Structure of native oligomeric Sprouty2 by electron microscopy and its property of electroconductivity

Identification of key features required for efficient S-acylation and plasma membrane targeting of sprouty-2

Sprouty-2 is an important regulator of growth factor signalling and a tumour suppressor protein. The defining feature of this protein is a cysteine-rich domain (CRD) that contains twenty-six cysteine residues and is modified by S-acylation. In this study, we show that the CRD of sprouty-2 is differentially modified by S-acyltransferase enzymes. The high specificity/low activity zDHHC17 enzyme mediated restricted S-acylation of sprouty-2, and cysteine-265 and -268 were identified as key targets of this enzyme. In contrast, the low specificity/high activity zDHHC3 and zDHHC7 enzymes mediated more expansive modification of the sprouty-2 CRD. Nevertheless, S-acylation by all enzymes enhanced sprouty-2 expression, suggesting that S-acylation stabilises this protein. In addition, we identified two charged residues (aspartate-214 and lysine-223), present on opposite faces of a predicted α-helix in the CRD, which are essential for S-acylation of sprouty-2. Interestingly, mutations that perturbed S-acylation also led to a loss of plasma membrane localisation of sprouty-2 in PC12 cells. This study provides insight into the mechanisms and outcomes of sprouty-2 S-acylation, and highlights distinct patterns of S-acylation mediated by different classes of zDHHC enzymes.

Subcellular Localization of Sprouty2 in Human Glioma Cells

Sprouty proteins act ubiquitously as signaling integrators and inhibitors of receptor tyrosine kinase (RTK) activated pathways. Among the four Sprouty isoforms, Sprouty2 is a key regulator of growth factor signaling in several neurological disorders. High protein levels correlate with reduced survival of glioma patients. We recently demonstrated that abrogating its function inhibits tumor growth by overstimulation of ERK and induction of DNA replication stress. The important role of Sprouty2 in the proliferation of malignant glioma cells prompted us to investigate its subcellular localization applying super-resolution fluorescence and immunoelectron microscopy. We found that cytoplasmic Sprouty2 is not homogenously distributed but localized to small spots (<100 nm) partly attached to vimentin filaments and co-localized with activated ERK. The protein is associated with early, late and recycling endosomes in response to but also independently of growth factor stimulation. The subcellular localization of Sprouty2 in all areas exhibiting strong RTK activities may reflect a protective response of glioma cells to limit excessive ERK activation and to prevent cellular senescence and apoptosis.

Laminin γ2-enriched extracellular vesicles of oral squamous cell carcinoma cells enhance in vitro lymphangiogenesis via integrin α3-dependent uptake by lymphatic endothelial cells

Oral squamous cell carcinoma (OSCC) LN1-1 cells previously showed greater capacities for lymphangiogenesis and lymph node metastasis compared to their parental OEC-M1 cells, in addition to an ability to enhance the migration and tube formation of lymphatic endothelial cells (LECs). Purified by a series of differential centrifugations and characterized using electron microscopy, dynamic light scattering and western blot, LN1-1 cell-derived extracellular vesicles (LN1-1 EVs) were shown to promote LEC migration, tube formation and uptake by LECs more effectively than did OEC-M1 cell-derived EVs (OEC-M1 EVs). Using stable isotope labeling with amino acids in cell culture/liquid chromatography-tandem mass spectrometry-based proteomic platform, the laminin-332 proteins, including laminin α3, β3 and γ2, were validated as highly expressed proteins in LN1-1 EVs. Clinically, a higher level of laminin-332 was detected in plasma EVs from OSCC patients with lymph node metastasis than in both healthy controls and OSCC patients without lymphatic metastasis, suggesting EV-borne laminin-332 as a novel and noninvasive biomarker for the detection of lymph node metastasis in OSCC. The knockdown of laminin γ2 and inhibition by anti-laminin-332 neutralizing antibodies impaired LN1-1 EV-mediated LEC migration, tube formation and uptake by LECs. Importantly, laminin γ2-deficient EVs showed a reduced ability to drain into lymph nodes in comparison with the control EVs. In addition, the laminin 332/γ2-mediated EV uptake was dependent on integrin α3 but not β1, β4 or α6. Collectively, the uptake of laminin γ2-enriched EVs by LECs enhanced in vitro lymphangiogenesis and EV-borne laminin-332 is thus a viable biomarker for OSCC.

