal Chem 77:2875–2888, 2005). Simultaneous voltage clamp yields the associated net electrical charge flux (Isc). The dynamics of Cl⁻ flux did correlate with that of the electrical flux, but was found to be greater in amplitude. This suggests that Cl⁻ may not be the only ion secreted. The method of simultaneously assessing ionic and electrical fluxes with a temporal resolution of seconds provides unique information about the dynamics of solute fluxes across the apical membrane. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Transport at the nanoscale: temperature dependence of ion conductance

Temperature dependent ion conductance in nanopores is measured in a wide range of electrolyte concentrations and compared with molecular modeling. Single outer membrane protein F (OmpF) channels from E. coli are reconstituted into planar lipid bilayers. In qualitative agreement with the experimental data, applied-field molecular dynamics unraveled atomistic details of the ion transport. Comparing the temperature dependence of the channel conductance with that of the bulk conductivity in the range from 0 to 90°C revealed that at low salt concentrations the transport is mainly driven along the pore surface. Increasing the salt concentration saturates the surface charge transport and induces ion transport in the center of the nanopore. The confinement of the nanopore then favors the formation of ion pairs. Stepping up the temperature reduces the life time of the ion pairs and increases the channel conductance more than expected from the bulk behavior.     

The effect of strain rate on the mechanical properties of human cortical bone

Bone mechanical properties are typically evaluated at relatively low strain rates. However, the strain rate related to traumatic failure is likely to be orders of magnitude higher and this higher strain rate is likely to affect the mechanical properties. Previous work reporting on the effect of strain rate on the mechanical properties of bone predominantly used nonhuman bone. In the work reported here, the effect of strain rate on the tensile and compressive properties of human bone was investigated. Human femoral cortical bone was tested longitudinally at strain rates ranging between 0.14-29.1 s(-1) in compression and 0.08-17 s(-1) in tension. Young's modulus generally increased, across this strain rate range, for both tension and compression. Strength and strain (at maximum load) increased slightly in compression and decreased (for strain rates beyond 1 s(-1)) in tension. Stress and strain at yield decreased (for strain rates beyond 1 s(-1)) for both tension and compression. In general, there seemed to be a relatively simple linear relationship between yield properties and strain rate, but the relationships between postyield properties and strain rate were more complicated and indicated that strain rate has a stronger effect on postyield deformation than on initiation of yielding. The behavior seen in compression is broadly in agreement with past literature, while the behavior observed in tension may be explained by a ductile to brittle transition of bone at moderate to high strain rates.