Gb3-binding lectins as potential carriers for transcellular drug delivery

<p><b>Objectives</b>: Epithelial cell layers as well as endothelia forming the blood-brain barrier can drastically reduce the efficiency of drug targeting. Our goal was to investigate lectins recognizing the glycosphingolipid globotriaosylceramide (Gb3) for their potential as carriers for transcytotic drug delivery.</p> <p><b>Methods</b>: We utilized an <i>in vitro</i> model based on Madin-Darby canine kidney cells transfected with Gb3 synthase to characterize transcytosis of the Gb3-binding lectins LecA from <i>Pseudomonas aeruginosa</i> and the B-subunit of Shiga toxin (StxB).</p> <p><b>Results</b>: Both lectins were rapidly transcytosed from the apical to the basolateral plasma membrane and <i>vice versa</i>. Whereas StxB proceeded on retrograde and transcytotic routes, LecA avoided retrograde transport. This differential trafficking could be explained by our observation that LecA and StxB segregated into different domains during endocytosis. Furthermore, inhibiting the small GTPase Rab11a, which organizes trafficking through apical recycling endosomes, blocked basolateral to apical transcytosis of both lectins.</p> <p><b>Conclusions</b>: Gb3-binding lectins are promising candidates for transcytotic drug delivery. Our findings highlight that LecA and StxB, which both bind Gb3 but exhibit dissimilar valence and molecular structures of their carbohydrate binding sites and can take divergent intracellular trafficking routes. This opens up the possibility of developing tailor-made glycosphingolipid-binding carrier lectins, which take optimized trafficking pathways.</p

TCR/CD3- and CD59-mediated Ca²⁺ signaling are dependent on Lck and LAT.

<p>Cluster distribution of Ca²⁺ time traces in differently treated cells upon anti-CD3 and anti-CD59 stimulation. Each color represents the percentage of a certain Ca²⁺ time trace cluster in the cell population. (A) Ca²⁺ measurements were performed with WT cells transiently transfected with negative control siRNA (siNeg), Lck-specific siRNA (siLck), WT cells treated with 10 µM PP2 (PP2), and Lck-deficient J.CaM1.6 cells. Clusters representing Ca²⁺ release patterns are framed in black (89.4±10.1%, 76.5±10.4%, 28.3±39.1%, and 23.4±9.9% upon anti-CD3 stimulation, 36.9±13.2%, 12.7±6.1%, 2.6±2.0%, and 1.2±1.2% upon anti-CD59 stimulation for siNeg, siLck, PP2-treated, and J.CaM1.6 cells, respectively). Mean values from at least two independent experiments, each with three technical replicates, are shown (n ≥ 204 per cell type and condition). (B) Cluster analysis of Ca²⁺ time traces in WT cells transiently transfected with negative control siRNA (siNeg), LAT-specific siRNA (siLAT), and LAT-deficient J.CaM2.5 cells. Clusters representing Ca²⁺ release patterns are framed in black (89.4±10.1%, 73.5±5.8%, and 3.0±2.3% upon anti-CD3 stimulation, 36.9±13.2%, 13.0±6.6%, and 1.7±1.6% upon anti-CD59 stimulation for siNeg, siLAT, and J.CaM2.5 cells, respectively). Mean values from at least three independent experiments, each with three technical replicates, are shown (n ≥ 208 per cell type and condition). Multiple comparison tests for the fractions showing Ca²⁺ release patterns in (A) and (B) were assessed by one-way ANOVA, significances are shown where applicable, ** p < 0.01, *** p < 0.001. (C) Knock-down of target proteins was tested by Western blotting. 48 h after transfection cell lysates from siRNA treated cells were probed with anti-Lck, anti-LAT, and anti-β-actin. J.CaM1.6 cells, J.CaM2.5 cells, and WT cells served as controls.</p

CD59-mediated Ca²⁺ signaling requires CD3ζ expression.