Modulations of SIR-nucleosome interactions of reconstructed yeast silent pre-heterochromatin by O-acetyl-ADP-ribose and magnesium

In vitro–assembled filaments are confirmed as SIR-nucleosome pre-heterochromatin, and AAR acts as a modulator for their formation. Not only is magnesium present in the environmental buffer, but it also is chelated by the SIR-nucleosome pre-heterochromatin to promote its condensation.

Yeast silent heterochromatin provides an excellent model with which to study epigenetic inheritance. Previously we developed an in vitro assembly system to demonstrate the formation of filament structures with requirements that mirror yeast epigenetic gene silencing in vivo. However, the properties of these filaments were not investigated in detail. Here we show that the assembly system requires Sir2, Sir3, Sir4, nucleosomes, and O-acetyl-ADP-ribose. We also demonstrate that all Sir proteins and nucleosomes are components of these filaments to prove that they are SIR-nucleosome filaments. Furthermore, we show that the individual localization patterns of Sir proteins on the SIR-nucleosome filament reflect those patterns on telomeres in vivo. In addition, we reveal that magnesium exists in the SIR-nucleosome filament, with a role similar to that for chromatin condensation. These results suggest that a small number of proteins and molecules are sufficient to mediate the formation of a minimal yeast silent pre-heterochromatin in vitro.

Specific detection of CD133-positive tumor cells with iron oxide nanoparticles labeling using noninvasive molecular magnetic resonance imaging

Background

The use of ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles to visualize cells has been applied clinically, showing the potential for monitoring cells in vivo with magnetic resonance imaging (MRI). USPIO conjugated with anti-CD133 antibodies (USPIO-CD133 Ab) that recognize the CD133 molecule, a cancer stem cell marker in a variety of cancers, was studied as a novel and potent agent for MRI contrast enhancement of tumor cells.

Materials and methods

Anti-CD133 antibodies were used to conjugate with USPIO via interaction of streptavidin and biotin for in vivo labeling of CD133-positive cells in xenografted tumors and N-ethyl-N-nitrosourea (ENU)-induced brain tumors. The specific binding of USPIO-CD133 Ab to CD133-positive tumor cells was subsequently detected by Prussian blue staining and MRI with T2-weighted, gradient echo and multiple echo recombined gradient echo images. In addition, the cellular toxicity of USPIO-CD133 Ab was determined by analyzing cell proliferation, apoptosis, and reactive oxygen species production.

Results

USPIO-CD133 Ab specifically recognizes in vitro and labels CD133-positive cells, as validated using Prussian blue staining and MRI. The assays of cell proliferation, apoptosis, and reactive oxygen species production showed no significant differences in tumor cells with or without labeling of USPIO-CD133 Ab. In vivo imaging of CD133-positive cells was demonstrated by intravenous injection of USPIO-CD133 Ab in mice with HT29 xenografted tumors. The MRI of HT29 xenografts showed several clusters of hypotensive regions that correlated with CD133 expression and Prussian blue staining for iron. In rat, brain tumors induced by transplacental ENU mutagenesis, several clusters of hypointensive zones were observed in CD133-expressing brain tumors by MRI and intravenously administered USPIO-CD133 Ab.

Conclusion

Combination of USPIO-CD133 Ab and MRI is valuable in recognizing CD133-expressing tumor cells in vitro, extracellularly labeling for cell tracking and detecting CD133-expressing tumors in xenografted tumors as well as ENU-induced rat brain tumors.