Adiponectin is an adipose derived hormone that declines in obesity. We have previously shown that exogenous administration of adiponectin reduces allergic airways responses in mice. T-cadherin (T-cad; Cdh13) is a binding protein for the high molecular weight isoforms of adiponectin. To determine whether the beneficial effects of adiponectin on allergic airways responses require T-cad, we sensitized wildtype (WT), T-cadherin deficient (T-cad(-/-)) and adiponectin and T-cad bideficient mice to ovalbumin (OVA) and challenged the mice with aerosolized OVA or PBS. Compared to WT, T-cad(-/-) mice were protected against OVA-induced airway hyperresponsiveness, increases in BAL inflammatory cells, and induction of IL-13, IL-17, and eotaxin expression. Histological analysis of the lungs of OVA-challenged T-cad(-/-) versus WT mice indicated reduced inflammation around the airways, and reduced mucous cell hyperplasia. Combined adiponectin and T-cad deficiency reversed the effects of T-cad deficiency alone, indicating that the observed effects of T-cad deficiency require adiponectin. Compared to WT, serum adiponectin was markedly increased in T-cad(-/-) mice, likely because adiponectin that is normally sequestered by endothelial T-cad remains free in the circulation. In conclusion, T-cad does not mediate the protective effects of adiponectin. Instead, mice lacking T-cad have reduced allergic airways disease, likely because elevated serum adiponectin levels act on other adiponectin signaling pathways.
Sound detection by inner ear hair cells requires tip links that interconnect mechanosensory stereocilia and convey force to yet unidentified transduction channels. Current models postulate a static composition of the tip link, with protocadherin 15 (PCDH15) at the lower and cadherin 23 (CDH23) at the upper end of the link. In terminally differentiated mammalian auditory hair cells, tip links are subjected to sound-induced forces throughout an organism’s life. Although hair cells can regenerate disrupted tip links and restore hearing, the molecular details of this process are unknown. We developed a novel implementation of backscatter electron scanning microscopy to visualize simultaneously immuno-gold particles and stereocilia links, both of only a few nanometers in diameter. We show that functional, mechanotransduction-mediating tip links have at least two molecular compositions, containing either PCDH15/CDH23 or PCDH15/PCDH15. During regeneration, shorter tip links containing nearly equal amounts of PCDH15 at both ends appear first. Whole-cell patch-clamp recordings demonstrate that these transient PCDH15/PCDH15 links mediate mechanotransduction currents of normal amplitude but abnormal Ca(2+)-dependent decay (adaptation). The mature PCDH15/CDH23 tip link composition is re-established later, concomitant with complete recovery of adaptation. Thus, our findings provide a molecular mechanism for regeneration and maintenance of mechanosensory function in postmitotic auditory hair cells and could help identify elusive components of the mechanotransduction machinery.
Contact inhibition of locomotion (CIL) is the process through which cells move away from each other after cell-cell contact, and it contributes to malignant invasion and developmental migration. Various cell types exhibit CIL, whereas others remain in contact after collision and may form stable junctions. To investigate what determines this differential behavior, we study neural crest cells, a migratory stem cell population whose invasiveness has been likened to cancer metastasis. By comparing pre-migratory and migratory neural crest cells, we show that the switch from E- to N-cadherin during EMT is essential for acquisition of CIL behavior. Loss of E-cadherin leads to repolarization of protrusions, via p120 and Rac1, resulting in a redistribution of forces from intercellular tension to cell-matrix adhesions, which break down the cadherin junction. These data provide insight into the balance of physical forces that contributes to CIL in cells in vivo.
Tissues and organs undergo constant physical perturbations and individual cells must respond to mechanical forces to maintain tissue integrity. However, molecular interactions underlying mechano-transduction are not fully defined at cell-cell junctions. This is in part due to weak and transient interactions that are likely prevalent in force-induced protein complexes. Using in situ proximal biotinylation by the promiscuous biotin ligase BirA tagged to α-catenin and a substrate stretch cell chamber, we sought to identify force-dependent molecular interactions surrounding α-catenin, an actin regulator at the sites of cadherin mediated cell-cell adhesion. While E-cadherin, β-catenin, vinculin and actin localize with α-catenin at cell-cell contacts in immuno-fluorescent staining, only β-catenin and plakoglobin were biotinylated, suggesting that this proximal biotinylation is limited to the molecules that are in the immediate vicinity of α-catenin. In mechanically stretched samples, increased biotinylation of non-muscle myosin IIA, but not myosin IIB, suggests close spatial proximity between α-catenin and myosin IIA during substrate stretching. This force-induced biotinylation diminished as myosin II activity was inhibited by blebbistatin. Taken together, this promising technique enables us to identify force sensitive complexes that may be essential for mechano-responses in force bearing cell adhesion.