<p>(A) Cluster distribution of Ca²⁺ time traces in WT and TCR^high cells is shown upon anti-CD3 and anti-CD59 stimulation. Each color represents the percentage of a certain Ca²⁺ time trace cluster in the cell population. Clusters representing Ca²⁺ release patterns are framed in black (91.4±2.1% and 92.9±3.9% upon anti-CD3 stimulation, 34.4±16.3% and 72.0±16.6% upon anti-CD59 stimulation in WT and TCR^high cells, respectively). Mean values from two independent experiments, each with three technical replicates are shown (n ≥ 167 per cell type and condition). (B) Cluster distribution of Ca²⁺ time traces in WT, TCR^-, and cells expressing CD8-ζ fusion protein is shown upon anti-CD3 and anti-CD59 stimulation. Each color represents the percentage of a certain Ca²⁺ time trace cluster in the cell population. Clusters representing Ca²⁺ release patterns are framed in black (90.1±1.4%, 1.9±0.7% and 7.4±2.3% upon anti-CD3 stimulation, 25.2±6.8%, 1.6±0.4% and 13.4±1.6% upon anti-CD59 stimulation for WT, TCR^-, and CD8-ζ cells, respectively). Mean values from four independent experiments, each with three technical replicates, are shown (n ≥ 343 per cell type and condition). Multiple comparison tests for the fractions showing Ca²⁺ release patterns in (A) and (B) were assessed by one-way ANOVA, significances are shown where applicable, * p < 0.05, ** p < 0.01, *** p < 0.001.</p

Single-cell Ca²⁺ measurements reveal differential heterogeneity upon anti-CD3 and anti-CD59 stimulation.

<p>Jurkat cells (WT) were loaded with Indo-1/AM followed by stimulation with anti-CD3-, anti-CD59-, or anti-CD71-coated surfaces. Individual Ca²⁺ time traces were measured for 200 s after identification of initial cell-surface contact as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085934#pone-0085934-g001" target="_blank">Figure 1S</a>. (A) Box plots of individual Ca²⁺ time traces generated by analysis of the whole cell population upon anti-CD3, anti-CD59, and anti-CD71 stimulation (black line  =  median, grey area  = 50% of Ca²⁺ time traces, dotted lines  =  75% of Ca²⁺ time traces). (B) Individual Ca²⁺ time traces from single-cell measurements were grouped into 11 clusters by affinity propagation clustering as described in Materials and Methods. Each plot shows the respective Ca²⁺ time traces for a cluster, an exemplar trace for each cluster is shown in black. Clusters representing Ca²⁺ release patterns are framed in black. (C) Stimulus-dependent cluster distribution upon anti-CD3, anti-CD59, and anti-CD71 stimulation in WT cells is shown by stacked bar plots. Each color represents the percentage of a certain Ca²⁺ time trace cluster in the cell population. Clusters representing Ca²⁺ release patterns are framed in black (88.5±4.9%, 31.8±12.0%, and 5.5±5.3% for anti-CD3, anti-CD59, and anti-CD71 stimulation, respectively). Mean values from at least three independent experiments, each with three technical replicates, are shown (n ≥ 249 per stimulatory condition). (D) CD3ε and CD59 surface expression levels in WT cells. WT cells were surface stained with Alexa Fluor 647-conjugated anti-CD3ε and FITC-conjugated anti-CD59 or isotype controls and analyzed by flow cytometry. Live cells were gated based on the Forward Scatter and Side Scatter profiles and propidium iodide exclusion. A representative dot plot of four technical replicates is shown.</p

Lck expression and anti-CD59 stimulation influence CD3 surface expression.

