VASP, zyxin and TES are tension-dependent members of Focal Adherens Junctions independent of the α-catenin-vinculin module

Mechanical forces are integrated at cadherin-based adhesion complexes to regulate morphology and strength of cell-cell junctions and organization of associated F-actin. A central mechanosensor at the cadherin complex is α-catenin, whose stretching recruits vinculin to regulate adhesion strength. The identity of the F-actin regulating signals that are also activated by mechanical forces at cadherin-based junctions has remained elusive. Here we identify the actin-regulators VASP, zyxin and TES as members of punctate, tensile cadherin-based junctions called Focal Adherens Junctions (FAJ) and show that they display mechanosensitive recruitment similar to that of vinculin. However, this recruitment is not altered by destroying or over-activating the α-catenin/vinculin module. Structured Illumination Microscopy (SIM) indicates that these tension sensitive proteins concentrate at locations within FAJs that are distinct from the core cadherin complex proteins. Furthermore, localization studies using mutated versions of VASP and zyxin indicate that these two proteins require binding to each other in order to localize to the FAJs. We conclude that there are multiple force sensitive modules present at the FAJ that are activated at distinct locations along the cadherin-F-actin axis and regulate specific aspects of junction dynamics

Hybrid Peptide Dendrimers for Imaging of Chemokine Receptor 4 (CXCR4) Expression

The chemokine receptor 4 (CXCR4), which is over-expressed in many types of cancer, is an emerging target in the field of molecular imaging and therapeutics. The CXCR4 binding of several peptides, including the cyclic Ac-TZ14011, has already been validated. In this study mono-, di- and tetrameric Ac-TZ14011-containing dendrimers were prepared and functionalized with a multimodality hybrid label, consisting of a Cy5.5-like flourophore and a DTPA chelate. Confocal microscopy revealed that all three dendrimers could target CXCR4 in vitro. The unlabeled dimer and tetramer had a slightly lower affinity for CXCR4 than the unlabeled monomer. However, when labeled with the multimodal label the CXCR4 affinity of the dimer and tetramer was significantly higher compared to the labeled monomer. On top of that, biodistribution studies revealed that the additional peptides in the dimer and tetramer reduced nonspecific tissue binding. Thus, multimerization of the cyclic Ac-TZ14011 peptide reduces the negative influence of the multimodal label on the receptor affinity and the biodistribution