Classical cadherins are well known for their essential function in mediating cell-cell adhesion via their extra-cellular cadherin domains and intra-cellular connections to the actin cytoskeleton [1-3]. There is evidence, however, of adhesion-independent cadherin clusters existing outside of cell-cell junctions [4-6]. What function, if any, these clusters have is not known. HMR-1, the sole classical cadherin in Caenorhabditis elegans, plays essential roles during gastrulation, blastomere polarity establishment, and epidermal morphogenesis [7-11]. To elucidate the physiological roles of non-junctional cadherin, we analyzed HMR-1 in the C. elegans zygote, which is devoid of neighbors. We show that non-junctional clusters of HMR-1 form during the one-cell polarization stage and associate with F-actin at the cortex during episodes of cortical flow. Non-junctional HMR-1 clusters downregulate RHO-1 activity and inhibit accumulation of non-muscle myosin II (NMY-2) at the anterior cortex. We found that HMR-1 clusters impede cortical flows and play a role in preserving the integrity of the actomyosin cortex, preventing it from splitting in two. Importantly, we uncovered an inverse relationship between the amount of HMR-1 at the cell surface and the rate of cytokinesis. The effect of HMR-1 clusters on cytokinesis is independent of their effect on NMY-2 levels, and is also independent of their extra-cellular domains. Thus, in addition to their canonical role in inter-cellular adhesion, HMR-1 clusters regulate RHO-1 activity and NMY-2 level at the cell surface, reinforce the stability of the actomyosin cortex, and resist its movement to influence cell-shape dynamics.
In the olfactory epithelium (OE), olfactory cells (OCs) and supporting cells (SCs), which express different cadherins, are arranged in a characteristic mosaic pattern in which OCs are enclosed by SCs. However, the mechanism underlying this cellular patterning is unclear. Here, we show that the cellular pattern of the OE is established by cellular rearrangements during development. In the OE, OCs express nectin-2 and N-cadherin, and SCs express nectin-2, nectin-3, E-cadherin, and N-cadherin. Heterophilic trans-interaction between nectin-2 on OCs and nectin-3 on SCs preferentially recruits cadherin via α-catenin to heterotypic junctions, and the differential distributions of cadherins between junctions promote cellular intercalations, resulting in the formation of the mosaic pattern. These observations are confirmed by model cell systems, and various cellular patterns are generated by the combinatorial expression of nectins and cadherins. Collectively, the synergistic action of nectins and cadherins generates mosaic pattern, which cannot be achieved by a single mechanism.
Dynamics of epithelial tissues determine key processes in development, tissue healing and cancer invasion. These processes are critically influenced by cell-cell adhesion forces. However, the identity of the proteins that resist and transmit forces at cell-cell junctions remains unclear, and how these proteins control tissue dynamics is largely unknown. Here we provide a systematic study of the interplay between cell-cell adhesion proteins, intercellular forces and epithelial tissue dynamics. We show that collective cellular responses to selective perturbations of the intercellular adhesome conform to three mechanical phenotypes. These phenotypes are controlled by different molecular modules and characterized by distinct relationships between cellular kinematics and intercellular forces. We show that these forces and their rates can be predicted by the concentrations of cadherins and catenins. Unexpectedly, we identified different mechanical roles for P-cadherin and E-cadherin; whereas P-cadherin predicts levels of intercellular force, E-cadherin predicts the rate at which intercellular force builds up.
The intracellular functions of classical cadherins are mediated through the direct binding of two catenins: β-catenin and p120catenin. While β-catenin is crucial for cadherin function, the role of p120catenin is less clear and appears to vary between organisms. We show here that p120catenin has a conserved role in regulating the endocytosis of cadherins, but that its ancestral role may have been to promote endocytosis, followed by the acquisition of a novel inhibitory role in vertebrates. In Drosophila, p120catenin facilitates endocytosis of the dynamic E-cadherin-Bazooka subcomplex, which is followed by its recycling. The absence of p120catenin stabilizes this subcomplex at the membrane, reducing the ability of cells to exchange neighbours in embryos and expanding cell-cell contacts in imaginal discs.
Hearing and balance use hair cells in the inner ear to transform mechanical stimuli into electrical signals. Mechanical force from sound waves or head movements is conveyed to hair-cell transduction channels by tip links, fine filaments formed by two atypical cadherins known as protocadherin 15 and cadherin 23 (refs 4, 5). These two proteins are involved in inherited deafness and feature long extracellular domains that interact tip-to-tip in a Ca(2+)-dependent manner. However, the molecular architecture of this complex is unknown. Here we combine crystallography, molecular dynamics simulations and binding experiments to characterize the protocadherin 15-cadherin 23 bond. We find a unique cadherin interaction mechanism, in which the two most amino-terminal cadherin repeats (extracellular cadherin repeats 1 and 2) of each protein interact to form an overlapped, antiparallel heterodimer. Simulations predict that this tip-link bond is mechanically strong enough to resist forces in hair cells. In addition, the complex is shown to become unstable in response to Ca(2+) removal owing to increased flexure of Ca(2+)-free cadherin repeats. Finally, we use structures and biochemical measurements to study the molecular mechanisms by which deafness mutations disrupt tip-link function. Overall, our results shed light on the molecular mechanics of hair-cell sensory transduction and on new interaction mechanisms for cadherins, a large protein family implicated in tissue and organ morphogenesis, neural connectivity and cancer.
Gastric adenocarcinoma originates from an abnormal epithelium. The aim of this study was to investigate the expression of sodium-potassium ATPase (NKA), a transmembrane protein located in the epithelium for Na+ and K+ transportation, and E-cadherin, which are both crucial for the epithelium and adherens junction, as potential gastric cancer biomarkers.