<p>WT cells were transfected with negative control siRNA (siNeg) or Lck-specific siRNA (siLck) and experiments were performed 48 h after transfection. (A) Testing of Lck knock-down efficiency. Cell lysates were probed by Western blotting for Lck expression and β-actin as a control. (B) Efficiency of Lck knock-down tested by ensemble Ca²⁺ measurements. siLck and siNeg cells were loaded with Indo-1/AM. Cells were incubated with anti-CD59 mAb or anti-IgG2a for 5 min at 37 °C. For antibody cross-linking, goat anti-mouse F(ab’)₂ was added to samples and Ca²⁺ mobilization of the whole cell population was measured by a microplate reader. For testing TCR surface expression levels, cells were stimulated with anti-CD59 or anti-IgG2a, as isotype control, followed by incubation with goat anti-mouse F(ab’)₂ for (C) 1 h or (D) 15 h at 37°C. Cells were surface stained at 4 °C with FITC-conjugated anti-CD3ε or isotype control and analyzed by flow cytometry. Live cells were gated based on the Forward Scatter and Side Scatter profiles and propidium iodide exclusion. Fluorescence values displayed are isotype control corrected. Representative results of two separate experiments are shown (mean ±SD, n = 4). Multiple comparison tests were assessed by one-way ANOVA, significances are shown where applicable, ***p < 0.001.</p

Reconstitution of Lck by forced interaction of CD3ζ and Lck facilitates TCR/CD3- but not CD59-mediated Ca²⁺ signaling.

<p>(A) Lck expression levels in WT cells, J.CaM1.6 cells and J.CaM1.6 cells expressing mEGFP-tagged Lck fused to CD3ζ (CD3ζ-Lck) were tested by Western blotting, the same blot was reprobed using anti-β-actin as a control. (B) Plasma membrane localization of CD3ζ-Lck-mEGFP in J.CaM1.6 cells was imaged by fluorescence microscopy. CD3ζ-Lck-mEGFP fluorescence and a bright field (BF) image of a transfected J.CaM1.6 cell are shown (scale bars  =  10 µm). (C) Cluster distribution of Ca²⁺ time traces in Lck-deficient J.CaM1.6 cells and J.CaM1.6 cells stably expressing mEGFP-tagged Lck fused to CD3ζ (CD3ζ-Lck) is shown upon anti-CD3 or anti-CD59 stimulation. Each color represents the percentage of a certain Ca²⁺ time trace cluster in the cell population. Clusters representing Ca²⁺ release patterns are framed in black (35.7±4.9% and 71.8±2.3% upon anti-CD3 stimulation, 1.4±2.3% and 1.0±1.3% upon anti-CD59 stimulation for J.CaM1.6 and CD3ζ-Lck cells, respectively). Mean values from three independent experiments, each with three technical replicates, are shown (n ≥ 323 per cell type and condition). Multiple comparison tests for the fractions showing Ca²⁺ release patterns were assessed by one-way ANOVA, significances are shown where applicable, ***p < 0.001.</p

Adsorption and Inactivation of SARS-CoV‑2 on the Surface of Anatase TiO₂(101)

We investigated the adsorption of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), the virus responsible for the current pandemic, on the surface of the model catalyst TiO2(101) using atomic force microscopy, transmission electron microscopy, fluorescence microscopy, and X-ray photoelectron spectroscopy, accompanied by density functional theory calculations. Three different methods were employed to inactivate the virus after it was loaded on the surface of TiO2(101): (i) ethanol, (ii) thermal, and (iii) UV treatments. Microscopic studies demonstrate that the denatured spike proteins and other proteins in the virus structure readsorb on the surface of TiO2 under thermal and UV treatments. The interaction of the virus with the surface of TiO2 was different for the thermally and UV treated samples compared to the sample inactivated via ethanol treatment. AFM and TEM results on the UV-treated sample suggested that the adsorbed viral particles undergo damage and photocatalytic oxidation at the surface of TiO2(101) which can affect the structural proteins of SARS-CoV-2 and denature the spike proteins in 30 min. The role of Pd nanoparticles (NPs) was investigated in the interaction between SARS-CoV-2 and TiO2(101). The presence of Pd NPs enhanced the adsorption of the virus due to the possible interaction of the spike protein with the NPs. This study is the first investigation of the interaction of SARS-CoV-2 with the surface of single crystalline TiO2(101) as a potential candidate for virus deactivation applications. Clarification of the interaction of the virus with the surface of semiconductor oxides will aid in obtaining a deeper understanding of the chemical processes involved in photoinactivation of microorganisms, which is important for the design of effective photocatalysts for air purification and self-cleaning materials